Twenty-Sixth Annual Interdisciplinary Conference Teton Village, Jackson Hole, Wyoming January 21 -- 26, 2001 Organizer: George Sperling, University of California, Irvine ABSTRACTS =============================================================================== Benjamin T. Backus University of Pennsylvania Loss of Disparity Information During Perception of Surfaces The apparent slant of a stereoscopically defined surface can be altered by manipulating horizontal disparities, vertical disparities or felt eye position (e.g. Banks & Backus, 1998). Here we report on physically different stimuli, containing different patterns of disparity, that are perceptually indistinguishable from one another. Thus, they are true perceptual metamers (Loftus & Ruthruff, 1994). Whereas color metamerization occurs at the front end of the visual system, with the loss of spectral information during the transduction of light, stereoscopic slant metamerization occurs much later, with the loss of disparity information during combination with eye position signals. These metameric stimuli can be made distinguishable by a suitable change in eye position, as predicted by theory. ============================================================================== William Banks Pomona College Multidimensional Analysis of Memory This talk presents a method for creating a multidimensional representation of memory and using it to predict recognition memory, source memory, exclusion performance, and "false fame" effects. Despite the fact that these memory domains use different paradigms, methods of analysis, and theoretical interpretations, their results can be treated with a single analytic model. We show how to generate a multidimensional memory representation based on signal-detection theory (a version of General Recognition Theory) and make predictions for each of these paradigms. The detection model is simpler than comparable multinomial models, it is more easily generalizable, it is much easier to image and think about, and it does not make threshold assumptions. Results show clearly and intuitively the relationship between exclusion and source discrimination and how decision processes in the multidimensional space can result in effects like false fame. Several other topics, including memory representations of faces, will be addressed. ============================================================================== Charles K. Brainerd University of Arizona Representational Bases for Dual-Recognition Processes In fuzzy-trace theory's approach to dual-recognition processes, the tendency of different types of memory representations (especially, verbatim and gist traces) to provoke different types of retrieval is stressed. The theory's assumptions are implemented in the conjoint-recognition model. Results from experimental applications of this model will be reviewed. The question of whether recent findings on the model's phantom recollection parameter require the introduction of a third recognition process will be examined and possible extensions to recall will be discussed. ============================================================================== Thomas Busey Indiana University Recognition and Confidence Judgments of Faces: Contributions of Recollection and Familiarity Using blended stimuli we demonstrate a dissociation between confidence and recognition performance in experiments with naturalistic faces. Then in a series of four experiments we rule out explanations for this dissociation based on a) signal detection theory, b) unequal variance SDT, c) global familiarity (density) models, and d) sampling models. We argue that the results support a process in which both recollective and familiarity processes play a role. The results bear not only on confidence judgments of faces (important for eyewitness testimony) but also for models of face recognition that rely on a representation of the similiarity between faces as input. ============================================================================== Amy Heather Criss Indiana University Why are you confused? Item and Context Noise in Recognition Memory The purpose of the comment is two-fold. First, we point to the close similarities of BCDMEM, the model proposed by Dennis & Humphreys (in press), to extant global familiarity models of recognition memory. One of the primary differences being the order in which item and context information are used as retrieval cues. Unfortunately, there may be no plausible way to test these assumptions. Our second goal is to consider alternatives to BCDMEMs strict assumption that item noise does not contribute to recognition decisions. Item noise refers to interference from items, other than the test item, on the study list. Context noise refers to interference from incorrect contexts (e.g. from presentations of the test item prior to the study list). We argue, and demonstrate in two experiments, that both sources of noise affect recognition performance contrary to the strong position of Dennis & Humphreys (in press) in which item noise plays no role. =============================================================================== Simon Dennis University of Queensland The Syntagmatic Paradigmatic Model of Sentence Processing While connectionist models of sentence processing (e.g. Simple Recurrent Network, SRN, Elman 1993; Visitation Set Grammar model, VSG, Tabor & Tannenhaus 1999) pose a significant challenge to symbolic accounts, they also have a number of limitations. They are difficult to scale to substantive portions of a language, in terms of the size of the vocabularies they can accommodate, the length of the sentences they can process and the number of grammatical structures they capture. In addition, it has been argued that connectionist models are not able to account for the systematic nature of language use (Fodor & Pylyshyn 1988, Marcus 1999, although see Elman 1998 for counter arguments). Furthermore, it is unclear how models such as the SRN or the VSG will be able to account for the affects on reading when a sentence