Search

Provides information on the Annual General Meeting of the Applied Vision Association which was held in Bristol, England on March 31, 2004. Changes in the association; Topics discussed during the meeting; Papers presented during the conference.

Despite their limitations, linear filter models continue to be used to simulate the receptive field properties of cortical simple cells. For theoreticians interested in large scale models of visual cortex, a family of self-similar filters represents a convenient way in which to characterise simple cells in one basic model. This paper reviews research on the suitability of such models, and goes on to advance biologically motivated reasons for adopting a particular group of models in preference to all others. In particular, the paper describes why the Gabor model, so often used in network simulations, should be dropped in favour of a Cauchy model, both on the grounds of frequency response and mutual filter orthogonality. [ABSTRACT FROM AUTHOR]

One of the major difficulties in graph classification is the lack of mathematical structure in the space of graphs. The use of kernel machines allows us to overcome this fundamental limitation in an elegant manner by addressing the pattern recognition problem in an implicitly existing feature vector space instead of the original space of graphs. In this paper we propose three novel error-tolerant graph kernels — a diffusion kernel, a convolution kernel, and a random walk kernel. The kernels are closely related to one of the most flexible graph matching methods, graph edit distance. Consequently, our kernels are applicable to virtually any kind of graph. They also show a high degree of robustness against various types of distortion. In an experimental evaluation involving the classification of line drawings, images, diatoms, fingerprints, and molecules, we demonstrate the superior performance of the proposed kernels in conjunction with support vector machines over a standard nearest-neighbor reference method and several other graph kernels including a standard random walk kernel. [ABSTRACT FROM AUTHOR]

Recent discussion regarding whether the noise that limits 2AFC discrimination performance is fixed or variable has focused either on describing experimental methods that presumably dissociate the effects of response mean and variance or on reanalyzing a published data set with the aim of determining how to solve the question through goodness-of-fit statistics. This paper illustrates that the question cannot be solved by fitting models to data and assessing goodness-of-fit because data on detection and discrimination performance can be indistinguishably fitted by models that assume either type of noise when each is coupled with a convenient form for the transducer function. Thus, success or failure at fitting a transducer model merely illustrates the capability (or lack thereof) of some particular combination of transducer function and variance function to account for the data, but it cannot disclose the nature of the noise. We also comment on some of the issues that have been raised in recent exchange on the topic, namely, the existence of additional constraints for the models, the presence of asymmetric asymptotes, the likelihood of history-dependent noise, and the potential of certain experimental methods to dissociate the effects of response mean and variance. [ABSTRACT FROM AUTHOR]

DOVES, a database of visual eye movements, is a set of eye movements collected from 29 human observers as they viewed 101 natural calibrated images. Recorded using a high-precision dual-Purkinje eye tracker, the database consists of around 30 000 fixation points, and is believed to be the first large-scale database of eye movements to be made available to the vision research community. The database, along with MATLAB functions for its use, may be downloaded freely from http://live.ece.utexas.edu/research/doves, and used without restriction for educational and research purposes, providing that this paper is cited in any published work. This paper documents the acquisition procedure, summarises common eye movement statistics, and highlights numerous research topics for which DOVES may be used. [ABSTRACT FROM AUTHOR]

This paper calls attention to research showing that binocular disparity, which is an effective cue to depth, plays a secondary role, at best, in the perception of 3D shape. This claim has implications both for how shape should be studied and how this unique perceptual property should be modeled. These issues are discussed from a historical perspective, which shows how the failure to appreciate the importance of the Gestalt grouping principle called 'Figure–Ground Organization' led to many unfruitful efforts. It also calls attention to how this situation can be remedied. [ABSTRACT FROM AUTHOR]

When presented against a highly lit black background, dimly illuminated white paper strips appear white even when they are equiluminant with the background. Such an example of simultaneous lightness constancy cannot be accounted for by receptor gain control because of the equiluminance. Moreover, this demonstration shows that lightness cannot be reduced to 'relative brightness' as is widely believed. [ABSTRACT FROM AUTHOR]

