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2000 - July 20/22 University of Cambridge Talk Abstracts
Article Index
2000 - July 20/22 University of Cambridge Talk Abstracts
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Wednesday July 19, 6pm

The Hebb Award Lecture

Making sense of humours

Jane Stewart

Concordia University

In the study of motivation and emotion, body 'humours' have long played an explanatory role. This talk will be concerned with how our concepts of 'humours' have evolved. Using examples from recent behavioral studies I will discuss how modern knowledge of the effects of the ever increasing numbers of 'humours' and their modes of influence is increasing our understanding of how motivational states are induced, about the role of learning in motivation and about how state variables alter behavior.

Session A - Thursday 20 July 9-10.40 am

Symposium: "Role of knowledge, logic & normative standards in human inference"

Organiser: Valerie Thompson

The role of suppositions in the development of children's reasoning

Simon Handley and Joanna Lott

University of Plymouth

This paper reports the results of two experiments that examined the development of conditional reasoning in six age groups (7,9,11,13,15,17 and adult). Rule-based theories of deduction provide detailed accounts of the developmental stages in conditional reasoning. These theories predict a reduction in Modus Tollens (MT) reasoning in mid to late adolescence as children begin to resist invited inferences but do not possess competence in applying the indirect suppositional strategies necessary to solve MT. However, the evidence for this trend in MT reasoning is equivocal and depends to a great extent on the method of problem presentation. In Experiment 1 we presented conditional syllogisms to six age groups, carefully controlling the presentation of the problems. The results showed a general increase in reasoning competence with age, a reduction in fallacies amongst the older age groups and a significant reduction in MT reasoning at 17 years of age. In Experiment 2 we used the negations paradigm, with conclusions to be evaluated that were either consistent or inconsistent with the logical conclusion. Two notable effects emerged an increase in negative conclusion bias with age and higher rates of MT reasoning amongst the older age groups on those problems in which the inconsistent conclusion was presented. We interpret these findings as resulting from the development of the same underlying competence; the ability to engage in suppositional reasoning. The implications of the findings are discussed in the context of rule-based and model-based theories of human reasoning.

Probabilities and polarity biases in conditional inference

Mike Oaksford1, Nick Chater2 and Joanne Larkin2

1. Cardiff University

2. University of Warwick

A probabilistic computational level model of conditional inference is proposed that can explain polarity biases in conditional inference (e.g., J. St.B. T. Evans, 1993). These biases are observed when J. St.B. T. Evans' (1972) negations paradigm is used in the conditional inference task. The model assumes that negations define higher probability categories than their affirmative counterparts (M. Oaksford & K. Stenning, 1992), e.g., P(not-dog) > P(dog). This identification suggests that polarity biases are really a rational effect of high probability categories. Three experiments revealed that, consistent with this probabilistic account, when high probability categories are used instead of negations a high probability conclusion effect is observed. In the General Discussion the relationships between the probabilistic model and (i) other phenomena and (ii) other theories, in conditional reasoning are discussed.

Paradoxical individual differences in conditional inference

Jo Sellen and Mike Oaksford

Cardiff University

Paradoxical individual differences, where a dysfunctional trait correlates positively with some preconceived notion of the normatively correct answer, provide compelling evidence that the wrong norm has been adopted. We report a result showing that logical performance on conditional inference is positively correlated with schizotypy. Schizotypy is strongly negatively correlated with IQ. Therefore following Stanovich and West's (in press) reasoning, logic may not be normative in conditional inference, the prototypically logical task. This is consistent with recent models of conditional that take a probabilistic rather than a logical approach (Oaksford, Chater & Larkin, 2000).

Knowledge-based reasoning about causes and consequences

Jonathan Fugelsang and Valerie Thompson

University of Saskatchewan

When evaluating causal candidates, peoples' judgments may be influenced by both the observed empirical evidence (e.g., Cheng, 1997), and the belief in a causal mechanism (e.g., White, 1989). Fugelsang and Thompson (2000) presented a series of experiments which demonstrated that people weigh empirical evidence in light of their pre-existing beliefs, such that empirical evidence is given more weight for believable than for unbelievable candidates. The goal of the current experiments was to determine what elements of a reasoner's beliefs produces this interaction. The results of two experiments demonstrated that it is the belief in a causal mechanism, rather than the belief that the cause and effect covary, that determines the use of empirical evidence.

Background beliefs about the probability of the evidence in hypothesis testing

Aidan Feeney1 and Jonathan Evans2

1. University of Durham

2. University of Plymouth

Previous work (Feeney, Evans and Clibbens, 1997; in press) has demonstrated that people's background beliefs about the probability of the evidence affect both their selection and interpretation of evidence on the pseudodiagnosticity task. I will present the results of two experiments designed to investigate the processes underlying such probabilistic effects. Although both experiments replicate the background belief effect in evidence selection, they also demonstrate that hypothesis testers are inflexible in the face of explicit statistical and implicit contextual manipulations of the likely information to be gained from selecting evidence with low a priori probability. It will be argued that these results suggest the operation of a rarity heuristic in hypothesis testing whilst possible adaptive functions for such a heuristic will also be discussed.

Session B - Thursday 20 July 9-10.40 am

Symposium: "It’s about time"

Organiser: Simon Grondin

The time of my life

Lorraine Allan

McMaster University

Allan and Kristofferson (1974) concluded that "There are few quantitative theories of duration discrimination and few established empirical phenomena to guide theorizing." (p. 26). Five years later, Allan (1979), referring back to Allan and Kristofferson (1974), stated that "Since that time, there has been a dramatic change. Many articles on the discrimination of brief temporal intervals, and several new quantitative models, have appeared in a period of a few years." (p. 340). At BBCS/EPS 2000, it will be two decades since Allan (1979). We now have an abundance of sophisticated quantitative models for time perception and a wealth of intriguing empirical data. My contribution to the ITS ABOUT TIME symposium will be a personally-oriented tour through the psychophysical timing literature of the past two decades.

Temporal discrimination and temporal differentiation of behaviour: Evidence for distinct neural mechanisms

C M Bradshaw, M-Y Ho, T-J Chiang, S Mobini and E Szabadi

Psychopharmacology Section, Division of Psychiatry, University of Nottingham

Schedules used to assess timing in animals include 'retrospective timing schedules', in which animals are trained to emit different responses following stimuli of different durations (temporal discrimination), and 'immediate timing schedules', in which behaviour is regulated during an ongoing interval (temporal differentiation). Observations that the phenomena of timing behaviour are similar in these two types of schedule have encouraged the belief that (a) a common timing mechanism underlies temporal discrimination and temporal differentiation, and (b) quantitative indices of timing derived from either type of schedule may be used interchangeably to investigate the properties of this mechanism. However, these assumptions are challenged by evidence that neurobiological interventions can selectively alter timing indices in some schedules but not others. This paper discusses evidence from experiments in which central monoaminergic functions were manipulated by acute drug treatment and lesions; it is proposed that the findings are inconsistent with the concept of a unitary pacemaker-driven internal clock.

It's about time making sense, or perhaps about senses making time

Simon Grondin

Université Laval, Québec

Time judgments are often reported to be based on the output of a central clock. Such a view assumes that for whatever sensory-modality condition under investigation, sensory signals are temporally linked by the product of this central source of time. In this case, time in itself contributes to the making of the sensory organization. On the other hand, psychological time can be approached as an emergent property of the organization between sensory events within any given sensory modality. That is to say, the senses are what make time. Studies stemming from the clock perspective and involving sensory modality comparisons for duration discrimination are briefly reviewed. As well, the implications of adopting a "sense-making-time" approach are presented for one case, that of visual modality.


Peter R Killeen

Arizona State University, USA

Forgetting curves in delayed matching-to-sample (DMTS) experiments are too steep to be credible evidence for rapid forgetting of stimuli that are so very-well known. Instead, animals are deciding whether the remembered stimulus occurred on this trial or on the previous one. This is judgement of recency (JOR). Several models of temporal confusion are reviewed; the simplest, scalar timing, makes parameter-free predictions that approximate DMTS data over various manipulations.

Infernal machines! Exploring internal clocks and other timing processes

J H Wearden

Manchester University

A persistent problem in understanding how the hypothetical internal clock underlying interval timing in humans might work is that the clock is usually supposed to be only the "front-end" of a complex timing system involving memory and decision processes in addition to the clock, where behaviour observed depends on the operation of the whole system. Two complementary approaches to research in this area are (i) to try to "isolate" parts of the system (e.g. the clock) leaving everything else intact, and (ii) to study the way in which the behaviour of the whole system varies across conditions. This paper illustrates both approaches using data from very recent work conducted at Manchester. Firstly, attempts were made to alter clock processes alone by experiments which exploited (a) arousal manipulations and (b) modality effects, including effects of irrelevant stimuli. Secondly, a large-scale study of individual differences in timing behaviour is reported, where nearly 100 subjects each performed on 7 different timing tasks. These were temporal generalization with short and long standards, verbal estimation, and threshold determination [stimulus timing]; production, reproduction, and internal tempo [motor timing]. Correlations between performance indices from the different tasks offer us some insight into the way that the clock/memory/decision structure of the proposed timing system behaves under different conditions.

Session A - Thursday 20 July 11.20-1 pm

Symposium: "Role of knowledge, logic & normative standards in human inference" (continued)

Warnings and inducements as argument

Valerie Thompson1, Jonathan Evans2 and Simon Handley2

1. University of Saskatchewan

2. University of Plymouth

In natural contexts, conditional statements are often used as part of an argument, wherein the conditional premise is used to invite a conclusion. This study examined inferences invited by conditional warnings and inducements. For example, a conditional warning of the form "if tuition fees are raised, then students will no longer be able to afford a university education", appears to invite the inference that "tuition fees should not be raised". Several paradigms were used to examine the suppositions that support the invited inference (i.e., that it is undesirable for students to be unable to afford university education), as well as the chain of logic that supports the invited inference (i.e., if p, then q; want not-q, therefore should not-p). Reasoners were asked a) which inferences followed, b) to generate rebuttals to the invited inference, and c) to evaluate rebuttals that were provided by the experimenter.

Alternatives, falsification, and mental models theory

Steven Newstead1, Simon Handley1 and Valerie Thompson2

1. University of Plymouth

2. University of Saskatchewan

In this experiment, we tested Mental Model Theory's assumption that reasoners construct alternative models of the premises in order to falsify putative conclusions. Participants completed a task designed to measure their ability to construct alternative representations of premises, as well as a syllogistic reasoning task. For the latter task, reasoners were asked to evaluate four types of conclusions: valid conclusions, highly accessible but invalid conclusions (i.e., those that are likely to be considered first as putative conclusions), inaccessible conclusions (i.e., those that are unlikely to be considered as possible conclusions), and impossible conclusions. Reasoners who scored well on the alternative representations task were more likely: a) to correctly accept valid inferences, b) to correctly reject the highly accessible, but invalid conclusions, and c) to correctly identify the inaccessible conclusions as being consistent with the premises. These findings are consistent with the assumption that falsify putative conclusions by searching for alternative representations of the premises.

(End of symposium)

The p-value fallacy: Why inferential statistics don’t describe results

Peter Dixon

University of Alberta

The methods of statistical inference were originally proposed as a mechanical procedure for drawing conclusions from data, but they are rarely used in that way. Instead, inferential statistics are typically used to describe results and how well they match different possible interpretations; scientists draw their own conclusions. This mismatch of methods and goals underlies many of the well-known logical fallacies and interpretive problems in the standard hypothesis testing framework. A better approach is simply to articulate those different possible interpretations and then to describe the match of those interpretations to the data using likelihood ratios. Such an approach provides, in a direct and intuitive form, precisely the information that is conveyed by p values, but without the distracting and problematic rhetoric involved in testing null hypotheses.

Dual task co-ordination versus task difficulty: Evidence from Alzheimer patients and healthy adults

R H Logie1, S Della Sala1, G Cocchini1 and A D Baddeley2

1. University of Aberdeen

2. University of Bristol

The ability of human beings to perform more than one thing at a time has long been a focus of study in the literature on human attention and on memory. However there is a continuing debate as to how the co-ordination of multiple tasks is accomplished, what kind of cognitive functions might be involved, and what determines success or failure in multiple task performance. Experiment 1 demonstrated that AD/pts, healthy elderly and young showed decrements in dual task performance even when each task constituted a very light cognitive load for the individual, but with much larger decrements shown for the patients. However patients were no more sensitive to increased task demand on single tasks than were healthy participants. These results might have arisen from the use of a memory task (span) together with a perceptuo-motor task (tracking). In Experiment 2, healthy adults performed either two memory tasks (visual pattern span and digit span), or a combination of each memory task with tracking. The largest dual task decrement was observed when visual pattern span was combined with tracking. The overall pattern is consistent with a multiple component working memory model, and an identifiable cognitive resource for dual task co-ordination that is insensitive to task difficulty.

A longitudinal study revealing age-related stability in dual-task performance

Margaret Crossley

University of Saskatchewan

Of 92 original participants in a dual-task study of normal aging, 40 were retested in 5-year and 10-year follow-up studies. Of these, 36 remained "healthy" and formed final samples of young (n= 9; ), middle-aged (n = 11), and older (n = 16) participants, with average ages of 40.6 (SD = 5.3), 63.1 (SD = 7.4) and 79.3 (SD = 4.6) years, respectively. At each study period, participants completed neuropsychological tests of memory and attention, and a dual-task study combining speeded finger-tapping with either "easy" (speech repetition) or "difficult" (letter generation verbal fluency) speaking tasks. Although the expected age group differences were evident, tests of memory remained remarkably stable across 10 years for the three age groups, while performance on measures of speeded visual attention declined for all of these healthy participants. Experimental data were analyzed in repeated measures ANOVA, with Age Group as the between- group measure and Study Period (original, 5-year, 10-year) and Task Difficulty ("easy" versus "difficult" speech tasks) as within group repeated measures. Single-task performance of speeded finger-tapping, speech repetition, and speech fluency declined across the 10-year study period for all age groups, and significant Study Period X Age Group interactions reflected greater loss across time for the older groups. As expected, interference during dual-task tapping (controlling for single-task performance) was greater for the oldest group at each test period, and was greater while concurrently performing the "difficult" speaking task compared to the "easy" speaking task. In contrast to expectations, interference did not increase across Study Period, and Age Group did not interact with Study Period or with Task Difficulty. These results suggest that speed of processing, but not attentional capacity, declines with age, at least as measured by these dual task data collected from healthy participants over a 10 year study period.

Session B - - Thursday 20 July 11.20-1 pm

Stimulus modality and the perception of empty time intervals in pigeons

Angelo Santi, Lori Ross and Andrew Miki

Wilfrid Laurier University, Ontario

Pigeons were trained to discriminate the duration (2 or 8 s) of an empty interval separated by two tone markers or by two light markers. Psychophysical testing indicated less sensitivity to empty intervals signalled by tone than by light. Pigeons judged the intervals marked by light to be longer than the same interval marked by tone. Training and psychophysical testing was carried out with empty intervals at target durations of 1 and 4 s, or 4 and 16 s. Pigeons continued to judge intervals marked by light to be longer than the same intervals marked by tone. The difference in the point of subjective equality for light and tone marked intervals was not constant across the different target duration sets. This suggests that the modality difference in the timing of empty intervals is not due to a difference in the latency to initiate timing.

Symposium: "Development of motion perception"

Organiser: Terri L Lewis

Processing of motion information in the primate cerebral cortex.

J Anthony Movshon

Howard Hughes Medical Institute at New York University, USA

A small group of areas in the primate cerebral cortex seems to be specialized for the processing of information about visual motion. Starting with signals from motion-sensitive cells in primary visual cortex, these areas contain a concentration of cells sensitive to motion. Motion-sensitive cells in V1 are primarily concerned with the representation of local first-order motion; this information is progressively elaborated by neurons in areas MT and MST into representations of global motion and optic flow. The outputs of MT and MST provide signals to areas responsible for perceptual judgements of motion and for the initiation of behavior dependent on motion information, such as pursuit eye movement.

While such key basic properties as directional selectivity appear very early in postnatal development and can be disrupted by some forms of visual deprivation, the maturation and sensitivity to environmental manipulation of more complex stages of motion analysis are not well understood at the neurophysiological level.

Interacting motion processing mechanisms in the developing infant.

Oliver Braddick, John Wattam-Bell, Alexandra Mason and Janette Atkinson

Visual Development Unit, University College London

We find no evidence from preferential looking (PL) of directionally selective processing before 7 weeks of age. However, directional mechanisms must underlie the newborn's optokinetic nystagmus (OKN) response. Parallel measurements of motion coherence thresholds, using OKN and PL, show that the two responses differ greatly in developmental course and sensitivity between 8-25 weeks of age.

These results are consistent with a model in which PL reveals the development of cortical motion processing, while neonatal OKN depends on a subcortical circuit, whose signature is temporal/nasal asymmetry in monocular OKN. Developmental changes in children with extensive unilateral lesions show that this initial subcortical asymmetry is modified by cortical-subcortical interactions.

Asymmetries also appear in evoked-potential (VEP) and PL responses. We find that the PL asymmetry follows the OKN asymmetry, while the VEP asymmetry is opposite. These relationships will only be understood in terms of developmental interactions between cortical motion processing and oculomotor mechanisms.

What does blindsight tell us about the functional architecture of motion perception?