is immediately preceded by syntactically and relationally similar sentences. The Syntagmatic Paradigmatic (SP) model of sentence processing assumes that sentences are stored in memory as distributed traces of syntagmatic (between slot) and paradigmatic (within slot) associations. Sentence interpretation involves using the current sentence fragment as a cue to memory (employing the Minerva II model, Hintzman 1984, 1986). The retrieved vector is then treated as a set of constraints on working memory resolution of the sentence. The SP model scales well to large (> 145000 sentence) naturally occurring corpi and demonstrates strong systematicity. In addition, the working memory structures that contain the retrieved traces contain the residue of previous sentences, so that the model can account for both syntactic and relational sentence priming. ================================================================================ Tjeerd Dijkstra Ohio State University Perception of Orientation: an Empirical Bayesian Model Perception of the orientation of objects is important in our interaction with the environment. So far, research has focused on the fronto-parallel orientation of lines and gratings with the main result that vertical and horizontal orientations are perceived more accurately and precisely than oblique ones (oblique effect). We tested the orientation perception of fronto-parallel ellipses with different length-to-width (aspect) ratios in various orientations. A circle was included in the test set. Six naive subjects adjusted a broken line (probe) to match the major axis orientation of an ellipse that was placed at the center of the probe. The precision of the settings as quantified by the circular standard deviation (CSD), increased with decreasing aspect ratio. Reparametrizing aspect ratio as index of difficulty (defined as the inverse of aspect ratio minus one), CSD increased linearly with index of difficulty. This result could be captured by a simple ideal observer model were the vertices of the polygon making up the ellipse were perturbed with noise: a single noise level for each subject was sufficient to capture the results. The accuracy results show large biases, especially for the low aspect ratios (close to a circle). For the circle, subjects had a non-uniform distribution of settings. Furthermore, there are large individual differences among the subjects. We can explain these differences by a Bayesian model that takes the distribution of settings to the circle as a prior distribution. Thus the prior is obtained from the settings to a neutral stimulus. Going beyond the domain of perception of orientation, we believe empirical Bayesian modeling to be a useful new tool for vision research. ================================================================================ Barbara Dosher University of California, Irvine ?? Using Stimulus Noise to Define Attentional Processes ================================================================================ Jan Droesler Universitaet Regensburg What Warps Binocular Visual Geometry Away From the Euclidean? We all were taught in high-school that the sum of angles in a triangle is 180 deg., that the area of a circle is Pi r^2 and some other information about plane geometry. In the 19th century, however, doubts had arisen as to whether this information pertains to stringent laws. At the beginning of the 20th century, Einstein demonstrated, that the information was not valid for the physical world around us in the large. Some 50 years later Luneburg showed, that all these geometric attributes get changed in a systematic manner, as soon as our spatial vision is based on binocular visual cues alone: The sum of angles in a triangle is always smaller than 180 deg., circles have a bigger area than Pi r^2 etc. The change from monocular to binocular vision induces a change from Euclidean to non-Euclidean hyperbolic geometry. The cause for this transition has remained unknown so far. The present paper works out an answer by analyzing the data in terms of visual automorphisms. There are stimulus transformations, which leave visual structural properties invariant. Results are, that Euclidean automorphisms can be identified in the case of monocular vision, non- Euclidean hyperbolic automorphisms in the binocular case. ================================================================================ David J. Fleet Xerox PARC and Queen's University Bayesian Detection and Tracking of Motion Boundaries Visual motion at occlusions is a rich source of information about the location of surface boundaries and about the depth ordering of surfaces at these locations. Despite this, models for the processing of motion boundaries in biological systems are rare. In machine vision, these "motion boundaries" are most often viewed as a source of noise for current motion estimation techniques which assume motion is smooth. We propose a Bayesian framework for representing and estimating image motion in terms of multiple motion models, including both smooth motion and local motion discontinuity models. We compute the posterior probability distribution over models and model parameters, given the image data, using discrete samples and a particle filter for propagating beliefs through time. This talk will introduce the problem and describe our Bayesian approach, including our generative models, the likelihood computation, the particle filter, and a mixture model prior from which samples are drawn. ================================================================================ Wilson Geisler University of Texas at Austin Spatial Coding of Motion Direction in Primary Visual Cortex (tentative) When an image feature moves with sufficient speed it should become smeared across space, due to temporal integration in the visual system, effectively creating a spatial motion pattern that is oriented in the direction of the motion. Recent psychophysical evidence shows that such "motion streak signals" exist in the human visual system. Here we report neurophysiological evidence