Paul Azzopardi1, Mazyar Fallah2, Charles Gross2, Hillary Rodman3 and Alan Cowey1

1. University of Oxford

2. Princeton University, USA

3. Psychology Department and Yerkes RPRC, Emory University, USA

Patients rendered clinically blind as a result of striate cortex damage may nevertheless be able to discriminate stimuli presented in their field defects when forced-choice procedures are used. But there are conflicting reports as to whether or not the ability to discriminate motion is preserved. We recorded the responses to moving stimuli of neurons in areas MT and MST of monkeys with long-standing unilateral striate cortex lesions. Many neurons responded to the presence of movement in the scotoma, and some could discriminate the direction of single bars, but none could discriminate the direction of motion in random dot kinetograms depicting translation or motion-in-depth. Subsequently, we tested the ability of cortically-blind patients to discriminate the same stimuli, with the same results. Direction discrimination in the scotoma seems to be based solely on change in position, implying that motion processing per se is abolished. Blindsight therefore provides no evidence to support the proposed existence of a subcortical pathway to extrastriate cortex which bypasses striate cortex and which is specialised for analysing "fast" motion.

The perception of local and global motion after early pattern deprivation in humans.

Terri L Lewis1, 2, 3, Dave Ellemberg2, Daphne Maurer1,2, Nancy Defina2 and Henry P Brent1,3

1. The Hospital for Sick Children, Toronto

2. McMaster University

3. University of Toronto

We assessed the perception of local and global motion in patients who had been deprived of early visual experience by dense central cataracts. Despite years of visual experience after treatment, patients showed deficits on both tasks. Like our previous findings for contrast sensitivity, the deficits in sensitivity to local motion were comparable after either monocular deprivation (n = 10) or binocular deprivation (n = 9). Surprisingly, for global motion tested with random-dot kinematograms, coherence thresholds were nearly normal (M = 8.5%, n = 24) after monocular deprivation (M = 14%, n = 14) and significantly worse after binocular deprivation (M = 44%, n = 8). The unexpectedly good results after monocular deprivation suggest that normal input to only one eye reduces the deleterious effects of deprivation on the higher cortical areas involved in the perception of global motion. Thus, after monocular deprivation, competitive interactions occurring in the primary visual cortex may give way to collaborative interactions at higher neural centres enabling a relative sparing of at least some visual functions.

(End of symposium)

Session A - Thursday 20 July 2-4.20 pm

Temporal jitter disrupts speech intelligibility: Simulations of auditory aging

M. Kathleen Pichora-Fuller1, Bruce Schneider2 and Hollis Pass1

1. University of British Columbia

2. University of Toronto

Auditory temporal processing declines in aging adults may partially account for their difficulty understanding speech. To mimic such age-related declines, sentences were temporally jittered. Intact and jittered sentences were presented in babble to young listeners. For the signal x(t), the internal representation y(t) is modeled as a time-delayed version with delay d varying over time as y(t)=x[t-d(t)]. The first factor is the range of delays, modeled as the RMS of a band-limited noise. The second factor is rate of change of delays, modeled as the bandpass of a noise. Word recognition was unchanged when the second factor dominated (RMS = .05 ms, BW = 500 Hz), reduced slightly (10%) when the first dominated (RMS = .25 ms, BW = 100 Hz), and reduced greatly (50%) when both contributed (RMS = .25 ms, BW = 500 Hz). This is a first attempt to simulate temporal aspects of auditory aging.

Symposium: "Cognitive aging"

Organisers: Patrick Rabbitt and Fergus Craik

Age slows, and so sometimes obliterates consciousness of events.

Patrick Rabbitt

University of Toronto

After people make errors during simple continuous tasks they recognise them at some level because their sequent responses are slowed. People can correct nearly all of the errors that they make during simple continuous tasks by making the response that they should have made.Old age does not affect the efficiency of either of these forms of error detection and correction. However when people are asked to signal their errors by immediately making some other response they do so slowly and inaccurately, and the older they are the fewer responses they signal. When probed, they do not recall making errors. Nevertheless, even those errors that are not signalled are invariably followed by slow responses to sequent events. It seems that events that are not overtly acknowledged are still registered, but not remembered. Increasing the intervals between successive signals and responses improves performance, so that when these are as long as 2 sec error signalling is as efficient as error correction. The age difference in efficiency of error signalling disappears. We suggest that this means that simple events have successive, perhaps independent , representations which become serially available in time. During a fast paced task atention to new signals and responses prevents attention to later arriving representations. Because all cognitive processes are slowed by age older people need more time to become conscious that they have made an an error and to do something about it. Self-monitoring, even in simple tasks, is slowed by age, and thus becomes more vulnerable to the pace of events.

Aging and visual marking: Selective deficits for moving stimuli.

Elizabeth A Maylor and Derrick G Watson

University of Warwick

Previous research has shown that new visual information can be selectively prioritized by the top-down inhibition of old stimuli already in the visual field (visual marking; Watson & Humphreys, 1997). Moreover, the method of visual marking depends upon the properties of the old items such as their motion and the extent to which they can be grouped. We present three experiments to assess the effects of aging on visual marking. Experiment 1 examined performance with stationary items; Experiments 2 and 3 used moving stimuli. The results showed that visual marking was relatively unimpaired by aging for stationary stimuli. In contrast, there were age-related deficits in visual marking for moving stimuli, particularly when there was no feature difference between the old and new items. These differential effects of aging provide support for the deployment of different methods of visual marking depending upon the properties of the old (to-be-ignored) items.

Watson, D. G., & Humphreys, G. W. (1997). Visual marking: Prioritizing selection for new objects by top-down attentional inhibition of old objects. Psychological Review, 104, 90-122.

Adult-age differences in memory performance: Tests of an associative deficit hypothesis

Moshe Naveh-Benjamin

Ben-Gurion University of the Negev, Israel

An associative hypothesis to explain and predict older adults' deficient explicit episodic memory performance is outlined and tested. The hypothesis attributes a substantial part of older adults' deficient memory performance to their difficulty in merging unrelated attributes-units of an episode into a cohesive unit. While each of the components can be memorized to a reasonable degree, the associations which tie the attributes-units to each other grow weaker in old age. Four experiments are reported which provide: a) a converging validity to the hypothesis by demonstrating this associative deficit for both inter-item relationships and intra-item relationships, and b) a discriminant validity to the hypothesis, by contrasting and testing competing predictions made by the associative hypothesis and by alternative hypotheses. The implications of these results to older adults’ episodic memory performance are discussed.

Retrieval induced forgetting in normal aging.

Tim Perfect1, Chris Moulin2 and Martin Conway3

1. University of Plymouth

2. University of Reading

3. University of Bristol

In the field of cognitive aging it has been suggested that the cognitive deficits experienced by older adults stem from a general deficit in inhibitory function. In memory research, the retrieval-induced-forgetting paradigm has been used to isolate inhibitory processes that occur during retrieval. In a series of studies we examine whether there are age-related reductions in inhibition during memory retrieval. Younger and older adults were tested on a series of explicit and implicit tasks using the retrieval induced forgetting paradigm. None of the studies provide evidence in support of our predictions. These data suggest either that inhibitory effects are universal across the age range, or inhibitory mechanisms are not involved in retrieval. These two possibilities will be discussed.

Adult aging and planning ability

Louise Phillips and Mairi MacLeod

Aberdeen University

The formulation and execution of efficient plans is dependent upon the prefrontal cortex of the brain. Normal adult aging causes changes in the structure and function of the frontal lobes, but relatively little is known of the nature of age effects on planning. The current experiment looked at the effects of aging on a multistage task of party organisation in 96 participants aged between 16 and 79. Older participants showed poorer planning, and tended to make more rule breaks such as trying to buy items with insufficient funds. There were no age effects on other types of error, such as interpretation failuresor inefficiencies of task allocation. A qualitatively different pattern of errors was seen in young and older groups. These results can be contrasted with the pattern of age differences on a series of other tasks of planning (the Tower of London task, Multiple Errands test, and subtests from the Behavioural Assessment of Dysexecutive Syndrome). Overall, the results suggest that the nature and extent of age differences in planning vary considerably depending on such factors as: memory load, perceived importance of rules in the task, and planning complexity

(End of symposium)

Session B - Thursday 20 July 2-4.20 pm

Auditory attentional blink in the presence or absence of filler items

Sébastien Tremblay and Dylan M Jones

Cardiff University

Identification of the second of two targets in a rapidly presented sequence of stimuli is often incorrect when it falls within about 500 ms of the first target. Although the phenomenon of attentional blink (AB) is well-established in the visual modality, some claim that there is no AB for auditory sequences (Potter, Chun, Banks & Muckenhoupt, 1998) while others report a robust auditory AB (Arnell & Jolicoeur, 1999; Duncan, Ward & Shapiro, 1994). The present study provides more evidence that there is an effect of AB in the auditory modality. There was a significant deficit in target two report accuracy but it diminished as a function of the temporal lag between the two targets. The magnitude of the auditory AB was greater when there were filler items in between the targets but even in the absence of fillers the AB was significant. The auditory AB reported here was not due to task switching deficit as the same discrimination task applied for both targets.

Attention, occlusion, and previous experience

Jay Pratt and Allison B Sekuler

University of Toronoto

There is considerable evidence indicating that cueing a specific portion of an object results in the entire object being attended to. One goal of the present study was to determine whether attentional cueing effects act on objects defined only in terms of occlusion cues. The second goal was to determine whether previous experience with an object could halt perceptual (i.e., amodal) completion. In Experiment 1, two parallel rectangles were initially displayed and then the middle portions of these objects were occluded. Attentional cueing effects were found for both discrete portions of the completed rectangles. In Experiment 2, four discrete objects were initially displayed, followed by the same occluder used in the first experiment. The appearance of the occluder allowed the four discrete objects to be completed into two rectangles. Attentional cueing effects were found for the completed rectangles, indicating that previous experience may not be sufficient to halt the amodal completion of objects.

Spatial modulation of intramodal and crossmodal temporal processing deficits

S Soto-Faraco1,2, C Spence2, A Kingstone1 and J Duncan3

1. University of British Columbia

2. University of Oxford

3. MRC Cognition and Brain Sciences Unit, Cambridge

The attentional blink (AB) and repetition blindness (RB) effects both reflect costs in the processing of the second of two targets presented in a rapid sequence. The AB is a decrease in detection or identification accuracy on any target following the selection of a previous stimulus in a time window of 200 ms and 500 ms. The time course of AB often takes the form of a u-shaped function (produced by the so called lag-1 sparing). The RB reflects the cost in processing the second of two identical targets and its time course is linear (accuracy is inversely proportional to the temporal separation between targets). Although these two temporal processing deficits are similar in many ways, Chun (1997) demonstrated that they could be dissociated in terms of their differential sensitivity to target-distractor and inter-target similarity. We report a series of experiments in which we attempted to dissociate these effects in terms of their sensitivity to spatial uncertainty, and spatial displacement of the target stimuli. Pairs of targets (either the same or different) were presented from the same or different spatial locations in the same or different modalities. We found both visual and auditory AB and RB effects. Additionally we show that temporal processing deficits are modulated by spatial displacement between target stimuli.

Is perception, attention or action inhibited following spatial reorienting?

Raymond Klein, Bruce Dick, Jason Ivanoff and Tracy Taylor

Dalhousie University, Halifax

Immediately following a peripheral event there is a facilitation for the processing of nearby events. When shifts of gaze are not made this is said to reflect exogenous orienting of attention toward the source of stimulation. After attention is removed from such a source, there is impaired processing of subsequent, nearby events . The name originally given to this processing impairment, inhibition of return (IOR), implies that it is caused by removal of attention from the cued location and that its effect is to discourage attention from reorienting to the originally attended region of space. Despite this implication, whether perceptual, attentional or motor stages of processing are inhibited has been much debated. Recent evidence from our laboratory for effects of IOR on perception, attention and action will be used to illustrate the manifold nature of IOR.

A facilitatory effect does not contribute to the inhibition of return effect

Janice J Snyder1, William C Schmidt2 and Alan Kingstone3

1. University of Alberta

2. University at Buffalo, USA

3. University of British Columbia

It is well established that the "inhibition of return" (IOR) effect is found at a previously attended/cued location at long cue-target onset asynchronies. More recently, it has been reported (Pratt, Spalek, & Bradshaw, 1999) that in addition to the inhibitory effect at the cued location a co-occurring facilitatory effect occurs at the uncued location opposite to the attended/cued location. This finding led to the suggestion that facilitation at the uncued/opposite location may represent the primary component underlying IOR. In three experiments, we attempted to expand on these findings by defining the conditions necessary for observing the opposite facilitation effect. Our data revealed that unlike IOR, the opposite facilitation effect is fragile and weak, demonstrated by only a minority of subjects, and is statistically uncorrelated with the IOR effect. Together the data suggest that an opposite facilitation effect does not contribute significantly to the IOR effect.

Is task-set inhibition in set switching location specific?

Katherine Arbuthnott1 and Todd Woodward2

1. University of Regina

2. University of British Columbia

Set-switching tasks are used to study executive control processes involved in shifting attention between different goals. Costs attributable to task-switching are greater for alternating switches (ABA) than for non-alternating switches (CBA), an effect that is observed for perceptual and semantic judgment tasks, with manual or verbal responses (Arbuthnott & Frank, 2000; Mayr & Keele, 2000). In these investigations, stimuli were presented at a consistent location and the relevant task for each trial was cued verbally. The present studies examined switch costs for alternating and non-alternating series when the tasks were cued by spatial location. When tasks were uniquely associated with widely separated locations, switch cost was greater than with verbal cues but additional task-alternation cost was not observed. This suggests that different processes may be involved when switching among goals that have distinct locations versus goals that must be completed at a single location.

Is egocentric space automatically encoded?

Sandra Pouliot and Sylvain Gagnon

University of Quebec

Parkin, Walter and Hunkin (1995) suggested that egocentric space is automatically encoded. Using the criteria defined by Hasher and Zacks (1979), Naveh-Benjamin (1988) demonstrated that spatial information encoding was not an automatic process. However his spatial memory task probably emphasized encoding of allocentric space. In the present study, we tested Parkin et al's hypothesis using a task that was specifically designed to assess encoding of egocentric space. Five studies analyzing the effects of intent of memorization, dual task interference, old age, practice and individual differences were carried out using a computerized egocentric spatial memory task. Results show that old age and dual task interference impair egocentric spatial memory. However intent of memorization, practice and individual differences did not influence performance. The findings demonstrate that encoding of egocentric space is not a pure automatic process and therefore requires some cognitive effort.

Session A – Friday 21 July 9-10.20 am

Symposium: "Neuroimaging of memory"

Organiser: Roberto Cabeza

The role of the left prefrontal cortex in encoding of episodic memory

Paul Fletcher

Research Department of Psychiatry, University of Cambridge

A growing number of functional neuroimaging studies provide evidence for the importance of left prefrontal cortex (PFC) in episodic memory. The specific role of this region, however, remains unclear. Nevertheless, a number of characteristic features have emerged to suggest that the left PFC shows greater levels of activation when the encoding results in subsequent successful retrieval and when encoding occurs in association with a task which emphasises the semantic processing of studied material. With regard to the involvement in semantic processing demands, three related views have been described. It has been suggested that the left PFC activation reflects (i) the generation of semantic attributes of study material, (ii) the holding of those semantic attributes in working memory and (iii) the selection from among different semantic attributes. Distinguishing between these possibilities is difficult but it is suggested that a number of recent studies favour the latter interpretation. These studies will be reviewed.

Involvement of prefrontal regions on episodic memory retrieval: Mode, success, effort, and GRAM

Roberto Cabeza

University of Alberta

One approach to investigate the role of the prefrontal cortex (PFC) in episodic memory retrieval is to determine whether PFC activity remains constant (retrieval mode), increases (retrieval success), or decreases (retrieval effort) as a function of recovery. In an event-related fMRI study, we associated bilateral dorsolateral PFC with retrieval success, and left ventrolateral PFC with retrieval effort. Left PFC activity during episodic retrieval could reflect semantic processing. Since semantic processing is critical for the generation of candidate responses, left PFC activity should be more pronounced for recall, which requires generation, than for recognition, which does not. A PET study confirmed this prediction, and additionally revealed greater right PFC activity for recognition than for recall. To described this pattern we propose a generate/recognize asymmetry model (GRAM): left PFC is differentially more involved in generation processes than is right PFC, whereas right PFC is differentially more involved in recognition processes than is left PFC.

The functional organisation of working memory processes within the lateral frontal cortex.

Adrian M Owen

MRC Cognition and Brain Sciences Unit, Cambridge

Evidence is now converging to suggests that, at the area level, working memory processes within the dorsolateral and ventrolateral frontal cortices are organized according to the type of processing required, rather than according to the nature (i.e. modality), of the information being processed, as has been widely assumed. In a recent study using fMRI, performance of visual spatial and visual non-spatial working memory tasks was shown to involve identical regions of the lateral prefrontal cortex when all factors unrelated to the type of stimulus material were appropriately controlled. Moreover, recent positron emission tomography studies have demonstrated that either, or both, the ventrolateral and dorsolateral frontal regions can be activated in spatial, visual or verbal working memory tasks, depending on the precise (non-modality specific) executive processes that are called upon by the task being performed. The results provide further evidence that the mid-dorsolateral and mid-ventrolateral frontal cortical areas make distinct functional contributions to memory and corresponds with a fractionation of working memory processes in psychological terms.

Age-related differences in brain activity during memory

Cheryl L Grady

Rotman Research Institute, University of Toronto

Neuroimaging experiments have shown that brain activity patterns in older adults during performance of cognitive tasks differ from those seen in younger adults, even if their ability to do the task is not markedly different. Older adults have activation in many of the same areas as do young adults, but also have greater activity in other brain regions, particularly in prefrontal cortex. Various interpretations could be made of this finding, including compensatory mechanisms, or lack of inhibitory processes. In order to distinguish among these possibilities we need to determine how these age-related changes in brain activity are related to behavior in old adults, e.g. whether increased activity in a specific brain region occurs when task performance is spared in an older group or whether increased activity is associated with better or worse performance on a specific task. Recent experiments that shed light on this issue will be reviewed.