that these motion streak signals also exist in the primary visual cortex of cat and monkey. Single neuron responses were recorded for two kinds of moving stimuli: single spots presented at different velocities and drifting plaid patterns presented at different spatial and temporal frequencies. Measurements were made for motion perpendicular to the spatial orientation of the receptive field ("perpendicular motion") and for motion parallel to the spatial orientation of the receptive field ("parallel motion"). For moving spot stimuli, as the speed increases, the ratio of the responses to parallel versus perpendicular motion increases, and above some critical speed, the response to parallel motion exceeds the response to perpendicular motion. For moving plaid patterns, the average temporal tuning function is approximately the same for both parallel motion and perpendicular motion; in contrast, the spatial tuning function is quite different for parallel motion and perpendicular motion (band pass for the former and low pass for the latter). In general, the responses to spots and plaids are consistent with the conventional model of cortical neurons with one rather surprising exception: Many cortical neurons are significantly direction selective for parallel motion. We propose a simple explanation for "parallel motion direction selectivity" and discuss its implications for the motion streak hypothesis. Taken as a whole, we find that the measured response properties of cortical neurons to moving spot and plaid patterns agree with the recent psychophysics and support the hypothesis that motion streak signals are present in V1. ================================================================================ Joetta Gobell University of California, Irvine Effect of Scene Orientation on Depth Perception: Trapezoids, Windsurfers, Runways Since Ames's (1951) observation of illusory oscillation of a rotating trapezoidal figure, numerous factors that affect its depth organization have been studied. Unlike Ames's rotating trapazoids, our trapazoids merely oscillate in narrow ranges, and their perceived depth orientation is at issue. We investigate some traditional factors plus location of axis of rotation, and a global rotation of the entire scene by 90 deg (see Fig.): (a) Windsurfer configuration, (b) runway configuration. Method: The stimulus consisted of two trapezoidal figures and a central fixation point. The arrows indicate locations of possible axes of rotation. On each trial the trapezoids appeared as pictured and immediately began rotating through +/- 40 degrees. Orientation of the trapezoids (e.g. long sides to the left/right or up/down), and an axis of rotation were randomly assigned on each trial nd an axis of rotation were randomly assigned on each trial Observers reported which of the the two parallel sides appeared to be "in front". Results: Observers experience qualitatively different perceptions in (a) and (b). In Windsurfer configuration, the long parallel side is seen in front with the same probability p whether it appears on the left or the right; p depends on the observer's sensitivity to perspective versus motion cues. For runway configurations, when the long parallel side is down, it nearly always appears in front. When the long side is up, it is most often perceived in the back as part of an expanding floor. These perceptions are based on world, not retinal, coordinates. Conclusions: (1) Observers differ substantially in the weight given to linear perspective and to motion cues in determining the perceived 3D depth in ambiguous Windsurfer stimuli. (2) Runway stimuli, which differ from Windsurfers only in their global orientation, give rise to qualitatively different percepts, indicating the important involvement of high-level mechanisms in the resolution of these ambiguities. ================================================================================ David Heeger Stanford University Activity in Primary Visual Cortex Predicts Performance in a Visual Detection Task Visual attention can affect both neural activity and behavior in humans. To quantify possible links between the two, we measured activity in early visual cortex (V1, V2 and V3) during a challenging pattern detection task. Activity was dominated by a large response that was independent of the presence or absence of the stimulus pattern. The measured activity quantitatively predicted the subject's pattern detection performance: when activity was greater, the subject was more likely to correctly discern the presence or absence of the pattern. This stimulus independent activity had several characteristics of visual attention, suggesting that attentional mechanisms modulate activity in early visual cortex, and that this attention related activity strongly influences performance. ================================================================================ G.B. Henning, F. A. Wichmann, and C. M. Bird The Sensory Research Unit, Department of Experimental Psychology South Parks Road, Oxford OX1 3UD The Pedestal Effect with a Pulse Train and its Constituent Sinusoids Curves showing threshold contrast for detecting a signal grating as a function of the contrast of a masking grating of the same orientation, spatial frequency, and phase show a characteristic improvement in performance at masker contrasts near the contrast threshold of the unmasked signal. Depending on the percentage of correct responses used to define the threshold, the best performance can be as much as a factor of three better than the unmasked threshold obtained in the absence of any masking grating. The result is called the pedestal effect (sometimes, the dipper function). We used a 2AFC procedure to measure the effect with harmonically related sinusoids ranging from 2 to 16 c/deg - all with maskers of the same orientation, spatial frequency and phase - and with masker contrasts ranging from 0 to 50%. The curves for different spatial frequencies are identical if both the vertical axis (showing the threshold signal contrast) and the horizontal axis (showing the masker contrast) are scaled by the threshold contrast of the signal obtained with no masker. Further, a pulse train with a fundamental frequency of 2 c/deg produces a curve that is indistinguishable from that of a 2-c/deg sinusoid despite the fact that, at higher masker contrasts, the pulse train contains at least 8 components all of them equally detectable. The effect of adding 1-D spatial noise is also discussed. TBA ================================================================================ Rik Henson Institute of Cognitive Neuroscience & Wellcome Department of Cognitive Neurology London, England fMRI Studies of Recognition Memory Recent functional magnetic resonance imaging (fMRI) studies of recognition memory for verbal material have revealed a network of prefrontal and parietal regions associated with successful recognition. I will describe attempts to dissociate activity in these regions according to the distinction between recollective vs. nonrecollective recognition, using experimental manipulations such as the Inclusion/Exclusion procedure, Remember vs. Know judgments and confidence judgments. Though the results from these different manipulations are highly consistent, none can be said conclusively to isolate recollective processes. The relative scarcity of medial temporal activations in these studies also remains a puzzle. Nonetheless, the studies highlight the role of decision processes in yes/no recognition memory, which may have behavioural consequences that have been underemphasised by standard dual-process theories. =============================================================================== Elliot Hirshman University of Colorado, Denver Pharmacological "Lesions" =============================================================================== David E. Huber University of Colorado, Boulder Source Confusion and Discounting in Short-term Word Priming: Feature-based versus Word-based Accounts Huber et al. (in press) observed 1) a preference for or against prime-related words depending upon the manner in which prime words were processed and 2) performance deficits with priming, regardless of the direction of preference. In the probabilistic feature-based model, Responding Optimally with Unknown Sources of Evidence (ROUSE), both the preference for prime-related words as well as the priming deficits arise from source-confused feature activation. A switch to a preference against prime-related words is explained in terms of the optimal discounting of primed features. An alternative instantiation of source confusion and discounting (Ratcliff and McKoon, in press) equally accounts for these results applying the same mechanisms at the word-level. New experiments are presented providing evidence in support of the feature-based approach found in ROUSE. =============================================================================== Holly Jimison HRC and OHSU Challenges in Evaluating the Effectiveness of Web-Based Interventions for Health Care Academic time frames for evaluation are no longer acceptable (or of interest) in providing feedback on rapidly developing technologies. However, there are many biases associated with information collected from convenient and naturally occurring experiments in the use of web-based systems. I will discuss the various techniques that are being used to measure the effectiveness of web-based approaches to delivering health care information and decision assistance to patients. The current challenges include * a rapidly changing background environment of competing web sites and growing use of the Internet by consumers, * interventions that are modified and improved frequently over the course of the trial, and * a need for rapid feedback. I will also describe a decision-focused framework for evaluation that makes use of early feedback on system use. =============================================================================== Steve Joordens University of Toronto at Scarborough TBA =============================================================================== Leonid Kontsevich Smith-Kettlewell Eye Research Institute How Random Are We? I will describe a novel approach for finding regularities in time sequences. This approach has minimum assumptions regarding the regularities to be found and efficiently uses limited number of examples for finding solution. Applied to random binary sequences generated by humans it predicts about 80% of decisions. This algorithm may resemble an associative mechanism for human memory. =============================================================================== Kenneth J. Malmberg Indian University How Study Time Affects Implicit and Explicit Memory: The "One-Shot" Hypothesis Direct, explicit, memory performance (e.g. recognition and recall) is improved by both spaced and massed study of an item. However, indirect, implicit, memory performance (e.g. word fragment completion and perceptual identification) is improved only by spaced study. Within the framework of the 'Retrieving Effectively from Memory Theory' (REM), these results are predicted when a new assumption, called the one-shot hypothesis, is incorporated: Increasing the number of massed repetitions or the time of massed study increases the item-content information stored, but (beyond some minimum time or number) does not increase the amount of context information stored. Experiments using source memory and free recall procedures verify this one-shot hypothesis, and suggest that context is fully encoded within approximately two seconds. =============================================================================== Georg Meyer Keele University What Holds Speech Together? - Perceptual Organization by Formant Structure We are remarkably good at understanding speech in background noise. A possible explanation for this is that we organise our auditory environment into multiple streams that we can selectively attend to. Experimental data suggests that simple features, such as the fundamental frequency or the spectro-temporal