(End of symposium)

Session B - Friday 21 July 9-10.20 am

The resource demands of semantic priming

Eric Richards and Jennifer Stolz

University of Waterloo

The resource demands of semantic priming were examined in a series of experiments using a modified dual task paradigm. A prime word preceded a target stimulus, which was temporally paired with a tone. Participants were required to categorize the pitch of the tone prior to making a decision about the target stimulus (i.e., semantic classification or lexical decision). Using the logic that the resources required to process the target would limit those available for tone processing (Becker, 1976; Herdman & Dobbs, 1989), tone RTs were compared in related versus unrelated priming conditions to examine whether resource benefits are associated with semantic priming. The results are discussed in terms of the general theories of word recognition and the capacity constraints of attentional processing.

Binding action to a source: Evidence from Stroop priming

Bruce Milliken1, Juan Lupianez2, Karmen Bleile1 and Jason Leboe1

1. McMaster University

2. Universidad de Granada, Spain

Stroop interference is widely presumed to occur because of the predominance of word reading over colour naming processes. Consequently, priming of the color dimension might reasonably be predicted to reduce Stroop interference. In contrast to this prediction, we report the results of several experiments which demonstrate that priming of the color dimension speeds Stroop performance under some conditions, but slows Stroop performance under others. Attentional factors implicated in this processing flexibility are the focus of the experiments reported. The results are consistent with the view that priming introduces a source of influence on performance that can be difficult to discriminate from the normally fluent processing of the word dimension of Stroop stimuli.

Searching for threat

Jason Tipples1, Andy Young1, Philip Quinlan1, Paul Broks2 and Andy Ellis1

1. University Of York

2. University Of Sheffield

In a series of experiments, a modified version of the visual search task was used to test the idea that biologically-relevant threat stimuli might capture visuo-spatial attention. In Experiment 1, no overall reaction time or search rate advantage was found for angry faces compared to happy faces. In Experiment 2, however, there was evidence for both faster detection and search rates for threatening animals, compared to plants. Examination of the basis of this effect in Experiment 3, showed that it was not due to threat per se, since a detection and search rate advantage was also found for pleasant animals compared to plants. In Experiment 4, participants searched for the plants, pleasant and threatening animals used in Experiments 2 and 3, among a fixed heterogeneous selection of distractor items. There was no search rate or detection advantage for threatening animals compared to pleasant animals or plants. The same targets and distractors used in Experiment 4 were also used in Experiment 5. However, in Experiment 5, participants kept their eyes fixed on a central cross while searching for targets either close or distant from the fixation cross. There was no evidence for a ^Ìthreat¹ detection advantage either close or distant from the cross. We conclude that the visual search paradigm does not readily reveal any attentional biases that might exist for threatening stimuli.

Modulation of specific processes in task switching

Michael E J Masson, Daniel N Bub, and Todd S Woodward

University of Victoria

Task switching is typically assumed to involve executive control in coordinating the change in procedures as a function of change in task demands. A number of studies have examined general switch costs incurred in the performance of the second task as a consequence of having just carried out the first task. In contrast, we describe a process-specific influence of task switching on the performance of the first task. Considerable slowing is observed in the first task when that task shares specific operations with the second task. We have analyzed this phenomenon in the following situation: Task 1 requires reading aloud a word printed in black; Task 2 requires naming the color of a subsequent stimulus immediately following Task 1. On one block of trials, the stimulus in Task 2 is a row of colored asterisks and in another block it is a colored word. We find that word reading in Task 1 is substantially slowed when Task 2 involves colored words as opposed to colored asterisks. This effect does not obtain, however, when Task 1 requires a lexical decision rather than reading aloud, indicating that this modulatory effect is process specific.

Session C - Friday 21 July 9-10.20 am

Assessing inhibitory control in children and adults with a picture choice task

Sandra A Wiebe and James M Clark

Institute of Child Development, University of Minnesota, USA

Inhibitory control develops relatively late in childhood relative to other cognitive functions. Analysis of the development of inhibition would be facilitated by examining change in performance on one task across a wide age range. We have developed a task that is suitable for use with participants ranging from preschool-age to adulthood. Participants are presented with pairs of pictures and are asked to choose the picture that is related to a cue word on one of two dimensions (semantic or phonological). On half of the trials the incorrect picture choice is related to the cue word on the other dimension, and thus the choice of this response must be inhibited. Children show evidence of poor inhibitory control, making fewer correct responses on trials requiring inhibition. Adults successfully make the correct choice, but reaction times are lengthened when inhibition is required. These findings also have implications for our understanding of picture processing.

Intervention in early word learning: An experimental approach

Graham Schafer (Introduced by Professor D C Berry)

University of Reading

A lively debate in language development concerns the existence of stages in lexical learning. It is hypothesised that, before the attainment of certain 'principles', word learning is slow and effortful. As a corollary, infants' first words will be those most afforded by their immediate environment, and modification of the early lexicon (by intervention) will be difficult.

This study investigated modification of the early lexicon by parental intervention. Parents of nine-month-olds were given photographs of objects and animals, and were instructed to use these with their children, for 10 minutes per day, three times per week, in simple tasks (naming, matching, and sorting). After 12 weeks, infants' receptive comprehension was tested in a preferential looking task. Infants were instructed to look at images, which depicted novel exemplars of words from the training set. Infants in the experimental group looked at the images as instructed, while infants in a non-intervention control group did not. It is concluded that small amounts of training can modify early vocabulary. The theoretical implications of this are discussed.

Mismatch negativity and auditory backward recognition masking performance in people with a specific language impairment.

G M McArthur and D V M Bishop

University of Oxford

An influential hypothesis attributes the verbal problems of children with a specific language impairment (SLI) to an impairment in processing rapid or brief sounds. However, some studies have failed to demonstrate such a deficit. The rapid auditory processing skills of 16 people with an SLI and 16 people with normal spoken language skills were assessed with a modified version of Winkler, Reinikainen and Naatanen's (1993) paradigm to determine whether the discrepancies in the literature reflect differences in the sample studied, or methodological factors. This paradigm integrated mismatch negativity (MMN) and auditory backward recognition masking (ABRM) in four conditions that presented trials composed of a standard (25-ms 600-Hz) or deviant (25-ms 700-Hz) test tone followed by a 55-ms 1000-Hz backward masking tone after an interstimulus interval (ISI) of 20, 50, 150, or 300 ms. A fifth condition assessed frequency discrimination by presenting the standard and deviant test tones alone (i.e., without a backward masking tone). We will present data relevant to the rapid auditory processing deficit hypothesis, which predicts that the MMN component and ABRM performance of people with an SLI will be impaired in the short ISI conditions (i.e., 20 and 50 ms), but not the long ISI (150 and 300 ms) or frequency discrimination conditions.

"Yesterday I stroke a horse": Can children’s problems with verb morphology be explained in terms of a low-level auditory deficit?

Dorothy Bishop, Courtenay Frazier Norbury and Josie Briscoe

University of Oxford

Children with specific language impairment (SLI) have disproportionate difficulty with certain aspects of verb morphology. For instance, they frequently omit past tense –ed endings, though when they do produce such inflections they are used appropriately. Debate has centred on whether poor mastery of inflections is a secondary consequence of low-level auditory perceptual impairment, whether it reflects specific impairment in a specialised syntactic module, or whether the computational demands of inflectional morphology overload a limited processing capacity. The first of these possibilities is hard to accommodate with data we shall present comparing the performance of 19 children (aged 5; 9 – 10; 7) with mild–moderate sensorineural hearing impairment (SNH), 20 children with SLI (aged 7; 2 – 13; 0), and age-matched and language-matched groups of control children. On average the SNH group outperformed the SLI group and were comparable to controls. However, a minority of the SNH children were impaired on these tasks. These children were significantly younger than the rest of the SNH group, suggesting that acquisition of finite verb morphology may be delayed in children with hearing impairments, but they appear to catch up over time and do not show the persisting difficulties seen in SLI. Children with SLI demonstrated some ability to use past tense and 3rd person singular inflections correctly, and properties of verbs such as verb frequency and phonological complexity affected their ability to produce appropriate inflections, suggesting that their problems were not solely explicable in terms of syntactic factors, but may be influenced by other processing demands.

Session A - Friday 21 July 11-1 pm

Symposium: "Temporal lobe function in episodic and semantic memory"

Organisers: Karalyn Patterson and Kim Graham

Perceptual-mnemonic functions of the perirhinal cortex in macaques

Elisabeth A Murray

National Institute of Mental Health, Bethesda, MD, USA

The perirhinal cortex, a strip of cortex located in the ventromedial temporal lobe in macaques, plays a critical role in certain types of memory. The talk focuses on three aspects of the mnemonic contributions of the perirhinal cortex. First, the perirhinal cortex has been found to be essential for object recognition and for relating together the different sensory features of objects, thereby facilitating object identification. It carries out these functions even in the absence of the amygdala/hippocampus. Second, the perirhinal cortex serves as the final stage in a ventral visual cortical processing stream, known as the "what" pathway, that is devoted to the perception and identification of environmental stimuli. Its special contribution to this type of processing is held to be in the representation of complex conjunctions of features. Thus, the perirhinal cortex participates in acquisition, retrieval, and long-term storage of knowledge about objects, and, together with other cortical fields, also serves as a site of long-term storage of such knowledge. Third, the perirhinal cortex conveys already-processed information about objects to the hippocampus and amygdala, thereby allowing these structures to make different, secondary contributions to object memory, associating objects with events and affective valences, respectively.

Remote memory and the hippocampal complex in humans

Morris Moscovitch

University of Toronto at Mississauga

The studies address the question of whether the role of the hippocampal complex in memory is temporally-limited, needed only until memories are consolidated elsewhere, or whether it continues to contribute to storage and retrieval even of remote memories. Evidence will be presented from studies of people with hippocampal complex lesions, from a person with semantic dementia, and from neuroimaging studies in normal people that indicates that the hippocampal complex is needed for recollection of details of remote autoiographical episodes, public events, and even spatial memories, but not of semantic memories. The results call for a modification of traditional consolidation theory. A multiple-trace theory of memory ( Nadel and Moscovitch, 1997) provides a viable alternative.

Semantic dementia: A challenge to the multiple-trace model of memory consolidation?

Kim S Graham

MRC Cognition and Brain Sciences Unit, Cambridge

For many years, it has been thought that the hippocampal complex is only involved in the retrieval of recently experienced episodic memories. Evidence to support this view comes from patients with bilateral hippocampal damage who show better recall of distant memories compared to more recent personal events. An alternative theory proposes, however, that the hippocampus is important for the retrieval of all personal event memories, regardless of their age (Nadel and Moscovitch, 1997). Here, these two models of memory consolidation will be evaluated by reviewing neuropsychological data from semantic dementia: these patients, who have focal atrophy of the temporal neocortex with relative sparing of the hippocampal complex, have a relatively selective, yet progressive, loss of semantic memory. In support of a temporary role of the hippocampus in episodic recall, patients with semantic dementia show better retrieval of recent autobiographical memories compared to those from the more distant past. To account for these contradictory results, Moscovitch and Nadel (1999) have proposed a number of possible explanations: (1) too few replications of the data; (2) impaired strategic retrieval due to concomitant frontal damage; and (3) preserved non-verbal access to autobiographical memory. Further data from semantic dementia will be considered in order to address the possibility that one or other of these factors explains the observed advantage for recent personal events.


Moscovitch, M. and Nadel, L. (1999). Multiple-trace theory and semantic dementia: Response to K.S. Graham (1999). Trends in Cognitive Sciences. 3, 85-122.

Nadel, L. and Moscovitch, M. (1997). Memory consolidation, retrograde amnesia and the hippocampal complex. Current Opinion in Neurobiology. 7, 217-227.

Dissociations in cognitive memory: The syndrome of developmental amnesia.

Faraneh Vargha-Khadem1, David G Gadian1 and Mortimer Mishkin2

1. Institute of Child Health, University College London

2. National Institute of Mental Health, Bethesda, USA

The dearth of studies on amnesia in children has led to the assumption that when damage to the medial temporal lobe system occurs early in life, the compensatory capacity of the immature brain rescues memory functions. An alternative view is that such damage so interferes with the development of learning and memory that it results not in selective cognitive impairments but in general mental retardation. Data will be presented to counter both of these arguments. Results obtained from a series of 12 amnesic patients with a history of hypoxic ischaemic damage sustained perinatally or during childhood indicate that regardless of age at onset of hippocampal pathology, there is a pronounced dissociation between episodic memory, which is severely impaired, and semantic memory, which is relatively preserved. A second dissociation in these patients is characterized by impaired recall and preserved recognition. These findings are discussed in terms of the neuropathology associated with hypoxic ischaemic damage and a hierarchical model of cognitive memory.

(End of symposium)

Session B - Friday 21 July 11-1 pm

Crossmodal links in covert endogenous spatial attention between audition and touch

Donna M Lloyd

University of Manchester

Three experiments were designed to investigate crossmodal links in endogenous spatial attention between audition and touch, using the orthogonal spatial cuing paradigm. Participants discriminated the elevation (up vs. down) of auditory or tactile targets presented to either the left or right. Experiment 1, in which targets were expected on a particular side in just one modality, demonstrated that people could shift their attention around independently in either audition or touch. Experiment 2 demonstrated that when people were informed that targets were more likely on one side for both modalities, elevation judgments were faster on that side in both audition and touch. However, it was possible to ‘split’ auditory and tactile attention, when targets in the two modalities were expected on constant but opposite sides throughout a block. A final study with crossed hands suggests that audiotactile links in spatial attention apply to common external locations, rather than simply being determined by the hemisphere to which information initially projects. These results are discussed in relation to previous findings regarding audiovisual and visuotactile links in attention, and to their possible neural substrates.

Symposium: "Confidence in human judgement"

Organisers: Joseph V Baranski and Nigel Harvey

Moderation of base rate neglect by group discussion and range specification: A calibration study

Tim Rakow, Sarah Finer and Nigel Harvey

University College London

Medical students judged the likelihood that an applicant to medical school would receive an offer of a place on the basis of 8 cues. Participants were naïve to the task, though familiar with its context. In experiment 1 participants made individual judgements before and after group discussion. Consistent with the literature on lay judgement, participants were poorly calibrated and far less accurate than a logistic regression model. Poor calibration was largely attributable to considerable 'bias', with 'discrimination' being comparable to the statistical model. The simple provision of base rate information (the proportion of applicants receiving offers) had minimal impact upon the magnitude of bias of individual judgements. Bias was significantly reduced by group discussion when base rate information was provided (with no detriment to discrimination), but remained unaltered in the absence of base rate information. In experiment 2 some participants were provided either information concerning the distribution of probability estimates or the range of estimates generated by the statistical model. The participants receiving this information were well calibrated, and their accuracy was close to that of the logistic regression model. Results suggest our participants could identify and use appropriate cues, but needed assistance in the scaling of their response. Specifying a 'plausible range' for responses was sufficient to foster well-calibrated judgement. Extensive feedback or instruction in cue utilisation was not necessary in this instance.

The hard-easy effect in the calibration of subjective probabilities: The effect of

defining 'difficulty' in terms of absolute difference rather than familiarity

Alastair McClelland, John Haynes and Zhuo Jia Sun

University College London

Juslin (1993) obtained good calibration at different levels of performance when items were segregated on the basis of rated familiarity, rather than solution probability. In the present study, we report a partial replication and extension of Juslin's work. In the first experiment, participants were presented with a list of country names, and rated each country for familiarity. They were then given pairs of country names (selected at random) and had to decide which country had the bigger land area. For each pair, a half-scale confidence rating was also requested. The items in each domain were then split into two categories on the basis of either average familiarity (following Juslin) or absolute difference in land area. With familiarity, the hard-easy effect was abolished, but with absolute difference a hard-easy effect was still observed. In a second study, we explicitly presented participants with the absolute difference information for each pair of countries to investigate whether or not this would abolish the hard-easy effect. The results are discussed with respect to ecological and cognitive-bias accounts of calibration performance.

Judging confidence influences decision processing

William M Petrusic1 and Joseph V Baranski2

1. Carleton University, Ottawa

2. DCIEM, Toronto

We examined the effects of rendering confidence judgments on the properties of the decision process in sensory-perceptual and general knowledge tasks. The requirement of confidence judgments substantially increases decisional response times and, generally, the increase is inversely related to the difficulty of the judgement. When confidence is rendered, discriminative accuracy may also be impaired; although these effects are small in absolute terms, the relative decreases in accuracy are large and are an inverse function of decision difficulty. Finally, in a sensory detection task, we found that decision times increased with the number of confidence categories used (two, four, or six) and the increases in decision time were the largest when detection was easiest. Taken together, these experiments implicate both decisional and post-decisional loci for the basis of confidence and they permit rejection of the view that the confidence-based increases in decision time arise as a consequence of a slowed rate of evidence accumulation due to dual-task processing.

Explaining extreme overconfidence on interval questions

Jack B Soll1 and Joshua Klayman2

1. INSEAD, Fontainebleau, France

2. University of Chicago, USA

Overconfidence depends significantly on how questions are asked. For example, people are only mildly overconfident on binary choice questions, but they are tremendously overconfident on interval questions (Klayman, Soll, González-Vallejo & Barlas, 1999). In our current research, we develop a random error model for intervals to help explain this extreme overconfidence. The basic idea is that if people are unreliable in how they set interval limits, that should translate to greater uncertainty and wider intervals. People will be overconfident to the extent that they fail to account for variation in the way that they set the limits. In addition, we hypothesize that interval questions are more susceptible to confirmation biases, because the alternative hypothesis is not as salient as in binary choice questions. We use models, simulations, and experiments to illustrate and test these propositions.