structure of sounds, can be used to segregate competing sounds into separate streams. The segregation process only requires low-level knowledge of the structure of sound, such as that all harmonics in an auditory scene that share the same fundamental frequency are likely to be produced by a single source. The ideas underlying auditory scene analysis and an application of this segregation strategy to speech recognition in noise will be discussed in the first part of the talk. A fundamental problem of auditory scene analysis, when applied to speech sounds, is the inherent contrastive nature of speech, which means that successive speech segments of a single speaker are designed to maximally different. A 'good auditory speech analyser' should separate a single speech stream into many different fragments. We know that this is not the case because we perceive speech as a single stream. I will use the second part of the talk to describe some experiments that suggest that formant structure one of the cues used to 'hold speech together.' ================================================================================ Jeff Mulligan NASA Ames Research Center Scan-path Analysis of Air Traffic Control Displays Air traffic displays are dense with information, but it is not known exactly which pieces of information are accessed at what times. Better understanding of how these displays are used, leading to a model of the human operator, will help display designers to create more effective and efficient displays. To this end, we investigated visual search performance using simulated air traffic displays. Subjects viewed displays containing 16 or 20 aircraft including a "conflict pair," a pair of aircraft on a collision course. Subjects were asked to locate and identify the conflict pair. All aircraft were at one of four fixed altitudes. Two methods for representing altitude were investigated: 1) a numeric string in a small block of text known as the "data tag" (similar to current air traffic displays); 2) use of a different color to represent the craft at each of the four altitudes. Eye fixation scan-paths were monitored using a head-mounted video camera system, a digital video recording system, and image analysis software. Statistics of empirical scan-path data were compared with those of synthetic scan-paths generated by a computer model. The computer model reproduced basic data features by the manipulation of parameters such as memory decay and the size of the region about fixation within which aircraft headings can be perceived. We found marked differences in the scan-path data between conditions with and without color-coding. Without color-coding, we saw large numbers of very small saccades, produced when the subject read information in a data tag. The small saccades were, for the most part, absent when color coding was used; instead, we saw a larger proportion of relatively large saccades. In a more detailed analysis, we classified each saccade on the basis of the initial and final fixated objects. For each fixation, the nearest display object was identified and its type (aircraft icon or data tag, altitude, etc.) was noted. Each saccade was then placed into a category, such as craft-to-own-tag, craft-to-same-altitude-craft, etc. When color coding was employed, subjects tended to scan the aircraft within an altitude group, resulting in a greater proportion of saccades between objects at the same altitude, and a larger average saccade size. Subjects used color coding to efficiently locate and identify aircraft on a collision course. We hope to generalize the model to allow prediction of performance with operational air traffic displays. =============================================================================== Kevin Murnane University of Maryland Contextual Information as a Retrieval Cue =============================================================================== Ken Norman University of Colorado, Boulder Modeling Hippocampal and Neocortical Contributions to Recognition Memory Dual-process models posit that recognition judgments are based on recall of specific details, and on feelings of familiarity (that index, holistically, how well the test probe matches stored memory traces). One way to place dual-process models on stronger footing is to look at how the brain implements recall and familiarity; in recent years, a very clear story has emerged whereby recall depends on the hippocampus, and familiarity-based recognition is supported by the medial temporal neocortical regions that surround the hippocampus. To explore how these structures contribute to recognition, we have constructed neural network models that incorporate key anatomical and physiological properties of the hippocampus and neocortex, respectively -- these models provide a principled way of predicting how manipulations will affect recall and familiarity. One prediction is that a list strength effect should be present for hippocampally-driven recall, but not for neocortically-driven familiarity; I will explain why the models make this prediction, and I will present new empirical results consistent with this prediction. More generally, I hope to demonstrate that mathematical models of recognition can benefit by tapping into our growing knowledge of how the brain gives rise to recognition memory. =============================================================================== Tatiana Pasternak University of Rochester Direction of Motion Is Remembered in Retinotopic Coordinates We asked if the processing of visual motion information in a visual working memory task is retinotopicaly organized. Monkeys compared the directions of two moving random-dot stimuli, sample and test, separated by a temporal delay, and reported whether the stimuli moved in the same or in different directions. By presenting the two comparison stimuli in separate locations in the visual field, we determined whether the storage and retrieval/comparison components of the task were carried out in retinotopic coordinates. Two psychophysical measures of direction