Subjective probability in the assessment of threat: Comparing expert vs. novice use of inconclusive information

Joseph V Baranski1 and William M Petrusic2

1. DCIEM, Toronto

2. Carleton University, Ottawa

This study examined how people use inconclusive information when forming subjective probability assessments using a medium fidelity Naval threat assessment simulation. In the present context, inconclusive information refers to data that is relevant but does not clearly support a decision alternative. On each of 36 trials, subjects interrogated 10 pieces of information (e.g., speed, direction, bearing) about 'targets' in a radar space. The amount of hostile (n(H)), peaceful (n(P)), and 'inconclusive (n(I)) information was factorially varied across targets. For novices (i.e., civilian university students), inconclusive information "dilutes" threat assessments; i.e., when in doubt, civilians conservatively err on the side of "friendly". For experts (i.e., senior OPs room officers), inconclusive information is ignored, except when the difference between n(H) and n(P) is small; i.e., when in doubt, military experts conservatively err on the side of "foe". Subjective probabilities in the assessment of threat are best fit by a model that includes a component based on the 'balance of evidence' [i.e., n(H) - n(P)] and a component based on the scaling of doubtful evidence [i.e., n(I)].

(End of symposium)

Session C - Friday 21 July 11-1 pm

The spatial tuning of human auditory perceptual channels under binaural and monaural conditions

Susan E Boehnke and Dennis P Phillips

Dalhousie University, Halifax

Human sound localization is acute for frontal locations and poorer in the lateral hemifields. The tuning of the perceptual channels for auditory space that underlie this acuity has not previously been examined. We have measured this tuning by exploiting a "between-channel" gap-detection paradigm in which detection thresholds for a silent interval (gap) were obtained when the leading and trailing noise markers of the gap were disposed at various absolute locations and separations throughout 360 degrees of azimuth, under binaural and monaural conditions. The binaural results indicate there are two, broadly-tuned hemifield channels whose medial borders overlap through the midline. The monaural results were systematically different, confirming the spatial channels were due to binaural processes. These results are compatible with data on the spatial receptive fields of cortical auditory neurons, and they provide a framework which may explain the localization acuity of human listeners, as well as some spatial masking and attentional phenomena.

The effect of spectral slope on infants' discrimination of timbre

C D Tsang and L J Trainor

McMaster University

Different speech sounds, voices, and musical instruments differ in spectral slope (the rate at which intensity falls off with frequency), and their spectral slopes cluster around -6 dB/octave. If spectral slope is important in timbre perception, enhanced sensitivity would be expected for spectral slopes near -6 dB/octave in comparison to spectral slopes very different from this value. Spectral slope discrimination was tested in 8-month-old infants across a range of spectral slopes (-16 vs. -10; -10 vs. -4; -3 vs. +3; +4 vs. +10; and +4 vs. +16 dB/octave) using a conditionedhead turn procedure. Infants only showed discrimination between -10 and -4 dB/octave. This suggests that the auditory system is tuned to sounds in the range of real-world spectral slopes very early in life.

Hierarchical processing in the auditory cortex? fMRI mapping of responses to spectral and temporal complexity

D A Hall1, I S Johnsrude2, M S Gonçalves1, M P Haggard1, A R Palmer1, A Q Summerfield1, M A Akeroyd1 and R S J Frackowiak2

1. MRC Institute of Hearing Research, Nottingham

2. Wellcome Department of Cognitive Neurology, London

The present study tested the hypothesis that processing in primary and secondary auditory areas is hierarchical: complex acoustic stimuli should activate secondary auditory regions more strongly than do simple stimuli. We used a 2x2 factorial design created by crossing spectral complexity (harmonic complex with F0=186 Hz vs single tone at 500 Hz) and temporal complexity (frequency modulated at 5 Hz vs static signal). Signals were presented diotically through electrostatic headphones to 6 normally-hearing volunteers. Functional and structural images were acquired using a 2T Magnetom VISION MRI system. The 4 conditions were analysed using a fixed-effects multi-subject model (SPM99).

There were significant main effects of both spectral and temporal complexity (P<0.05). Both modulation vs static and complex vs single tone contrasts produced activation bilaterally in the primary auditory area and immediately adjacent secondary auditory areas: activation was largely additive (no significant areas of interaction). These main effects broadly co-localised, but the region responsive to temporal complexity was the more extensive. Responses to temporal complexity alone were found in additional areas bilaterally in the superior temporal sulcus (STS) and in a region anterior to the primary auditory area on the supratemporal plane (AA). Additivity may suggest an increasing auditory response to complexity. However, support for hierarchical processing is limited because effects of spectral and temporal complexity occurred in both primary and secondary areas. The specificity of the response in STS and AA to temporal complexity merits further investigation.

Subsystems in the human auditory cortex - evidence from functional neuroimaging studies

Sophie K Scott1, Stuart Rosen2, Catrin Blank3 and Richard J S Wise3 (Introduced by James Blair)

1. Institute of Cognitive Neuroscience, University College London

2. Department of Phonetics, University College London

3. MRC Cyclotron Unit, Hammersmith Hospital

Work in visual neuroscience has identified at least two possible functional subsystems in visual processing, a ventral 'what' pathway passing from visual cortex to the ventral temporal lobes and a dorsal 'where/how' pathway passing from visual cortex to the parietal lobes. Work in non-human primates has revealed analogous pathways in the auditory system. Using speech stimuli of varying intelligibility but equivalent structural complexity, and functional neuroimaging (PET) we demonstrate a stream of processing in the human left temporal lobe associated with the intelligibility of speech The left superior temporal sulcus responds to the presence of phonetic information, but its anterior part only responds if the stimulus is also intelligible. This novel observation demonstrates a left-lateralised anterior temporal pathway for speech comprehension. We propose that this forms part of a verbal 'what' pathway in human auditory perception. The right temporal lobe, in contrast, showed selective activation for stimuli that contained dynamic pitch variation, regardless of intelligibility.

Multisensory coding: Implications of findings on tactile illusions

Susanna Millar and Zainab Al-Attar

University of Oxford

The similarity of errors in touch to 'optical' illusions for T-shapes and Müller-Lyer figures presents a paradox that is not resolved by modality-specific nor by cognitive mediation theories. Tactile shape perception depends on inputs from touch, movement and body posture cues, in the absence of vision. Nevertheless, the vertical line is overestimated in inverted T-shapes and underestimated in rotated T-shapes, as in vision. Similarly, the shaft of figures with converging fins is perceived as smaller by touch than in divergent fin figures. We argue that the illusions can be explained by disparities in spatial reference cues from all sources, which normally converge (coincide) in accurate perception. We show that vertical errors in T - shapes are predicted by the locations of the additional junction point on segmented lines, and that the illusion is reduced significantly by two-handed scanning relative to an external frame and to egocentric cues. The Müller-Lyer illusion is explained by disparities between cues to shape and length from the fin and shaft elements within the shapes. Instructions to ignore the fins had no effect in vision in the presence of allocentric cues, but no movements relative to egocentric cues. The tactual illusion was almost eliminated by instructions to relate scannin movements to egocentric cues and to ignore the fins. The hypothesis, that length illusions in touch and vision depend on disparities in current spatial reference information, accounts for similarities and differences between the visual and tactual illusions by assuming that accurate perception in both modalities depends on congruent reference cues from all sources.

How does the brain solve the crossmodal binding problem? Insights from fMRI studies of audio-visual and visuo-tactile integration.

Gemma Calvert

University of Oxford

The integration of information from different sensory channels markedly enhances the detection and identification of objects and events in the environment. Semantically and/or spatially congruent multisensory inputs speed discriminations and improve reaction times compared to the response to any single modality in isolation. Incongruent inputs have the opposite effect, hampering classification and slowing responsiveness so that erroneous binding is prevented. These behavioural features of crossmodal processing appear to have parallels in the response properties of multisensory integrative cells in the superior colliculus in lower mammals. Spatially concordant multisensory inputs result in a substantial, often multiplicative (i.e. greater than the sum of the individual inputs) response enhancement; discordant inputs can produce a profound response depression. At present, it is not known whether a similar method of intersensory integration onto multisensory neurons applies to humans, or for the integration of complex inputs relating to stimulus identity, as well as stimulus location. This question has now been addressed in a series of experiments using fMRI. In the first series of experiments, subjects were exposed to alternating epochs of congruent and incongruent audio-visual (speech and non-speech) inputs and to each modality in isolation. In a second series of experiments, subjects were scanned whilst presented with spatially concordant or discordant visuo-tactile inputs (vibro-tactile stimulation and LED's) whilst attention to one or modality was manipulated by the response instructions. The results of these studies provide clear neurophysiological evidence of crossmodal binding by convergence onto multisensory cells in human heteromodal cortex. They further suggest that response enhancement and depression may be a general property of multisensory integration operating at different levels of the neuroaxis and irrespective of the purpose for which sensory inputs are combined.

Session A - Friday 21 July 2-3.20 pm

Symposium: "Parietal lobe in vision and visuomotor control"

Organisers: Melvyn A Goodale and A David Milner

Frames of reference and timing in the visual control of skilled actions.

Melvyn A Goodale and Yaoping Hu

MRC Group on Action and Perception, University of Western Ontario

We recently examined the frames of reference used by normal subjects to scale their grasp when picking up objects of different sizes. When faced with a target object and a distractor that was either larger or smaller than the target, it did not matter which distractor the target was paired with: the grasp was scaled to the real size of the target object and was not affected by the presence of the other object. When subjects picked up the target after a 5-s delay during and after which the target was no longer visible, a significantly larger grip aperture was observed when the target had been paired with a smaller object, than when the same target had been paired with a larger object. Exactly the same effect was observed when subjects simply gave a ‘perceptual’ estimate of the target’s size – even when the target was visible. These results suggest that normal (real-time) visuomotor control relies on real-world metrics whereas delayed grasping utilizes the same relative (scene-based) metrics used by conscious perception. This result converges nicely with previous experiments on the visual-form agnosic patient D.F. who shows completely normal scaling of her grasp in real time but loses all scaling when a 2 s delay is introduced between viewing the object and making the movement. D.F. presumably can use visuomotor networks in her intact parietal cortex to program real-time actions but cannot use stored perceptual representations to drive a grasp ‘off-line’.

Two routes from vision to action: Effects of bilateral posterior parietal damage.

A David Milner1 and H Chris Dijkerman2

1. University of Durham

2. University of Utrecht, Netherlands

Goodale and colleagues showed some years ago that the visual-form agnosic patient D.F. was quite unable to retain the visual dimensions of objects when required to withhold response for a few seconds in order then to make a 'pantomimed' response in the absence of the object. We later found that D.F. even has difficulties in directing her eyes or hand to the location of an LED after a few seconds of delay. These observations fit with the idea that making a pantomimed response requires that explicit perceptual representations be used to guide action ‘off-line’, a capacity that D.F. no longer possesses because of her brain damage. We have recently studied two patients with Balint-Holmes syndrome, resulting from bilateral posterior parietal damage, to seek complementary evidence for this 'indirect' route from vision to action. These patients show 'optic ataxia'; that is they are impaired in the direct visuomotor control of actions such as reaching and grasping. We have found, however, that they show paradoxical improvements in their visuomotor control when making pantomimed rather than direct responses to target objects, in both the spatial and size domains. This is consistent with the idea that they can use a relatively well-preserved 'perceptual' route to action. We also found evidence that one of the patients spontaneously developed a 'perceptual' strategy to overcome her visuomotor difficulties.

How does the posterior parietal cortex control visually guided actions?

Michel Desmurget.

Psychophysique et Neuropsychologie Espace et Action, INSERM Unité 94, Bron, France.

Numerous studies have indicated that the posterior parietal cortex (PPC) is critically involved in the execution of visually-directed movements. Although PPC involvement in planning processes has been emphasized in the past, it was often suggested that this area may also be involved in on-line movement control. In this talk I shall provide direct evidence supporting this view. Based on recent studies involving neuroimaging, transcranial magnetic stimulation, and brain damaged patients, I shall defend the idea that PPC (1) generates an internal representation of the instantaneous hand location by integrating the motor outflow and sensory inflow (forward model), (2) computes a dynamic motor error by comparing the estimated state of the hand location with the location of the target.

Visually guided grasping produces fMRI activation in human anterior intraparietal sulcus.

Jody C Culham1, Rieko Osu1, A David Milner2, Joseph S Gati1, Ravi S Menon1, and Melvyn A Goodale1.

1. MRC Group on Action and Perception, University of Western Ontario.

2. University of Durham

We used functional magnetic resonance imaging (fMRI) to examine the human neural substrates of visually-guided grasping. Within the relatively wide bore of a 4 Tesla magnet, subjects directly viewed (without mirrors) a rotating drum, which presented rectangular plexiglas blocks of varying length and orientation. On each trial, a single target was illuminated and the subject reached towards the object and grasped its edges with a precision grip (using the index finger and thumb). In a control condition, subjects reached and touched but did not grasp the target object. Event-related single trials took advantage of the haemodynamic delay to dissociate true grasping activation from motion artifacts. Grasping produced higher activation levels than reaching in a region of anterior intraparietal (AIP) cortex. This area is a likely human homologue of monkey AIP, an area containing neurons which fire in preparation for grasping. In addition, several other parietal and occipito-temporal regions showed grasp-related activation. Thus we have found a reliable paradigm which allows us to identify human AIP and other grasping-related regions. This will allow us to conduct future experiments comparing grasping to other tasks such as object perception (with no motor component), grasping imagery, and delayed grasping.

Session B - Friday 21 July 2-3.20 pm

Symposium: "New research on human motivations for alcohol use"

Organiser: S H Stewart

Adolescents' motives for cigarette smoking and marijuana use: Factor structure and relations to motives for alcohol use

N Comeau, S H Stewart, P Loba, E Rhyno and H L Loughlin

Dalhousie University, Halifax

The present study was designed to test the utility of extending Cooper's (1994) 2 x 2 (valence x source) drinking motives model to adolescents' use of cigarettes and marijuana, and to examine the degree of correspondence of specific substance use motives across three different drugs (i.e., alcohol, cigarettes, and marijuana). Of a sample of 508 adolescents (239 females, 269 males; M age = 15.1 years), 312 (61.4%) reported alcohol use (M = 6.7 drinks/week), 192 (37.8%) reported smoking (M = 40.3 cigarettes/week), and 154 (30.3%) reported use of marijuana (M = 6.1 marijuana cigarettes/week). Factor analytic and multiple regression results support Cooper's four-factor model of drinking motives, and suggest that this model may also be applied to adolescents' reasons for smoking and marijuana use. The results further suggest that there are some similarities in adolescents' specific motives for substance use across different drugs, particularly between motives for alcohol and marijuana.

Relations of drinking motives to promotion- and prevention-focus in other behavioral domains

S H Stewart1, C J Roney2, D R Lehman3, L Chung3, N Lawson3 and A Mueller3

1. Dalhousie University, Halifax

2. Kings College, Ontario

3. University of British Columbia

We examined whether positive (Enhancement; Social) and negative (Coping; Conformity) drinking motives (Cooper, 1994) relate to promotion- or prevention-focused self-regulation (Higgins, 1997) in the domains of social interaction and academic achievement. In four multiple regressions, we used 158 undergraduates' drinking motives scores to predict levels of promotion- and prevention-focus in social and academic domains, respectively. Positive and negative emotional drinking motives in Cooper's model (cf. Cox & Klinger, 1990) related more broadly to promotion- and prevention-focus, respectively, in domains other than drinking. Those who drink to increase positive emotions report a promotion-focus in their orientation toward social interactions and academic achievement (striving to increase affiliation/success). Those who drink to avoid negative emotions report a prevention-focus in their orientations toward social interactions and academic achievement (striving to avoid rejection/failure). Results suggest that people differ in their general proclivities to either approach pleasure or avoid pain across a variety of behavioral domains.

Relations between four personality risk factors for alcohol abuse and reinforcement-specific motives for drinking in non-alcoholic and substance abusing samples

P J Conrod1, P Woicik1, S H Stewart2 and R O Pihl3

1. State University of New York at Stony Brook, USA

2. Dalhousie University, Halifax

3. McGill University

Four personality characteristics (anxiety sensitivity; introversion/hopelessness; sensation seeking; impulsivity) discriminate between subtypes of substance abusers who demonstrate patterns of dependence on drugs that possess specific reinforcing effects (Conrod et al., in press). Since alcohol possesses a number of different reinforcing properties, we hypothesized that these personality risk factors should also be associated with self-reported reasons for alcohol use that are reinforcement-specific. 300 substance abusing women and 450 male and female undergraduates completed the Drug Abuse Subtyping Scale (Woicik & Conrod, 1999) and Drinking Motives Questionnaire (Cooper et al., 1992). Results were almost identical across the clinical and non-clinical samples. Anxiety sensitivity and hopelessness were specifically related to drinking motives involving coping with negative emotion. Sensation seeking was associated with drinking for social and enhancement effects. Impulsivity was associated with drinking for both positive and negative reinforcement. Results are discussed within the context of a four-factor model of drug abuse vulnerability.

Motivational patterns as predictors of alcohol use and the likelihood of change

W M Cox

University of Wales, Bangor

In a series of three studies, the Motivational Structure Questionnaire (MSQ) was used to predict alcohol consumption and motivation for change. The MSQ identifies respondents' salient concerns in various life areas, and the characteristic manner in which they strive for goals to resolve their concerns (i.e., their motivational structure). Participants in the three studies were college students or patients with alcohol abuse. Across the three studies, respondents with high scores on an "adaptive" motivational factor felt committed to goal pursuits from which they expected to derive emotional satisfaction, and they felt optimistic about succeeding. The adaptive factor was a significant negative predictor of (a) the amount of alcohol that the college students habitually consumed, (b) alcohol abusers' denial of a problem, and (c) the amount of alcohol that alcohol abusers drank one year following treatment. The adaptive factor was also a significant positive predictor of alcohol abusers' readiness for change.