discrimination provided nearly identical estimates of the critical spatial separation between sample and test stimuli that lead to a loss in threshold. Direction range thresholds measured with dot stimuli consisting of a range of local directional vectors, were affected by spatial separation when a random-motion mask was introduced during the delay into the location of the upcoming test. The selective masking at the test location suggests that the information about the remembered direction was localized and available at that location. Direction difference thresholds, measured with coherently moving random dots, were also affected by separation between the two comparison stimuli. The separation at which performance was affected in both tasks increased with retinal eccentricity in parallel with the increase in receptive field size in neurons in cortical area MT. The loss with transfer of visual information between different spatial locations suggests a contribution of cortical areas with localized receptive fields to the performance of the memory task. The similarity in the spatial scale of the storage mechanism derived psychophysically and the receptive field size of neurons in area MT suggest that MT neurons are central to this task. ================================================================================ Misha Pavel Oregon Granduate Institute Fusion-Based Robust Signal Processing by Humans and Machines In my presentation, I will briefly note the wide range of benefits that can be derived from biological and machine data fusion, but I will then focus on fusion in service of pattern recognition. Although many existing automatic pattern recognition systems have achieved considerable success over the past fifty years, most of them lack robustness - the ability to perform as well as possible in unpredictable and changing environments. In contrast, biological systems seem to be much more resilient to the environmental changes that are, at least partially, irrelevant to the tasks. The fact that current artificial systems lack the robustness found in natural systems leads to questions that address the basic differences between the natural and the statistically optimal approaches. Our preliminary analysis of these differences led us to hypothesize new methodology for pattern recognition. I will briefly describe a working hypothesis whereby data fusion in conjunction with neural-like computation can be used to achieve more robust pattern recognition performance that that obtained with more traditional approaches. I will illustrate the approach on one or two specific and realistic examples. ================================================================================ Zygmunt Pizlo Purdue University Status of the Zone Theory of Color Coding The so called zone theory incorporates the trichromatic theory and the opponent process theory. The trichromatic and opponent process theories make contradictory predictions, which poses a logical problem for the zone theory. These three theories will be discussed in the context of experiments by Helmholtz (1852), Maxwell (1856), Hecht (1928) and Hurvich & Jameson (1951). ================================================================================ Roger Ratcliff, Mark Segraves, and Anil Cherian Northwestern University Neural Recordings and Simple Two-choice Decisions We report data from a simple two-choice task using rhesus monkeys as subjects. The behavioral results are presented as accuracy rates and reaction time distributions for correct and error responses. We recorded from buildup/prelude cells in the superior colliculus during the task. The diffusion model was fit to the behavioral data and the estimates of decision time from the model were shown to match the estimates from the neural recordings. We also found evidence for competition between the two responses in neural activity: when response A was highly likely and the monkey made response B, there was increased activity in the cells corresponding to response A (though activity in the cells corresponding to B was higher). We discuss the current state of modeling two-choice tasks in the neurobiological domain. =============================================================================== RECOGNITION MEMORY SESSION - Abstract The dominant model of recognition memory has been a single-process continuous-state model that assumes that memory access consists of the interaction of retrieval cue and a memory structure (Anderson, 1973; Gillund & Shiffrin, 1984; Murdock, 1982). The result of memory access is a level familiarity associated with a test item, and this serves as the sole source of information on which to base the recognition decision. While dominant in the field, few researchers believe that recognition is always based only on the familiarity of the test item (cf. Gillund & Shiffrin, 1984). It is strongly suspected, at least at times, that the retrieval of information from memory also contributes to recognition. That is, a dual-process model of recognition is tacitly accepted that incorporates both a familiarity-based and a retrieval- based process (e.g. Atkinson & Juola, 1973; Gillund & Shiffrin, 1984; Yonelinas, 1997). The problems for the field have been to identify empirical phenomena that require retrieval-based memory access in order to be explained and how to measure the contributions of the different memory access processes. The purpose of the proposed AIC session is to explore theories of recognition memory, measurement issues, and empirical evidence that bears on the dual-process issue. ================================================================================ Tim Rickard University of California, San Diego Memory Retrieval Practice: Strengthening or Instance Accrual? A commonly held view in the field is that most learning in long-term memory involves independent instance, or exemplar, accrual. Logan (1988) extended this view to account even for RT improvement with practice on specific items. However, this extreme case appears to constitute the ideal