(End of symposium)

Session C - Friday 21 July 2-3.20 pm

PCA network models of memory and perceptual processes: A matter of style

John R Vokey1, Jason M Tangen2 and Kevin Eva2

1. University of Lethbridge

2. McMaster University

The ability of people and animals to demonstrate tacit sensitivity to the structure of the environment around them is explored in terms of a simple PCA network model applied to pixel-maps of natural and artificial images. The eigenvectors obtained from the singular value decomposition of sets of these pixel-maps provide for descriptions of the stimuli in terms of visual "macro-features". These macro-features provide a simple basis not only for recognising previously-experienced images, but for the successful discrimination of novel images into various natural and artificial structural categories. A summary of simulations of the performance in various focal domains of humans (e.g., face categorisation/recognition, artificial grammar learning, EKG diagnoses), pigeons (natural categories, artists' paintings), and chimpanzees (kin recognition) is provided. The results suggest both that the eigen-decomposition is a necessary first-step, and that the discrimination is best seen as a judgement of the "style" of family-resemblance structures.

Categorization and the "Ratio Rule

A J Wills (Introduced by I P L McLaren)

Cambridge University

Many modern theories of categorization are based on the production of magnitude terms which represent the subjective level of evidence for a presented stimulus being a member of a particular category. Almost universal amongst such theories is the assumption that magnitude terms may be translated into response probabilities by the Ratio Rule (a.k.a. the Choice Axiom - Luce, 1959). Through the presentation of a number of categorization experiments, a case is made that the Ratio Rule is an inappropriate formulation. It is suggested that theorists should employ a different type of Thurstonian choice process.

Luce, R. D. (1959). Individual Choice Behavior. New York: John Wiley & Sons

Relation between perceptual and informational learning of family resemblance structures

Lee R Brooks and Sam D Hannah

McMaster University

In the learning of both medical and artificial materials, explicit rules commonly function to name the objects of perceptual learning rather than to give sufficient conditions for identification. Subjects in experiments with artificial materials search for informational commonalities even when the identification task is incidental to the apparent main purpose of the experiment. However, the rules so generated do not describe their dependence on particular perceptual manifestations. A comparable phenomenon is observed in learning to apply medical rules. The standard, authoritative rules are clearly useful in learning to identify medical disorders in visual areas (ECG, patient appearance, dermatology), but they do not describe the dependence on particular perceptual manifestations that is acquired during the course of learning. The influence on these phenomena of family resemblance structure, featural ambiguity and confidence in rule application will be discussed.

The under-weighting of implicitly generated alternatives

Kevin W Eva and Lee R Brooks

McMaster University

A highly robust finding in the study of subjective probability judgments is that the rated likelihood of a hypothesis depends on the other hypotheses suggested (called the unpacking effect by Tversky and Koehler, 1994). For example, the rated probability that a randomly selected person might die of cancer tends to be greater when cancer is considered by itself than when presented in a list of potential diagnoses. Our previous work has shown, somewhat counter-intuitively, that the alternative diagnoses that have the greatest influence on the probability rating of a focal diagnosis are those that were most likely to have been considered implicitly (Eva, Brooks, Cunnington, and Norman, Submitted). This result suggests that participants under-appreciated diagnostic alternatives that they themselves generated relative to those that were explicitly presented. The current study was designed to demonstrate this same result for alternatives the participants themselves claim to have actually considered. We used clinical cases previously shown to have two highly likely and roughly equiprobable diagnoses. Second year medical students viewed either one or both of these diagnoses and were asked to rate them. They were then asked whether they had been considering a diagnosis that was not presented and if so what it was. A week later they were shown the original cases and asked to rate the original alternative(s) together with the alternative they had generated. The unpacking effect was found even when the diagnostic alternative that is unpacked is one that they claim to have considered while originally viewing that case. That is, they rated the originally presented diagnosis as less probable when the alternative they had claimed to be considering implicitly was explicitly presented. Furthermore, patient management strategies, such as requesting diagnostic tests, were affected in addition to pure probability ratings. Possible reasons for this under-appreciation of self-generated diagnoses will be discussed.

Session A - Friday 21 July 4-5.20 pm

An associative learning model of the illusory correlation effect

Robin A Murphy and Stefanie Schmeer

University of Hertfordshire Hatfield

Social psychologists have offered several hypotheses to explain the formation of stereotypes. One perspective is that they are the consequence of a perceived illusory correlation between group membership and certain behaviours. Hamilton and Gifford (1976) proposed that the infrequency of minority groups make them distinctive, thereby distorting people's perception of the relationship between group membership and behaviour. A modification to the Rescorla-Wagner (1972) model can also predict this effect by simply assuming that stimuli 1) acquire associations when presented together 2) associations representing stimuli that are not present on a given trial are also updated (Van-Hamme & Wasserman, 1994). One of its unique predictions is that the distorted perception should emerge preasymptotically before eventually diminishing. We report an experiment in which subjects were presented with vignettes describing members of either Group A or Group B performing either 'good' or 'bad' behaviours. The ratio of good/bad behaviours was always equivalent for members of both groups, but subjects experienced twice as many instances of group A members. The strength of the illusory correlation between group membership and good behaviour was assessed after either 18, 36, 54, or 72 trials. Results supported the predictions of the modified Rescorla-Wagner model.

Hamilton, D.L. & Gifford, R.K. (1976). Illusory correlation in interpersonal perception: A cognitive basis of stereotypic judgements. Journal of Experimental Social Psychology, 48, 5-17.

Rescorla, R.A. & Wagner, A.R. (1972). A theory of Pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. In A.H.Black & W.F. Prokasy (Eds.), Classical conditioning II: Current theory and research (pp. 64-99). New York: Appleton-Century-Crofts.

Van-Hamme, L.J. & Wasserman, E.A. (1994). Cue competition and causality judgment: The role of the nonpresentation of compound stimulus elements. Learning and Motivation, 25, 127-151.

Associatively mediated anti-generalisation in memory

I P L McLaren

University of Cambridge

Consider two stimuli, A and B, whose representations are associatively linked such that presentation of one stimulus retrieves a representation of the other. If we now present A what happens to the representation of B after retrieval? A straightforward analysis might have it that whatever happens to the representation for A (perhaps association with some outcome) will also happen to B, though perhaps to a lesser extent. This would constitute a form of generalisation between A and B mediated by the associations between them. Another analysis, suggested by recent research on retrospective revaluation effects in humans and infra-humans (e.g. Dickinson and Burke, 1996), would predict that whatever happened to the representation of A the opposite might be expected for the representation of B. Thus, if an association between the representation for A and some outcome were strengthened, then it should be weakened in the case of B. We might term this associatively mediated anti-generalisation.

The research reported here focuses on the latter phenomenon, but in memory rather than learning. Using a same / different recognition task with human subjects, I first demonstrate that, under certain circumstances, the effect of associatively retrieving a stimulus representation is the opposite to that which occurs on presentation of the stimulus. Then I consider to what extent this effect aligns with the retrospective revaluation literature referred to earlier.

Dickinson, A. & Burke, J. (1996). Within-compound associations mediate the retrospective revaluation of causality judgements. Quarterly Journal of Experimental Psychology, 49B, 60-80.

Two new forms of retrospective revaluation in human contingency learning.

Jan De Houwer (Introduced by Dr David Shanks)

University of Southampton

When a compound cue AT is followed by an outcome (AT+), human participants will judge the relation between cue T and the outcome to be less strong if A alone was previously paired with the outcome (A+). According to the probabilistic contrast model, such blocking effect is due to the fact that the A+ trials allow one to infer that A on its own is sufficient to explain the occurrence of the outcome on the AT+ trials. However, this conclusion is only justified if (a) A+ trials are treated as trials on which A and the outcome are present but T is absent and if (b) A is not accompanied by another predictive cue on the A+ trials. I report the results of two experiments which support the hypothesis that retrospective inferences about the status of T and other alternative cues on the A+ trials influence the contingency judgements for cue T. These findings support the probabilistic contrast model but are incompatible with the (revised) Rescorla-Wagner and SOP models.

Normative and descriptive accounts of the influence of power and contingency on causal judgment

David R Shanks1 and J Perales2

1. University College London

2. University of Granada, Spain

The Power PC theory (Cheng, 1997) predicts that causal judgments are based on causal power p of a potential cause, where p is the cause-effect contingency normalized by the base rate of the effect. Previous reports have demonstrated that both cause-effect contingency and effect base-rate independently affect estimates in causal learning tasks. In the present work these effects are replicated in three experiments. In Experiment 1, causal strength judgments were directly related to power p in a task in which the effect base-rate was manipulated across two positive and two negative contingency conditions. However, in Experiments 2 and 3 contingency manipulations affected causal estimates in several situations in which power p was held constant, contrary to the Power PC theory's predictions. This effect cannot be explained by participants' conflation of reliability and causal strength, as Experiment 3 demonstrated independence of causal judgments and confidence. Neither the Power PC theory nor the Rescorla-Wagner model can account for the entire pattern of results. However, the data are compatible with Pearce's (1987) model, as well as with the Belief Adjustment model (Catena, Maldonado, & Cßndido, 1998).

Session B - Friday 21 July 4-5.20 pm

Motor activation and inhibition elicited by masked primes: A threshold model and experimental evidence

Friederike Schlaghecken and Martin Eimer

Birkbeck College, London

Inhibitory processes play an important role in information processing and motor control. They are usually observed under conditions of supra-threshold stimulation. Near-threshold stimuli generally produce facilitation rather than inhibition. Recently, however, evidence for 'near-threshold inhibition' has been obtained (Eimer & Schlaghecken, 1998; Schlaghecken & Eimer, in press): Visual target stimuli were preceded by masked primes mapped to the same response as the target ('compatible'), or to the opposite response ('incompatible'). When primes were presented at fixation, responses in compatible trials were delayed, presumably reflecting an inhibition of the motor response corresponding to the prime. In contrast, with prime stimuli presented peripherally, responses were faster in compatible trials. We present evidence that this "central/peripheral asymmetry" reflects a threshold mechanism in motor control. Strong partial response activations (as elicited by foveal primes) are actively inhibited once the masking procedure removes the sensory evidence for the respective response tendency. In contrast, the weaker activations elicited by peripheral primes remain below the 'inhibition threshold,' and thus do not receive active inhibition. The finding that lowering the perceptual quality of central primes and enhancing the perceptual quality of peripheral primes reverses the central/peripheral asymmetry supports this idea.

Eimer, M. & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence. Journal of Experimental Psychology: Human Perception and Performance, 24, 1737-1747.

Schlaghecken, F. & Eimer, M. (in press). A central/peripheral asymmetry in masked priming. Perception & Psychophysics.

Selection-for-action: Evidence from bimanual reach-to-grasp movements directed toward single and multiple 'objects'

Georgina M Jackson and Stephen R Jackson

University of Nottingham

According to the integrated competition hypothesis (Duncan, Humphreys, and Ward, 1997) visual information from a single object requires less processing resources than visual information from two separate objects. Here we report four experiments which investigated this distinction in relation to planning and control of visually guided, bimanual, reach-to-grasp movements. We found that different patterns of interference were observed dependent upon whether two target objects were perceived as separate objects, or were unified, either perceptually or functionally, to form a single object. We observed that when participants executed bimanual reach-to-grasp movements toward two differently-sized cylindrical dowels (incongruent reaches) that were not connected to one another, the maximum grip apertures for each hand were significantly larger than when reaching for two unconnected dowels of the same size (congruent reaches). In contrast, when participants executed bimanual reach-to-grasp movements toward the same dowels which were now unified, either perceptually or functionally, a different pattern of effects on grip aperture were observed. In the latter case, during incongruent reaches, the maximum grip apertures of each hand became more similar (i.e. maximum grip aperture to the large target item was reduced while that to the small target item increased). These results suggest that the processing demands required by bimanual movements can vary as a function of the perceived unity of the target items.

Duncan J, Humphreys GW, and Ward R. (1997) Competitive brain activity in visual attention. Current Opinion in Neurobiology, 7, 255-261.

Understanding projectile acceleration

Marco Bertamini1 and Heiko Hecht2

1. University of Liverpool

2. Man-Vehicle Lab, MIT, Cambridge, MA, USA

Throwing and catching balls or other objects is a generally highly practiced skill for young adults, however, conceptual as well as perceptual understanding of the mechanics that underlie this skill is surprisingly poor. In 5 experiments, we investigated conceptual and perceptual understanding of simple ballistic motion. Paper-and-pencil tests revealed that up to half of all participants mistakenly believed that a ball will continue to accelerate after it has left the thrower's hand. Observers also showed a remarkable tolerance for anomalous trajectory shapes. Perceptual judgments based on graphics animations replicated these erroneous beliefs for shallow release angles. Observers' tolerance for anomalies tended to decrease with their distance from the actor.

These findings are not consistent with claims in the naïve physics literature that liken intuitive beliefs to Aristotelian or medieval physics theories. Instead, observers seem to project their intentions to the ball itself (externalization) or even feel that some power is still exerted on the ball when still close.

Implicit knowledge and motor skills: What people who can catch a ball do not know

Peter McLeod1, Nick Reed1 and Zoltan Dienes2

1. Oxford University

2. Sussex University

Ball catching, like many motor skills, is under the control of implicit knowledge. That is, people are unable to describe how they choose an appropriate speed to run at to intercept a ball before it hits the ground. People are not only unable to describe their interception strategy, they cannot describe the sensory information which controls this strategy. Given a description of this information, recognition is better than free recall. But even if the recognition judgement is made just after catching a ball, and the subjects have been primed that they will be asked to make the judgement, it is still far from perfect. The experiments described will give those members of the EPS who are in denial about the existence of implicit knowledge the grounds to make a graceful exit from this implausible state.

Session C - Friday 21 July 4-5.20 pm

The role of androgens and estrogens in the Bruce effect

Denys deCatanzaro

McMaster University

Novel males can disrupt early pregnancy in previously inseminated female mice. Castrated males lose this ability. Through ELISA procedures, we have measured levels of testosterone and 17-beta estradiol in the excretions of intact and castrated novel males while they are housed near pregnant females. Significant levels of both of these steroids are found in the urine and feces of intact males. Novel intact males become exceptionally agitated in their behaviour while near inseminated females, and actively direct their urine at these females. When 17-beta estradiol is painted directly on the nasal area of inseminated females, pregnancy reliably fails. Apart from male urine, no other chemical, including testosterone, produces such a pregnancy loss. It is established that excessive levels of 17-beta estradiol can act at the uterus and fallopian tubes to disrupt intrauterine implantation of fertilized ova. Futhermore, actions of 17-beta estradiol at the hypothalamus can interfere with pregnancy by stimulating estrus.

Effects of the benzodiazepine receptor agonist chlordiazepoxide & the 5-HT1A antagonist WAY100635 on behaviour in the rat elevated zero maze are not influenced by the light/dark cycle

Lianne Stanford1, Scott M Weiss2 and Kelly J Stanhope2

1. Department of Psychology and Neuroscience, Dalhousie University, Halifax

2. Department of Neuropharmacology, Cerebrus Ltd., Wokingham

The rat elevated zero maze is a validated model of anxiety (Shepherd et al. 1994 Psychopharm 116:56-64). In this test, rats administered anxiolytic drugs typically show a behavioural profile of increased exploratory activity (line crosses & head dips), increased time in the open areas, and less risk assessment (stretch-attends). In mice, 5-HT1A receptor antagonists have altered profiles on the elevated plus-maze when tested during different portions of the light/dark cycle (Rodgers et al., 1998 J Psychopharm 12:A32). To investigate this further, rats housed under normal or reversed light/dark cycles were tested with chlordiazepoxide (CDP), a benzodiazepine receptor agonist or with WAY100635, a 5-HT1A receptor antagonist. CDP (4 mg/kg) treated rats showed a similar anxiolytic profile in both housing groups. WAY100635 (0.01 to 0.3 mg/kg, sc: 30min) was without effect on rats from either housing group. These data show that the time of testing relative to the diurnal cycle does not alter the profiles of either CDP or WAY100635, and question the assumption that time of testing is a critical determinant of the anxiolytic properties of 5-HT1A receptor antagonists.

The effect of long-term amygdala kindling on emotional behavior may be related to receptor regulation within the dentate gyrus.

Lisa E Kalynchuk1, Janet Menard2 and Michael J Meaney2

1. Dalhousie University

2. Douglas Hospital Research Center, McGill University.

Long-term amygdala kindling in rats produces dramatic increases in emotional behavior. For example, rats subjected to 100 amygdala stimulations display extreme resistance to capture, escape behavior in an elevated plus maze, and active defensive behavior in a resident-intruder paradigm (Kalynchuk et al., 1997; Kalynchuk et al., 1999). In this paper, we present evidence that kindled rats also display heightened acoustic startle, altered patterns of open-field exploration, and significant weight gain. We also summarize the results of our recent studies investigating changes in receptor expression that may underlie the development of kindling-induced emotionality. Remarkably, most of the receptor subtypes we have investigated (i.e., 5-HT, GABA/BZ, glucocorticoid, NMDA) are changed specifically in the dentate gyrus. The dentate gyrus is an important mediator of seizure activity, contextual memory, and stress sensitivity. Because kindling-induced emotionality is triggered by exposure to novel situations, we propose that abnormal functioning within the dentate gyrus may interfere with the kindled rats' ability to cope with stress (e.g., novelty), thus leading to overly-emotional responses. (Supported by research grants from NSERC and MRC).

Session A – Saturday 22 July 9-10.40

Objects look larger with the left eye than the right eye

Chris McManus and Julia Tomlinson

University College London

Very little research has compared perception in the right and left eyes, although much has compared the right and left visual fields of the two eyes. An intriguing exception (S. Coren and C. Porac. Nature 260:257-258, 1976) suggested that objects appeared larger in the right eye of right-eyed individuals and in the left eye of left-eyed individuals. The present study tried to replicate that result using a tachistoscope which allowed presentation of images separately to right and left eyes. Each stimulus consisted of a pair of solid circles which appeared in two of four locations diagonally above or below and left or right of the fixation point. Subjects’ task was to report which circle appeared larger. The design therefore allowed eye effects to be distinguished from visual field effects. 43 subjects were tested, 19 of whom were left-eyed and 10 of whom were left-handed. Overall, circles appeared about 1.6% greater in diameter in the left eye (3.2% difference in area). There was no effect of visual field, suggesting the effects were not due to conventional cerebral lateralisation. No evidence was found for Coren and Porac’s correlation with sighting eye dominance. There were however very significant individual differences which correlated most strongly with writing hand preference (rather than throwing hand). The mechanism of these eye differences raises interesting questions for theories of lateralisation and for theories of binocular vision, where, as a part of ‘eye signature’, they may be important for disambiguating input from the two eyes.

The medial forebrain bundle must interact with the cortex for normal object recognition memory

Alex Easton (Introduced by Dr D Gaffan)

University of Oxford

In monkeys, lesions of the temporal stem, amygdala and fornix produce a severe impairment in recognition memory performance. To test the hypothesis that this impairment was due to isolating the inferior temporal cortex from the basal forebrain, we tested animals with asymmetric lesions of the medial forebrain bundle in one hemisphere (to disrupt basal forebrain activity) and of the inferior temporal cortex in the opposite hemisphere. A similar level of impairment was seen in these animals in object recognition memory as in animals with sections of the temporal stem, amygdala and fornix. This supports the hypothesis that the basal forebrain is essential for normal memory in the primate. A similar effect from asymmetric lesions of the medial forebrain bundle and the frontal cortex suggests that the basal forebrain acts as a route of subcortical communication between the frontal and inferior temporal cortices in learning.

Response reversal impairment in psychopathic individuals

R J R Blair

Institute of Cognitive Neuroscience, University College London

Psychopathy is a severe developmental disorder involving an emotional impairment, characterized by a lack of guilt and empathy, and extremely antisocial behaviour (Hare, 1991). While many of the impairments of psychopathic individuals appear to be explainable in terms of amygdala dysfunction, there is also a suggestion of dysfunction in some of the functions mediated by orbitofrontal cortex. This paper reports on the performance of psychopathic individuals on two measures of orbitofrontal cortex functioning: the ID-ED task (Dias et al., 1996) and the four pack card playing task (Bechara et al., 1997). 14 psychopaths and 14 age and IQ matched, incarcerated controls, identified using the Revised Psychopathy Checklist (Hare, 1991), were presented with the two measures. The psychopathic individuals showed striking selective deficits. On the the ID-ED task, the psychopathic individuals showed a selective deficit in response reversal but no impairment in attentional set shifting. On the four pack card playing task, the psychopathic individuals were as likely as the controls to shift from the high reward but net loss packs to the low reward but net gain packs. However, the psychopathic individuals were significantly less likely than the controls to shift their pack choice following punishment (point loss). The results are interpreted with reference to dysfunction within the connections between the amygdala and orbitofrontal cortex.

A combined neuropsychological and structural MRI study of high functioning autism

Jill Boucher1, Patty Cowell2, Paul Broks2, Neil Roberts3, Matthew Howard3 and Andrew Mayes2

1. University of Warwick

2. University of Sheffield

3. University of Liverpool

A study was carried out assessing the hypotheses that autism is associated with pathology of the medial temporal lobes (MTL) and/or the prefrontal cortex (PFC) (Robbins, 1997), using a combination of neuropsychological tests and sMRI. The sMRI investigations are described more fully in a related paper/poster.

Ten males with high functioning autism (HFA) aged 16 – 40 years, with verbal IQ’s between 86 – 150, and 10 normal controls individually matched for sex, age, and verbal IQ were tested. The HFA diagnoses were confirmed using a diagnostic checklist (Wing, 1996). The neuropsychological tests assessed executive functions (Zoo map, Brixton, Haylings, FAS), social cognition (Benton, Ekman, Eye Direction Detection, Point-Light Movement Interpretation, Face Recognition), and memory (Face and Word Recognition, Picture Recognition, Story Recall, Figure Copying and Recall), these tests being sensitive to pathology affecting the PFC, the amygdala, and hippocampal-related regions, respectively.

There were significant between group differences on the Zoo Map and Haylings; the Ekman (especially fear), Face Recognition, Eye Direction and Point Light tests. The MRI scans showed autism-specific effects in the MTL, especially the amygdala; and PFC asymmetry similar to that which occurs in other neurodevelopmental disorders. These findings support a MTL (amygdala) hypothesis, and give qualified support to a PFC hypothesis.

A selective impairment in the recognition of facial and vocal signals of disgust following brain injury.

Andrew J Calder1 , Jill Keane1 and Andy Young2

1. MRC Cognition and Brain Sciences Unit, Cambridge

2. University of York

Patient studies and brain-imaging work have shown that the recognition of facial signals of disgust may be linked to a distinct neural substrate; two areas that have been suggested are the fronto-striatal regions and the insula. (Phillips et al., 1997; Sprengelmeyer et al., 1996). Central to our interpretation of these studies is whether they have identified a brain system that is involved specifically in the perception facial signals of disgust, or one that underlies the perception disgust signals from all sensory modalities. We address this issue in a case study of NK, a 25 year old male with damage to left basal ganglia and sub-insula.

NK's ability to identify facial expressions was examined using two tests. The first contained ten examples of each of six facial expressions (happy, sad, anger, fear, disgust, and surprise) from the Ekman and Friesen (1976) series. The second included eight examples of each of seven facial expressions (the six listed above plus contempt) from the Matsumoto and Ekman (1988) set. On each test, NK showed a selective impairment in recognising facial expressions of disgust.

NK's recognition of emotion from vocal expressions was also assessed using two separate tests. The first used emotional vocalisations (e.g., laughter for happiness, retching for disgust, etc.) and contained ten examples of each of the six emotions listed above. The second comprised individual lists of five random digits, with each list spoken with intonations intended to convey particular emotional prosodies (happy, sad, anger, fear, or disgust). For both vocal tests, NK showed a significant impairment for recognising vocal signals of disgust. With the exception of a mild deficit for surprise on the first test, none of the other emotions was impaired significantly.

NK's results are consistent with damage to a brain system geared to interpret signals of disgust regardless of their modality.

Phillips, M. L., Young, A. W., Senior, C., Brammer, M., Andrew, C., Calder, A. J., Bullmore, E. T., Perrett, D. I., Rowland, D., Williams, S. C. R., Gray, J. A., & David, A. S. (1997). A specific neural substrate for perceiving facial expression of disgust. Nature, 389 (2 October), 495-498.

Sprengelmeyer, R., Young, A. W., Calder, A. J., Karnat, A., Herwig, L., Homberg, V., Perrett, D. I., & Rowland, D. (1996). Loss of disgust in Huntington's disease: Perception of faces and emotions. Brain, 119, 1647-1665.

Session B - Saturday 22 July 9-10.40

Performance as a function of number and spatial arrangement of food locations on a large radial maze

Mark R Cole

Huron College, University of Western Ontario

Cole (1999) showed that when 8, 16, 24, 32, 40 and 48 baited arms were added successively in random locations to a large radial maze, performance by rats declined only when the final set of eight arms was added. The present research was designed to assess whether this decline was primarily due to number of food locations or to configuration of food locations. In successive phases, each lasting 20 sessions, 8, 16, 24, or 48 baited arms were added to a large radial maze. Rats were tested twice daily on the maze. In one daily trial, the arms were spread out as far apart as possible, while in the other daily trial, the arms were located as tightly together as possible. Location of arms proved to be more important than number of arms when the percentage of novel entries in the first N opportunities was examined. In the Spread Condition, performance was nearly perfect with only eight arms attached, but declined as the number of arms increased to 16, 24 and 48. In the Tight Condition, performance was poor even with only eight arms attached, and declined only marginally as further arms were added. The results were interpreted as demonstrating that performance on a radial maze is more dependent upon the angular separation between adjacent arms than on the number of arms.

Symposium: "Spatial cognition in animals"

Organiser: Ron Weisman

Visual Scene Analysis in Pigeons

Marcia Spetch

University of Alberta

The world consists of a complex array of global and local visual cues that might be used to identify and remember a particular location, such as a place where food is found. Pigeons can find hidden goals using any of a variety of spatial cues, including single landmarks, arrays of landmarks, distance from an edge, and geometric shape of the environment. Pigeons' use of spatial information is remarkably general across tasks conducted on computer screens or the laboratory floor, despite drastic differences in scale of space and type response. Comparative studies have revealed interesting similarities and differences between how pigeons and other species use of spatial information.

Seasonality and spatial memory in birds

Sue Healy and Robert Biegler

University of Edinburgh

Seasonal variation in song is related to volume changes in brain regions associated with song learning. Recent evidence suggests that hippocampal volumes also vary through the year: they are large in autumn/winter and small in spring/summer. This variation appears to correlate with changes in food-storing behaviour (and thus memory for locations of stored food). We tested food-storing and non-storing tits on spatial and nonspatial memory tasks using birds caught in autumn and spring. We found seasonal differences in memory performance but, counter to prediction, in both species. It is not clear, whether there are correlated neuroanatomical changes.

Place finding in insects: Stereotypical servomechanisms

Ken Cheng

Macquarie University, Australia

Insects use a series of stereotypical place-finding servomechanisms to return to a place. Use of path integration gives way to use of landmarks close to the target location. Sun-compass and large landmarks provide directional cues. Visual flow provides an estimate of distance traveled. Landmark-based servomechanisms include beaconing: heading towards a recognized landmark, based on multiple stored views of the landmark, sensory-motor vectors: motor trajectories triggered by particular (sensory) views of a landmark, and image matching: positioning landmarks at correct retinal coordinates while facing a stereotypical direction. A 'simple-minded' sequence of servomechanisms, while not 'map-like', does the job.

Auditory Distance Perception in Black-Capped Chickadees

Leslie Phillmore, Chris Sturdy and Ron Weisman

Queen's University

In the wild, songbirds can use auditory cues to determine spatial distance to conspecifics and to identify individual conspecifics. We have been conducting perceptual experiments in the laboratory to study the auditory cues black-capped chickadees use to determine distance. Chickadees can use the amplitude of a vocalization to estimate the distance to the signal. Chickadees reared in isolation from conspecifics are not deficient in the use of auditory cues to judge distance to a vocal signal. It appears that the ability to use auditory spatial cues is not appreciably effected by experience with conspecific vocalizations at a distance.

(End of symposium)

Session C - Saturday 22 July 9-10.40

A Practical Metric for the Complexity of Graphic Displays

D C Donderi

McGill University, Montreal

A practical and effective complexity measure for character-based displays was developed by Tullis in 1983, and a comparable measure for graphical displays would be very useful. A possible measure of graphical image complexity is the change in file size after a bitmap image has been compressed. The most informationally redundant image can be compressed into the smallest file, while the least informationally redundant image can be compressed the least. Magnitude estimation scaling (MES) ratings of the subjective complexity of three different sets of 50 graphics bitmap images were made by three different groups of 10 observers each. For all three groups, the file size resulting from from JPEG image compression was highly correlated with MES judgments of subjective complexity of the original bitmap files. The relationships were r = 0.73 for a set of 50 electronic radar displays, r = 0.65 for a set of 50 electronic chart displays, and r = 0.57 for a set of 50 overlay displays containing both radar and electronic chart imagery. Work is in progress to investigate the properties of other compression algorithms.

Mechanisms for detecting texture gradients

Frederick A A Kingdom and Anthony Hayes

McGill Vision Research Unit, Montréal

Texture gradients arise in the retinal-image projection of any non-coplanar textured surface, and provide important monocular cues to surface shape. A widely held view is that texture gradients are detected by a cortical mechanism that can be approximated by a Filter-Rectify-Filter (FRF) model, where local features are picked up by Œ1st stage¹ filters (such as simple-cells) and, after conversion to energy responses via rectification (or squaring), are pooled by Œ2nd-stage¹ filters that detect variations in response energy across space. Because an FRF mechanism deals only with filter-response energy, it is sensitive to a variety of texture gradients (e.g., contrast, size, orientation), and subthreshold amounts of different texture gradients can be predicted to summate to detection threshold. We tested this prediction with stimuli that consisted of dense arrays of Gabor elements (windowed sinusoids), whose orientations, spatial frequencies, and contrasts, were modulated sinusoidally across space. Using a conventional test-threshold-versus-mask-amplitude paradigm, we found no instances of subthreshold summation between different texture gradients. We conclude that rather than using FRF mechanisms to indiscriminately detect a variety of different texture gradients, the visual system employs separate mechanisms for detecting different types of texture gradient.

Motion of drifting "isoluminant" chromatic gratings is mediated by a luminance mechanism.

Kathy T Mullen, Tatsuya Yoshizawa and Curtis L Baker.

McGill Vision Research, Department of Ophthalmology, McGill University

In previous work using random gabor kinematograms we found that there was no linear motion for red-green color vision (Yoshizawa, Mullen & Baker, Vis. Res, in press). Depending on the conditions, the motion of these isoluminant stimuli was supported either by a luminance "artifact" or by a chromatic nonlinear motion mechanism. We now ask what type of mechanism supports the motion of drifting chromatic gratings.

We measure the masking of drifting isoluminant red-green gratings (1.5cpd) by dynamic broad spectrum luminance and chromatic noise. Our results show that luminance noise masks direction discrimination thresholds of chromatic gratings but not detection thresholds over a wide range of drift rates (0.75-9Hz). On the other hand, chromatic noise masks chromatic detection thresholds, but has much less effect on direction discrimination, and at high drift rates chromatic noise has very little effect on either chromatic threshold.

The double dissociation of the effects of color and luminance noise masking suggests that the motion of drifting "isoluminant" chromatic gratings is mediated solely by a luminance mechanism.

A colour concept in male marmoset monkeys

Andrew M Derrington, Amanda Parker and Greg G Goodson

University of Nottingham

The colour vision of the male marmoset monkey (Callithrix Jacchus) is a primitive dichromatic (two-receptor) system[1]. Dichromatic colour vision may not support an innate concept of colour: it discriminates between monochromatic colours but confuses white light with monochromatic light that produces the same ratio of excitations in the two receptor types[2]. Here we show that male marmosets learn rapidly to distinguish between pairs of abstract patterns that differ only in that one member of each pair is grey-scale and the other coloured. The discrimination is not affected by manipulating the lightness of the grey-scale pattern elements and transfers to new pairs of patterns that contain only colours not included in the training patterns. We conclude that dichromatic colour vision supports an innate concept of colour and that marmosets are aware of using colour to solve perceptual problems. This may be the first demonstration that a non-human species has a concept of colour.

1. Travis, D.S., J.K. Bowmaker, and J.D. Mollon, Polymorphism of visual pigments in a callitrichid monkey. Vision Research, 1988. 28(4): p. 481-490.

2. Cornsweet, T.N., Visual Perception. 1970, San Diego: Harcourt Brace Jovanovich.

Impoverished second-order input to global linking in human vision

Robert F Hess, Tim Ledgeway and Steven Dakin

McGill Vision Research, McGill University

Department of Visual Science, University of London

Recent evidence points to the importance of global operations across spatial regions larger than individual cortical receptive fields. Studies of contour integration and motion trajectory detection suggest that network operations between local detectors underlies the encoding of extended contours in space and extended trajectories in motion. Here we ask whether such network operations also occur between second-order-detectors known to exist in visual cortex. We compared performance for stimuli composed of either first-order or second-order elements equated for visibility, and we show that unlike the first-order case, there is little or no linking interaction between local second-order detectors. This implies that the network operations thought to underlie the integration of contour information across space and direction information over space and time receive, at best, an impoverished input from local detectors that encode second-order image attributes.

Session A – Saturday 22 July 11.20-1 pm

Symposium: "Neuropsychology of human long-term spatial memory"

Organisers: R G Morris and A R Mayes

Path integration following unilateral temporal lobectomy

R G Morris1, C Worsely1, H Spiers2, C E Polkey3 and M Recce4

1. Institute of Psychiatry

2. Institute of Cognitive Neuroscience, University College London

3. Academic Neurosurgery Unit, The King's Neuroscience Centre

4. New Jersey Institute of Technology, Newark, USA.

Path integration, a component of spatial navigation, is the process used to determine position information on the basis of information about distance and direction travelled derived from self-motion cues. Following on from studies in the animal literature that seem to support the role of the hippocampal formation in path integration, this facility was investigated in humans with focal brain lesions. Thirty-three neurosurgical patients (17 left temporal lobectomy, LTL; 16 right temporal lobectomy, RTL) and sixteen controls were tested on a number of blindfolded tasks designed to investigate path integration, and on a number of additional control tasks (assessing mental rotation and left-right orientation). In a test of the ability to compute a homing vector, the subjects had to return to the start after being led along a route consisting of two distances and one turn. Patients with RTL only were impaired at estimating the turn required to return to the start. On a second task, route reproduction was tested by requiring the subjects to reproduce a route consisting of two distances and one turn; the RTL group only were also impaired at reproducing the turn but this impairment did not correlate with the homing vector deficit. There were no group differences on tasks where subjects were required to reproduce a single distance or a single turn. The results suggest that path integration is impaired patients with RTL only and suggest that the right temporal lobe plays a role in idiothetic spatial memory.