conditions for prototype learning, or strengthening, if in fact such a process occurs in nature. To explore this issue, RT distributions fits were evaluated for simplest case instance and strengthening models of memory retrieval practice. Two methodological features were: 1) separate distribution fits to the practice data for each item, and 2) de-convolution of the perceptual-motor component of the RT distribution based on independent data. The results suggest a fundamental weakness in the instance distribution model, as well as a somewhat surprising shape in the de-convolved retrieval distribution. Overall, the results favor a strengthening account, raising the question of what principle(s) determines whether practice yields strengthening or instance accrual in a given task domain. =============================================================================== Caren Rotello University of Massachusetts ROC Analyses of Recognition Memory and Remember-Know The Remember/Know paradigm has been used extensively to distinguish between two subjective states of awareness in recognition: explicit recollection (remembering) of the event, and more general familiarity (knowing) that suggests the event occurred. Recently, a single-process familiarity-based model of the data from that paradign has been presented. That model makes predictions about the nature of the receiver-operating characteristic (ROC) curve, which I will discuss and evaluate. Dual-process and multidimensional models of the Rembmber/Know data will also be considered. ================================================================================ Michael D. Rugg Institute of Cognitive Neuroscience & Wellcome Department of Cognitive Neurology London, England Fractionation of Recognition Memory: Convergent Evidence? I will briefly review electrophysiological (ERP) studies relevant to the question whether recognition memory is supported by two (or more) underlying processes, and then present some new ERP data that both supports and qualifies previous findings. I will also make some general remarks, in light of the other contributions to the session, on the extent to which different approaches to the questions of whether and how recognition memory should be modelled as multiple processes converge on a common answer. =============================================================================== Steven K. Shevell University of Chicago Spatial Localization of a Virtual Object A remarkable property of human vision is the ability to discriminate the spatial positions of objects. For example, two abutting vertical lines are seen to be offset horizontally when their positions differ by just 5 sec of arc (less than 1/4 inch offset across the length of a football field). Several theoretical accounts have been offered for spatial localization, including an ideal-observer model (Geisler, 1984), an aggregation of retinal-location 'signs' (e.g. the centroid model of Hess & Holliday, 1996), and a contrast-sensitive spatial-filter model (Wilson, 1986). These models were considered by studying spatial localization of a perceived object-from-motion: a sphere rotating around the vertical axis. Measurements using the perceived sphere, which resulted from successively presented frames of dots, were compared to results with a stationary pattern of dots (one frame from the sphere) or with randomly moving dots, which differed from the sphere only with respect to the correlation between dots' locations in successive frames. The measurements, which showed the classical drop of positional acuity with contrast, demonstrated best spatial localization for the perceived sphere (object-from-motion). This cannot be explained by models that depend on only independent retinal information in each frame, including ideal observer and centroid models. A neural representation of inferred shape or contour is consistent with the results (cf. McKee, 1991). =============================================================================== Richard Shiffrin Indiana University Paradoxes of Backwards Induction Abstract: I explore the normative bases for reasoning, in the domain of backward induction as analyzed in two person alternate play games. In the 'centipede' game of 20 trials, the two players alternate turns, each trying to maximize gain (not to beat the opponent). A player can end the game, or continue. A decision to continue loses that player $1 (to the bank) and gives the opponent $10. Forward reasoning suggests extended play, as each player accumulates much money by so doing. Backward reasoning suggests stopping on trial one, because it is always certain the next player will stop (consider trial 20, on which the player will stop to prevent a sure loss of $1). I propose a resolution to this paradox that some researchers find strange. ================================================================================ Philip L. Smith University of Melbourne Attentional Dynamics of Masked Detection The role of spatial attention in the processing of elementary stimulus attributes has, until recently, been somewhat unclear. One group of studies supports the view that simple stimulus attributes are detected preattentively and that focal attention is involved only in higher-order processing, such as that subserving the identification of complex forms. A second group of studies supports the view that detection sensitivity is enhanced for stimuli presented at attended locations. Data reported by Smith (2000) suggest that the variable which determines whether or not a signal enhancement effect is obtained is whether or not backwardly-masked stimulus presentation is used. In this talk I review new and existing evidence for the masking hypothesis. I then present a model of stimulus processing in cued detection, the attention-gated stochastic integrator, which predicts the different attentional effects obtained with masked and unmasked presentation. This model, which combines the multichannel leaky stochastic integrator model of Smith (1995) and the episodic theory of attention