The temporal lobes, navigation and memory in large-scale virtual space

H J Spiers1, N Burgess1, E A Maguire2, S A Baxendale3, T Hartley1 and J O'Keefe1

1. Institute of Cognitive Neuroscience, University College London

2. Wellcome Department of Cognitive Neurology, Institute of Neurology, University College London

3. National Hospital for Neurology and Neurosurgery, London

Unilateral damage to the right medial temporal region is known to cause impairments on a number of spatial memory tasks, whereas bilateral damage involving both hippocampi results in substantial episodic memory deficits. In the present study we used a large-scale virtual reality town to test topographical and episodic memory in patients with unilateral medial temporal lobe damage. Sixteen left and 16 right temporal lobectomy patients were compared with 16 healthy matched control subjects. Having explored the town at length, topographical memory was then assessed by requiring subjects to navigate in, recognise scenes from and draw maps of the virtual town. Following this, subjects collected objects from two different characters in two different locations within the town. Episodic memory of these events was then assessed by a paired forced choice recognition test. Right temporal lobectomy patients were impaired on navigation, scene recognition and computer aided map drawing relative to control subjects. They were also mildly impaired on recognition of objects in the episodic memory task. The left temporal lobectomy patients were impaired relative to control subjects on their ability to remember who gave them the objects and the order in which they received the objects in the episodic memory task. Both patient groups were at chance on their ability to remember where they received the objects. These results suggest that topographical memory is largely mediated by the right medial temporal lobe, whereas some associative aspects of episodic memory are more dependent on the left medial temporal lobe.

Spatial memory and the hippocampal region: A structural MRI analysis of patients with unilateral mesial temporal lobe sclerosis

S. Abrahams1, R. G. Morris1, C. E. Polkey2 and A. Pickering3

1. Institute of Psychiatry

2. Academic Neurosurgery Unit, The King's Neuroscience Centre

3. St. George's Hospital Medical School, London,

The Nine-Box Maze, (Abrahams et al. 1997) was designed to compare spatial mapping and working memory theories of the functions of the hippocampus. The task provides separate measures of spatial, object, working and reference memory, and is analogous to the radial arm maze, encouraging the formation of allocentric rather than egocentric spatial representations. In the current investigation 47 patients with unilateral temporal lobe epilepsy (TLE) were investigated. Spatial memory deficits across both working and reference memory conditions were found in patients with a right epileptogenic focus. There was no evidence of an object working memory deficit, but a non-lateralised impairment in object reference memory was revealed. These results extend our previous findings in a larger group of patients. Moreover, the pattern of results was confirmed in a subgroup of 33 patients with unilateral atrophy localised to the mesial temporal lobe structures as revealed by volumetric analysis of magnetic resonance images. The structural analysis revealed evidence of unilateral sclerosis in the hippocampus and parahippocampal gyrus, but which did not extend into the remaining temporal cortex. In addition, spatial memory errors significantly correlated with volumetric measures of the mesial temporal lobe structures. In contrast object reference memory errors correlated with volumetric measures of the temporal cortex and not with mesial temporal lobe structures. These findings support a specialised role for the right hippocampal and parahippocampal region in spatial memory.

Spatial memory dissociations following lesions to the hippocampus and other medial temporal lobe regions

J S Holdstock1, A R Mayes2, J P Aggleton3 and N Roberts4

1. University of Liverpool

2. Department of Clinical Neurology, University of Sheffield

3. Cardiff University

4. Magnetic Resonance and Image Analysis Research Centre, University of Liverpool

The spatial memory of a patient (YR) with relatively selective bilateral hippocampal damage was investigated. Location memory was tested under conditions which encouraged the use of either an allocentric (identification of a location by its position relative to an array of external landmarks) or egocentric (identification of a location by its position relative to the observer) frame of reference. The task required subjects to remember the position of a single light presented on a board. In the allocentric condition subjects moved to a different place around the board before making a mnemonic response. In the egocentric condition stimuli were presented in darkness, which eliminated allocentric cues. YR was found to be more impaired at recalling allocentric than egocentric information after a sixty second filled interval with a tendency for the impairment to increase up to this delay. Recognition of allocentric spatial information was also impaired at the sixty second delay. More extensive medial temporal lobe damage which included the parahippocampal, perirhinal and entorhinal cortices in addition to the hippocampus (patient NM) also resulted in a deficit in allocentric but not egocentric spatial recall and this was of equivalent severity to that seen in YR. The results suggest that the human hippocampus has greater involvement in allocentric than egocentric spatial memory and that this most likely concerns the consolidation rather than initial encoding of allocentric information into long-term memory. However, a further task showed that YR's recall and recognition of the positions of specific pictures arranged on a table top was impaired even though an egocentric frame of reference could have been used. This result leads us to consider whether the allocentric spatial memory deficit reflects a more general problem of storing or retrieving certain kinds of associative information.

Right medial-temporal contributions to human episodic memory for object location and object identity in visual scenes: Evidence from functional neuroimaging

S Köhler, B. Milner and J. Crane

Montreal Neurological Institute, McGill University, Canada

Previous neuroimaging research has implicated the hippocampus and the posterior parahippocampal gyrus in encoding novel visual scenes. In the present PET study, we investigated whether these structures are also involved in recognition of spatial or object information from previously encountered scenes. Healthy participants were scanned while encoding photographs of novel scenes and while performing three different forced-choice recognition memory tests. These tests required the discrimination of familiar from altered scenes, which differed from each other either in the identity of one of the objects, the spatial configuration the objects formed, or specific object-place associations within identical configurations. Participants were also scanned in two visual baseline tasks and during encoding of individual objects presented without a scene context. Encoding of novel scenes, as compared to baseline, activated anterior portions of the hippocampus and posterior aspects of the parahippocampal gyrus bilaterally. A comparison of scene encoding with encoding of individual objects showed that the parahippocampal activation extended into a right-sided region previously described as parahippocampal place area (PPA). Recognition of scenes, as compared to baseline, activated the PPA but not the hippocampus, irrespective of whether the recognition task required retrieval of spatial or object information. Our data suggest that the anterior hippocampus is involved in forming memory representations of novel environments whereas the PPA plays a broader role in scene processing that is not limited to encoding.

(End of symposium)

Session B - Saturday 22 July 11.20-1 pm

Where is the word length effect? Right here! A reply to Bachaud-Levi et al. (1998).

Antje S Meyer1, Ardi Roelofs2, and Pim Levelt2

1. University of Birmingham

2. Max Planck Institute for Psycholinguistics, The Netherlands

The model of word production proposed by Levelt, Roelofs, and Meyer (e.g., BBS,1999) predicts that it should take speakers longer to initiate long words than shorter ones. This is because the model assumes that successive syllables of a word are generated in sequence and that speakers usually generate all syllables of a word before speech onset. In several earlier studies this prediction was borne out, but Bachoud-Levi et al. (JML, 1998) failed to obtain any evidence for a word length effect on speech onset latencies. They concluded that the model had to be modified.

In our experiments, Dutch and English speakers named objects with monosyllabic or disyllabic names, which were equally easy to recognize. When mono- and disyllabic targets were presented in mixed blocks, there was no length effect. However, when the materials were blocked for length, or when the participants were strongly encouraged to react fast, length effects were obtained. We argue that these results are consistent with our model's assumptions about the time course of phonological encoding and that processing time difference can easily be concealed (in mixed blocks and when no speed instruction is given) because of the participants' setting of a response deadline.

A critical test of the changing routes versus changing deadlines debate in print to sound translation

Ilhan Raman1, Bahman Baluch1 and Derek Besner2

1. Middlesex University

2. University of Waterloo

The word frequency effect in speeded naming of single words can be eliminated by mixing nonwords together with the words (e.g., Baluch & Besner, 1991; Hudson & Bergman, 1985) Two different accounts have been proposed. In one account, the reader shifts from relying on the addressed routine (which produces a word frequency effect) when only words are present to relying on the assembled routine (sublexical spelling-sound correspondences which do not produce a word frequency effect) when nonwords are mixed in with the words (Baluch & Besner, 1991). A different account proposes that the reader does not shift routes, but instead trys to homogenize the point in time at which an articulation is released, thus pulling the release point for high frequency words towards the release point for nonwords, consequently eliminating the word frequency effect (Lupker, Brown & Columbo, 1997).

These two different accounts are pitted against each other in a series of single-word naming experiments utilising the transparent Turkish orthography in which a robust frequency effect was previously reported (Raman, Baluch & Sneddon, 1996). The critical manipulation involves mixing words together with nonwords which are as fast as words to name, since the "changing routes" account predicts that the word frequency effect will be eliminated whereas the "changing deadlines" account predicts that a word frequency effect will be preserved. The results are inconsistent with the "changing routes" account but consistent with the "changing deadlines" account insofar as naming in a transparent script is concerned. The implications of these findings for understanding reading at the single word level in various writing systems are discussed.

Baluch, B. & Besner, D. (1991). Visual word recognition: Evidence for strategic control of lexical and nonlexical routines in oral reading. Journal of Experimental Psychology: Learning, Memory and Cognition, 17 (4), 644-652.

Hudson, P.T.W. & Bergman, M.W. (1985) Lexical knowledge in word recognition: word length in naming and lexical decision tasks. Journal of Memory and Language, 24, 46-58.

Lupker, S. J., Brown, P. & Colombo, L. (1997). Strategic control in a naming task: Changing routes or changing deadlines? Journal of Experimental Psychology: Learning, Memory and Cognition, 23 (3), 570-590.

Raman, I., Baluch, B. & Sneddon, P. (1996). What is the cognitive system's preferred route for deriving phonology from print? European Psychologist, 1 (3), 221-227.

Instantiating counter-intuitive frequency effects within a distributed memory model of naming

Thomas M Spalek. and Steve Joordens,

University of Toronto

Masson has proposed a distributed memory model as an account of the memory retrieval process underlying word recognition (1991,1995). Piercey & Joordens (1999) augmented this model with a random walk decision process in an attempt to map this general word process onto lexical decision performance. The current work examines whether a modified version of this model can also explain performance in a naming context. We will first begin by briefly summarizing some of the naming results and our modified deadline model that we presented at last year's CSBBCS meeting. Specifically, we emphasize the counter-intuitive frequency effects found when you mix monosyllabic and trisyllabic items. We then describe the results of simulations designed to instantiate our deadline assumptions within Masson's distributed framework.

Repetition blindness for words but not non-words

Jamie I D Campbell and Vanessa Hernberg

University of Saskatchewan

Repetition blindness (RB) is the failure to recognize repetition of an item in a rapid visual series of stimuli. We examined RB for English words and pronounceable non-words. Sixty undergraduates each received 192 trials. For each trial, 6-13 items (mean = 9) appeared for 86 ms sequentially in the same location. Half were randomized sequences and half formed meaningful sentences. Each sequence contained two word targets or two non-word targets separated by one to three items. Targets were brighter than the non-target words. Following the sequence, three response items appeared. For repetition trials these included the repeated target and two not-presented fillers; for non-repetition trials these included the two targets and one filler (Arnell & Jolicoeur, 1997). Participants indicated whether there were had been 0, 1 or 2 occurrences of each response item. Analysis of a-prime, percentage correct, and hits-false alarms all indicated RB for words, but no RB for non-words.

Putting automaticity in context: Reducing the Stroop effect

Colin M. MacLeod

University of Toronto at Scarborough

In a recent series of papers, Besner and Stolz have argued that "simply coloring a single letter instead of the whole word eliminated the Stroop effect." They have used this outcome to argue against the concept of universal automaticity of word reading, claiming that reading cannot be automatic if it can be prevented. I will report experiments demonstrating that the Stroop effect is not generally eliminated by this manipulation, although it is reliably decreased across both manual and vocal response modes, and relative to different types of control items. The word definitely is read in the single-letter-colored condition, but its impact on color naming is reduced. Although not diagnostic of a change in automatic reading, this reduction is an important clue to understanding the source(s) of Stroop interference.

Session C - Saturday 22 July 11.20-1 pm

An oblique effect in aesthetics: Homage to Mondrian (1872-1944)

Richard Latto, Douglas Brain and Brian Kelly

University of Liverpool

The effect of the orientation of Mondrian's paintings on their aesthetic appeal was examined. Eight paintings, four with horizontal/vertical frames in the original and four with oblique frames, were presented in eight different orientations and rated for aesthetic appeal on a 7-point scale.

There was a stronger preference for pictures presented so that their component lines were horizontal and vertical than for pictures presented with their component lines in an oblique orientation. In addition, subjects showed a preference for the original orientation, perhaps because rotation changes the lateral balance of the paintings as well as the orientation of the component lines. There was no overall preference for one frame orientation over another, but there was an interaction between frame orientation and component orientation, resulting in a preference for paintings where the components were parallel to the surrounding frame.

It is suggested that the aesthetic oblique effect reported here is related to the oblique effect in orientation perception and the privileged access which horizontal and vertical lines have to the visual system. This offers support for one possible mechanism underlying aesthetic judgements of abstract patterns: we find pleasing those stimuli which are closely tuned to the properties of the human visual system (Latto, 1995).

Latto, R. (1995). The brain of the beholder. In R. L. Gregory, J. Harris, P. Heard & D. Rose (Eds.), The Artful Eye (pp. 66-94)). Oxford, U.K.: Oxford University Press.

Five plus two equals yellow: Concept-driven photisms in digit - colour synaesthesia

Mike J Dixon, Daniel Smilek, Cera Cudahy and Philip M Merikle

University of Waterloo

When the synaesthete C views black digits, each number elicits a photism - a visual experience of a specific colour. Cytowic (1993; 1997) has claimed that photisms differ from imagery in their automaticity and their reliance on an external stimulus to elicit them. To assess the automaticity of C's photisms, digits were displayed in colours incongruent or congruent with her photism colours. Despite attempts to ignore digits, C's colour naming reaction times were significantly slower for incongruent trials than congruent trials. Finally, we triggered automatic photisms without ever physically presenting an inducing stimulus. C was shown arithmetic problems (e.g. 5 + 2) followed by a colour patch that she had to name. Naming times were significantly slower when colours were incongruent with C's photisms for the answers to problems than when colour patches were congruent. We conclude that C's photisms are automatic, but can be induced by activating the concept of digits.

Repetition priming for moving faces.

K Lander and V Bruce

University of Stirling

Recent experiments suggest that seeing a familiar face move adds additional ‘dynamic’ information for the viewer, useful in the recognition of identity (see Knight & Johnston, 1997; Lander, Bruce & Hill, 1999 in press; Lander, Christie & Bruce, 1999). This finding is consistent with the idea that familiar movement patterns – either of faces generally, or specific faces, help in their recognition. It is unclear, however, how such information may be stored in memory. One possibility is that the movement patterns are quite distinct from the static form-based representation. Alternatively, the visual representations of familiar faces may intrinsically incorporate dynamic information (cf. dynamic representations, Freyd, 1993).

Here we describe a number of experiments which aim to explore these theoretical possibilities, using a repetition priming technique. Repetition priming is the advantage demonstrated at test when a to-be-recognised item (in this case a face) is encountered earlier, at some time prior to the test event. Results suggest that a moving image primes more effectively than a static image (Experiment 1), even when the same static image is shown in the prime and test phases of the experiment (Experiment 2). This robust priming effect is not simply due to the structured sequence of images contained in a moving sequence (Experiment 3). Results are discussed within the framework of current models of face recognition.

Freyd, J.J. (1993). Five hunches about perceptual processes and dynamic representations. In Meyer, D. & Kornblum, S. (Eds), Attention and Performance, XIV: Synergies in Experimental Psychology, Artificial Intelligence and Cognitive Neuroscience - A Silver Jubilee, 99-120. Cambridge, MA: MIT Press,

Knight, B. & Johnston, A. (1997). The role of movement in face recognition. Visual Cognition, 4(3), 265-273.

Lander, K., Christie, F. & Bruce, V. (1999). The role of movement in the recognition of famous faces. Memory & Cognition, 27(6), 974-985.

Lander, K., Bruce, V. & Hill, H. (1999, in press). Evaluating the effectiveness of pixelation and blurring on masking the identity of familiar faces. Applied Cognitive Psychology.

Getting to know we learn new faces

Vicki Bruce and Zoe Henderson

University of Stirling

Recent research has highlighted the differences between the visual representations of familiar and unfamiliar faces. Unfamiliar faces are stored in an image-specific way, allowing only limited generalisation to different viewpoints, expressions or lighting conditions. Familiar face recognition, in contrast, is robust over many such variations in viewing conditions. Representations for familiar faces are weighted more towards internal features compared with unfamiliar faces. Angeli, Bruce and H. Ellis (ECVP, 1999) described preliminary results demonstrating that the shift in processing from external to internal face features can be used as an index of familiarisation as participants learn a series of individuals on video over several days, and at a recent EPS meeting, O'Donnell and Bruce described experiments suggesting that it was particularly the eyes which benefit from familiarisation. In this paper we describe the results of a new experiment where we examine the process of familiarisation when participants learn new facial identities from moving compared with multiple static images.

Individual differences in the development of face recognition: Support for a maturational change at age eight.

P A McMullen, P Dunham, and F Dunham

Dalhousie University, Halifax

Carey & Diamond (1977) suggested that before the age of 8, children recognize a face by its individual features. After this age, a whole-face (holistic) strategy has developed. Boys and girls aged 7 and 11 performed tests of Mooney faces (a test of holistic processing), Embedded figures (a test of feature-based processing) and upright and inverted face recognition. Children aged 7, successfully recognized upright faces but were at chance at the recognition of inverted faces. More importantly, upright face recognition correlated with Embedded figures performance (r= 0.56, p<0.01) and not with Mooney face performance. Children aged 11, recognized upright and inverted faces above change levels. Notably, their results showed the opposite pattern to those of the younger children. Upright face recognition now correlated with Mooney face performance (r= 0.45, p<0.05) and not with Embedded figures performance. The maturational hypothesis of face recognition was tested from an individual differences approach and supported.

Session A - Saturday 22 July 2-4 pm

Correlation, consistency, and age of acquisition effects in adult lexical processing

Andy Ellis1, Antonina Scarna1, Josephine Monaghan1 and Matt Lambon Ralph2

1. University of York

2. MRC Cognition and Brain Sciences Unit, Cambridge

Ellis and Lambon Ralph (in press) have proposed an explanation of age of acquisition effects in adult word recognition and production in terms of the behaviour of distributed memory networks trained by backpropagation. Such networks are widely used to simulate aspects of adult lexical processing. Ellis and Lambon Ralph showed that if a network is trained from the outset on one set of "early" patterns, then later patterns are added, with all of the patterns now being trained in a cumulative and interleaved fashion, then performance of the network remains superior on early compare with late patterns, even after extensive further training. This effect cannot be explained in terms of simple differences in the cumulative frequency of presentation of the patterns. Age of acquisition effects, like frequency effects, are a natural and probably inescapable property of these networks. We present new simulations which show that the age of acquisition is modulated by the similarity or correlation between early and late patterns. When they have low correlations, network structure built up during training on the early patterns is unhelpful for the assimilation of later patterns which fail to attain representations comparable to those of the early patterns. In contrast, when the correlation between early and late patterns is high, the late patterns can take advantage of the network structure established by the early patterns and age of acquisition effects are reduced. We present old and new data showing that age of acquisition effects are larger when the correlation between early and late items is low (naming objects in English and Italian; reading Japanese kanji; reading aloud exception words in English) and smaller or nonexistent when the correlation is high (reading aloud consistent words in English, and reading aloud in Italian).


Ellis, A.W., & Lambon Ralph, M.A. (in press). Age of acquisition effects in adult lexical processing reflect loss of plasticity in maturing systems: Insights from connectionist networks. Journal of Experimental Psychology: Learning, Memory & Cognition.

Homophone effects in lexical decision: An examination of a feedback account

Penny M Pexman1 and Stephen J Lupker2

1. University of Calgary

2. University of Western Ontario

Pexman, Lupker, and Jared (in review) observed the standard finding of longer response times in lexical decision tasks (LDT) to homophones (e.g., MAID/MADE) than to non-homophonic control words. Pexman et al. attributed this homophone effect to the nature of the feedback from phonology to orthography for homophones (i.e., one phonological code feeds back to two orthographic codes). In these experiments we tested three predictions of this feedback account: (a) although homophone effects are observed in LDT, regularity and homograph effects should not be, since most exception words (e.g., HAVE) and homographs (e.g., WIND) do not create the same feedback problems, (b) using pseudohomophones as the nonwords should affect only the size of the homophone effect and (c) in a phonological LDT ("does it sound like a real word?") regularity and homograph effects should be observed but homophone effects should not. The results supported our predictions for all but a subset of our (poorer) readers.

Lexical and relation-based influences on the interpretation of noun-noun phrases

Christina L Gagne

University of Western Ontario

Recent exposure to a similar combination influences the interpretation of a noun-noun phrase by increasing the availability of the phrase¹s lexical entries and (in some cases) the availability of the relation used to interpret the combination. The data show that the amount of lexical and relation priming obtained depends on whether the modifier or head noun is in common between the prime and target. The head noun prime yields more lexical priming than does the modifier prime. In contrast, relation priming is only obtained from the modifier prime. For example, oil treatment is easier to interpret when it has been preceded by a combination (e.g., oil moisturizer) using the same relation than when preceded by a combination (e.g., oil accident) using a different relation. The data are used to evaluate current theories of conceptual combination.

Phonological mediation in a semantic discrimination task: Evidence from French

Isabelle Gonthier, Alain Desrochers and Dominique Landry

University of Ottawa

Lexical phonology and semantic was investigated in word recognition. Word triplets were presented to readers who were asked to decide which of the first two words, a target word (e.g., SABLE) or a distractor, was semantically related to a test word (e.g., PLAGE). The distractor was either homophonic with a semantically related word (e.g., MÈRE which can evoke MER) or a visually similar control stimulus (e.g., MOIS). The imagery value of word triplets was manipulated. The results indicated that a) response latencies were slower when the distractor evoked a semantically related homophone than a visually similar control; b) responses to high-imagery stimuli were faster than those to low-imagery stimuli; c) no interaction was detected between the homophonic and imagery effects. These results suggest that evoked imagery does affect word meaning processing but does not constrain phonological mediation in this task.

Separating form and semantics from morphology: Evidence from cross modal masked priming.

William Marslen-Wilson and Mike Ford

MRC Cognition and Brain Sciences Unit, Cambridge

A recurring issue in the study of the English mental lexicon is to separate out evidence for morphological structure in underlying representation from the effects of form overlap (orthographic or phonological) and semantic overlap between morphologically related items (e.g., darkness/dark, rebuild/build). A partial solution to this is provided by masked priming, which can show robust morphological effects in the absence of semantic effects. However, conventional masked priming is strongly affected by orthographic overlap between primes and targets. Here we report a new masked priming paradigm, where a masked visual prime is followed not by a visual target but by an auditory target. Here there is no direct form overlap between prime and target. In two experiments we find significant identity priming (where prime and target are the same word), and significant priming between morphologically related prime/target pairs, such as adaptable/adapt. This has implications both for claims about the role of morphology in the mental lexicon, and for our understanding of the underlying mechanisms of masked priming.

The rise and fall of frequency and imageability: Noun and verb production in semantic dementia

Helen Bird1, Matthew A Lambon Ralph1, Karalyn Patterson1 and John R Hodges1,2

1. MRC Cognition and Brain Sciences Unit, Cambridge

2. University Neurology Unit, Addenbrooke's Hospital, Cambridge

This study examines the impact of progressive degeneration of conceptual knowledge on the content words used in connected speech elicited using the Cookie Theft picture description (Goodglass & Kaplan 1983). We began with an analysis of control subjects' descriptions with regard to word types and their frequency and imageability. Because the impairment of conceptual knowledge in semantic dementia is graded by concept familiarity, we created a model of a standardised normal Cookie Theft description that was then progressively degraded by the systematic removal of lower bands of word frequency. We drew two main predictions from this model: reduced availability of the lower bands of word frequency should result in (a) an apparent deficit for noun retrieval in relation to verb retrieval, and (b) an apparent reverse imageability effect. Results from a longitudinal study, in which three patients with semantic dementia each described the Cookie Theft picture on three occasions during the progression of their disease, confirmed these predictions. An additional cross-sectional analysis, adding narratives from a larger number of cases, demonstrated that the decline in ability to produce suitable words for the picture description is closely related to the extent of semantic impairment as measured in tests of word comprehension and production. Both verbs and nouns are affected by the degradation of semantic memory; the fact that the impairment to noun production is manifested earlier and more catastrophically may be attributed to the relatively lower frequency of these terms.

Goodglass, H. & Kaplan, E. (1983). The Assessment of Aphasia and Related Disorders. (2nd edition). Lea & Febiger, Philadelphia.

Session B – Saturday 22 July 2-4 pm

The name game: Using retrieval practice to learn the names of group members.

Peter E Morris1 and Catherine O Fritz2

1. Lancaster University

2. Bolton Institute

In medium sized groups such as classes it is often desirable that the members become acquainted with one another. To this end various methods of introducing group members are used with questionable degrees of success. One method of introduction, the Name Game, is based upon the principles of retrieval practice and anecdotal evidence supports its effectiveness. We compared Simple and Elaborate versions of the Name Game with a widely used method - Pairwise Introductions - and found that the Name Game participants were much better at remembering the full names of the members of their groups after 30 minutes, 2 weeks and 11 months. The effectiveness of the two Name Game methods did not differ. In a second experiment, we tested the contribution of retrieval practice by comparing the two versions of the Name Game with a procedure that matched them in number of repetitions and time spent on the task. Again, the Name Games were much superior, illustrating the benefits of retrieval practice in general and the Name Game technique in particular.

Interrupting recognition memory: Tests of the increment-to-familiarity account of the revelation effect

Marty W Niewiadomski and William E Hockley (Presenter: William E. Hockley)

Wilfrid Laurier University

The revelation effect is a puzzling phenomenon in which items on a recognition test are more likely to be judged old when they are immediately preceded by a problem solving task such as anagram solution. We evaluated Westerman and Greene's (1998) increment-to-familiarity account of this phenomenon in a series of experiments designed to examine the temporal and cumulative effects of the preceding task on the recognition probe. We found comparable revelation effects when the probe was preceded by (a) a single anagram versus two anagrams, (b) either combination of a single anagram and an arithmetic task sequence, and (c) one versus two arithmetic tasks. The results do not support the increment-to-familiarity account of the revelation effect, but are consistent with Hicks and Marsh's (1998) decision-based interpretation, in which it is assumed that the preceding task adds noise to working memory leading subjects to adopt a more liberal recognition decision criterion.

Feature frequency in recognition from short-term memory: A challenge for current theory

D J K Mewhort and E E Johns

Queen's University

Current global models of recognition memory assume a fundamental role for frequency at the feature level: The more often the constituent features of a test item have occurred during study, the easier it is to call OLD and the harder it is to call NEW. We manipulated the featural composition of artifical stimuli in a short-term recognition memory task. Performance on distractor items deteriorated with the number of constituent features studied, but, contrary to prediction, did not vary with the number of times a presented feature had occurred in the study set. Conversely, performance on targets improved when constituent features had occurred in other items within the study set. We conclude that different kinds of evidence underlie OLD and NEW responses and that recognition decisions are not correctly modelled with a signal-detection mechanism. Note that the mirror effect is not a source of difficulty for our position.

Estimating monitoring, bias and retrieval

Philip A Higham

University of Northern BC

Research is described in which a Type 2 signal detection model (SDM) is applied to data from various memory tests, yielding estimates of report bias (the tendency to offer answers to questions on a memory test or the tendency to offer information during a memory interview), monitoring (a meta-memory parameter indexed by the tendency to offer correct information and withhold incorrect information) and retrieval (the proportion of correct information on a memory test once all information is obtained). The research indicates that the estimates are affected, and sometimes dissociated, by variables (e.g., a target word’s strength-of-association to a retrieval cue) in logical and sensible ways that are consistent with current models of memory. The research also indicates that the SDM model can be applied to real-world memory problems as well, such as how best to enhance performance on aptitude tests (e.g., SAT) or on multiple-choice exams.

The role of source memory in setting the criteria for signal decision processes

C A G Hayman1, J Fugelsang2, J Cofell3 and R P Cribbie4

1. Lakehead University

2. University of Saskatchewan

3. University of Western Ontario

4. University of Manitoba

In a series of experiments testing both words and pictures as to-be-remembered material, we found that subjects recall more about the source of a memory event when they gave a "REMEMBER" rather than "KNOW" response in a prior test of recognition.  Such a finding is inconsistent with the assumption of an unidimensional vector of memory strength required in signal detection based reinterpretations (Donaldson , 1996; Hirshman & Master 1997) of dual-process views of recognition memory (Gardiner & Java, 1993; Jacoby & Dallas, 1981; Mandler, 1980).  Because increase in source memory require increases in the multidimensionality of memory, we suggest that the unidimensional vector of memory strength hypothesized in these signal detection models is at best an approximation of a multidimensional memory signal, and that criteria used in signal detection models of "REMEMBER" and "KNOW" response may be set relative to the availability of memory information for source.

Implicit/explicit memory versus analytic/nonanalytic processing: Re-thinking the mere exposure effect

Bruce W A Whittlesea and John R Price

Simon Fraser University

In studies of the mere exposure effect, rapid presentation of training items can increase liking without producing accurate recognition. The effect on liking has been explained as a misattribution of fluency caused by prior presentation. However, fluency is also a source of feelings of familiarity. It is therefore surprising that prior experience can produce liking without also causing familiarity-based recognition. We suggest that when study opportunities are minimal and test items are perceptually similar, people adopt an analytic approach, attempting to recognize distinctive features. That strategy fails because rapid presentation prevents effective encoding of such features; but it also prevents people from experiencing fluency and a consequent feeling of familiarity. We suggest that the liking-without-recognition effect results from using an effective (nonananlytic) strategy in the pleasantness task, but an ineffective (analytic) strategy in the recognition task. We suggest that explanations of the mere exposure effect based on a distinction between implicit and explicit memory are unnecessary.

Session C – Saturday 22 July 2-4 pm

Unlearned and learned behaviour of bumble bees in the absence of reward

V Simonds and C M S Plowright

University of Ottawa

This work features the development of a unique methodology to test unlearned and learned behaviour of bumble bees in the absence of reward. Two questions were asked: What attracts newly emerged bees to flowers? Does the attraction habituate over time? Two experiments were designed to test these questions. 1A: Bees made choices in a 12-arm maze between four colours and preferred yellow or blue over white or red. 1B: Choices for yellow decreased from the first to the second and third testing sessions. 2A: Bees preferred a radial pattern over a concentric pattern or a plain disc. 2B: Choice frequencies for radial decreased over the first two sessions, but increased for a novel stimulus in the third session. Results support previous findings in unlearned responses to pattern and colour, and support the previously neglected notion that bumble bees learn in the absence of reward.

The discrimination of structure

David N George and John M Pearce

Cardiff University

The solution of certain, configural, discriminations depends upon learning about the significance of combinations of stimuli, rather than of individual stimuli. According to elemental theories of conditioning (e.g., Wagner & Rescorla, 1972) mastery of a configural discrimination depends upon associations involving unique cues that are created by thecombination of two or more stimuli. Configural theories of conditioning (Pearce, 1994), on the other hand, explain the solution of these discriminations by allowing the features of a pattern of stimulation collectively to signal the outcome of a trial. The experiment to bedescribed demonstrates that pigeons can solve a complex configural discrimination which both the Wagner-Rescorla (1972) theory, and the theory of Pearce (1994), predict will be insoluble. The discrimination depends upon an appreciation of the structure of the signals for reward and nonreward. Various ways in which elemental and configural theories of conditioning might be modified to explain our results will be considered.

Pearce, J. M. (1994). Similarity and discrimination: A selective review and a connectionist model. Psychological Review, 101, 587-607.

Wagner, A. R., & Rescorla, R. A. (1972). Inhibition in Pavlovian conditioning: Application of a theory. In M. S. Halliday & R. A. Boakes (Eds.), Inhibition and Learning. San Diego, CA: Academic Press.

Losing a conditioned aversion to a taste: Extinction or counter-conditioning?

Bob Boakes and Paul Whitfield

University of Sydney, Australia

Recent findings from human evaluative conditioning and from flavour preference conditioning in rats prompted re-examination of Garcia's original claim that conditioned taste aversions are unusually resistant to extinction. Evidence against this claim has been based on giving repeated single-bottle exposure to an averted taste to thirsty rats, a procedure that typically leads to loss of the aversion. However, it also involves pairing the taste with relief of fluid deprivation and such pairing could produce counter-conditioning of the aversion. This possibility was examined by orally perfusing rats with the averted taste either just before (Thirsty condition) or just after (Sated condition) they received their daily period of access to water. Repeated exposure to the taste using this method was found to produce more rapid loss of the taste aversion in the Thirsty than in the Sated condition. The results suggest that counter-conditioning does play a role in the loss of a conditioned aversion and that, in the absence of this factor, Garcia's claim might well be correct.

The anti-emetic drug, ondansetron, interferes with lithium-induced conditioned rejection reactions, but not lithium-induced taste avoidance.

Cheryl L Limebeer and Linda A Parker

Wilfrid Laurier University

Conditioned rejection reactions displayed in the taste reactivity test are exclusively by treatments that elicit nausea.  The present experiments demonstrated that pretreatment with the anti-nausea agent, ondansetron, interfered with both the establishement and the expression of conditioned rejection reactions.  Ondansetron did not interfere with lithium-induced taste avoidance in either a one-bottle or a two-bottle test.  In fact, when rejection reactions were measured during a consumption test, ondansetron selectively attenuated rejection reactions without modifying consumption.  These results suggest that conditioned rejection reactions, but not conditioned taste avoidance, reflect nausea in rats that can be attenuated by ondansetron pretreatment.

Do squid make a visual language on their skin? The case of the Zebra display.

Jennifer A Mather

Department of Psychology & Neuroscience, University of Lethbridge

In the 1980s, Martin Moynihan suggested that the production of a combination of local components of skin pattern changes on the skin of the squid indicated an ability to form a visual language. But production of a range of components, no matter how wide or how flexible in combination, does not prove a language. The present study focuses on the variation in one display, the dark-and-pale striped Zebra. Observations of over 1200 instances of Zebra displays of Sepioteuthis sepioidea in the waters off the coast of Bonaire confirmed a huge variation in this display. Zebra could be produced on part or all of the body surface, by males or females, in different intensities and to a variety of targets. Despite the variety, the display appeared to be essentially an agonistic signal of internal state. A quantitative score of signal intensity could be calculated and was often correlated with success in intraspecific interactions. Nevertheless, the intensity was not always correlated with dominance, the signal was often directional and it was also modified to a ritualized Formal Zebra contests between adult males. This display, while of a sophistication and range of use that fulfils Moynihan's prediction of communicative sophistication, does not yet appear to suggest a visual language.

The relation between stress and the social organization of wolves and other wild canids

Peter J McLeod, Simon Gadbois and Will Moger

Acadia University, Nova Scotia

We have been relating detailed data on social behaviour of a captive wolf pack to their levels of the stress responsive hormone cortisol, assayed non-invasively from urine-contaminated snow. These data show significant differences among individuals that could be due to social rank and/or challenges to their rank. Adrenal pathology due to a tumour is a possible explanation in one case as well. Inconsistent correlations between cortisol and rank have been reported across a variety of wild canids and other social mammals. We can account for some of these differences by relating them to differences in social organization and reproductive strategies. Theoretical considerations of the degree to which species are monogamous and cooperative breeders are particularly relevant in accounting for existing data.