of Sperling and Weichselgartner (1995), assumes that the rate of information accrual in a sequential-sampling decision mechanism is gated by selective attention. Differential predictions for masked and unmasked presentation follow from the assumption of greater informational persistence for unmasked stimuli. =============================================================================== George Sperling University of California, Irvine TBA ================================================================================ Mark Steyvers Stanford University Small World Networks and Semantic Networks Watts and Strogatz (1998) showed that many real life networks such as the electric power grids, social networks, and the neural network of the worm Caenorhabditis Elegans are small-world networks. These networks exhibit small average distance between nodes as well as strong local clustering. We show that several types of semantic networks, e.g. associative networks and networks formed by linking words with the contexts they appear in are all small world networks. We will show how to make use of the small average distances in semantic networks to place words in a low dimensional space. The distances between words in this space can predict confusions in recognition memory and recall. ================================================================================ Bosco S. Tjan University of Southern California Object Recognition by Anarchy Most conventional theories of object recognition assume that within a single visual-processing pathway only one form of representation is derived and used to recognize objects. Versatility of the visual system comes from having multiple visual-processing pathways, each supporting a particular class of objects or recognition tasks. We propose and simulate a theoretically simpler alternative, capable of explaining the same set of data and more. A single primary visual-processing pathway, loosely modular, is assumed. Memory modules are attached to sites along this pathway. Object-identity decision is made independently at each site. A site's response time is a monotonic-decreasing function of its confidence regarding its decision. The system's response is the first-arriving response from any site. The effective representation of such a system, determined behaviorally, appears to be self-adapting and specialized for different tasks and stimuli. This is merely a reflection of the decisions being made at the appropriate level of abstraction. =============================================================================== Sophie Wuerger Keele University The Intrinsic Blur of the Visual System for Luminance and Chromatic Stimuli The responsiveness of the human visual system to an image depends on a multitude of image features, such as the wavelength (colour) of the visual stimulus and its spatial content. Three main factors limit the spatio-chromatic sensitivity of the visual system: the optics of the eye, retinal sampling, and post-receptoral neuronal factors. We investigated a specific aspect of the spatio-chromatic sensitivity of the human visual system, namely how much blur the visual system can tolerate in different colour directions and its dependence on contrast. Using the model proposed by Watt & Morgan (1983 Vis. Res., 23, 1457-1477) we estimated the internal blur for each colour direction and arrived at the following estimates: 1 minute of visual angle for red-green and luminance, and 1.8 minutes of visual angle for yellow-blue. Furthermore, the contrast dependence of blur sensitivity is identical for red-green and luminance. We conclude that for (stationary) stimuli the blur tolerance in the luminance and the red-green channel is predicted by the absolute cone contrast and is independent of the sign of the L and M cone contrast. (luminance: L and M cone contrast of same sign; red-green: L and M cone contrast of opposite sign). Our results are consistent with the hypothesis that stationary luminance and red-green stimuli are encoded by the same mechanism. Blur tolerance is not predicted by the known contrast sensitivity function for luminance, red-green, and yellow-blue gratings. Our measurements of the chromatic blur tolerance of the human visual system are potentially useful for image processing when when lowpass filters are used for noise removal. =============================================================================== Joongnam Yang University of Chicago Illuminant estimation in surface color perception When we view an object, it is easy to judge the color of its surfaces, even though the color signal arriving at the eye has two components: surface spectral reflectance and spectral illumination. The visual system somehow disentangles the two so that the appearance of the object is nearly constant under changes of illumination. This requires that the visual system somehow discount the illuminant, which can be achieved with knowledge about the illuminant. The scene contains information about the illuminant in what are called illuminant cues, which include shadows, specular reflections, and mutual inter-reflections. One of the cues, specular reflection, was investigated to determine the role of this cue in color perception of a scene with 3-D objects and flat surfaces. Two different methods, cue perturbation and cue elimination, were used. In the cue perturbation method, all cues in the scene were consistent with one illuminant except the cue in question, which was consistent with a different illuminant. The results showed that the specularity cue, when perturbed, affected color perception, but only when the cue was perturbed from Illuminant A to D65, not in the other direction. In the cue elimination method, the specularity cue was entirely removed from the scene. Surface color perception was affected when the cue was eliminated. Together these results indicate that specular reflection is an important cue that affects surface color perception. ============================================================================== Last update: 18jan00