This paper follows from studies by Joung, van der Zwan and Latimer (2000) in which symmetrical dot patterns with one axis of symmetry were used to produce tilt aftereffects (TAEs). The present paper investigates TAE functions produced by symmetrical dot patterns with multiple axes of symmetry. In Experiments 1 and 2, TAE functions produced by dot patterns with two axes of symmetry were compared with TAE functions produced by line stimuli arranged in the same orientation and location as the axes of symmetry in the dot patterns. Similar functions were found. In Experiments 3 and 4, functions produced by dot patterns with four axes of symmetry were compared with functions produced by line stimuli arranged in the same orientation and location as the four axes of symmetry. Again, similar functions were found. These experiments demonstrate that line stimuli and dot stimuli produce similar TAE functions. The implications of these results are discussed. [ABSTRACT FROM AUTHOR]

In this paper we discuss image understanding and object recognition as a class of processes which involve binding what is seen with what is known. It follows from this perspective that it is important to explicate how systems may learn about spatial information from images, how it is encoded, and, how, in turn, such knowledge is matched with new image data. As well as discussing very specific solutions to these problems, this paper questions the view that our scientific understanding of image understanding is sufficiently circumscribed by the study of how image features are extracted and matched, per se. [ABSTRACT FROM AUTHOR]

The article features Terry Caelli, former director of Australia's National Information and Communications Technology (NICTA) Research Laboratory of Canberra, Australian Capital Territory. Caelli completed his undergraduate and doctor of philosophy degrees in Mathematics and Mathematical Psychology at the University of Newcastle, Australia. He also served as a lecturer and senior lecturer at the Universities of Melbourne and Newcastle from 1974 to 1982. He has made a number of contributions in various fields like human and artificial vision and robotics.

Tackles several issues concerning achromatic vision in humans, including vernier acuity and peripheral vision.

In this paper we define the content of information in an image and show how it can be computed by taking into account different levels of resolution, in the framework of information theory and the thermodynamics of irreversible transformations. The results thus obtained will eventually be exploited to derive a mechanism for active exploration of visual space suitable to perform a dynamic coupling between the agent and its environment. [ABSTRACT FROM AUTHOR]

Because of the great heterogeneity of subjects and styles, esthetic perception delineates a special and elusive field of research in vision, which represents an interesting challenge for cognitive science tools. With specific regard to the role of visual complexity, in this paper we present an experiment aimed to measure this dimension in a heterogeneous set of paintings. We compared perceived time complexity measures — based on a temporal estimation paradigm — with physical and statistical properties of the paintings, obtaining a strong correlation between psychological and computational results. [ABSTRACT FROM AUTHOR]

This paper is a call for greater use of individual differences in the basic science of visual perception. Individual differences yield insights into visual perception's functional organization, underlying biological/environmental mechanisms, and utility. I first explain the general approach advocated and where it comes from. Second, I describe five principles central to learning about the nature of visual perception through individual differences. Third, I elaborate on the use of individual differences to gain insights into the three areas mentioned above (function, biology/environment, utility), in each case describing the approach advocated, presenting model examples from the literature, and laying out illustrative research proposals for the case of stereopsis. [ABSTRACT FROM AUTHOR]

Representational art tries to capture a 3D world on a 2D surface, and artists often discuss this in relation to the projected image on window panes and mirrors. But are 2D projections on transparent surfaces useful to learn about projections in general? Most people are unaware of the 2D projected size of objects on the surface of mirrors. They also incorrectly expect that these projections always get smaller with distance of the target object from the mirror, and do not change with distance of the observer (when the target is stationary). In this paper we extend this result about surfaces of mirrors to surfaces of windows, and we confirm that the errors that people make are not specific to Western culture by replicating the study in China. In contrast to their errors about projections, people are more accurate at predicting how field of view will vary depending on distance of the observer from a mirror or window. To explain how this pattern of (false) beliefs can stem from experience we argue that people do not perceive projections on transparent surfaces. [ABSTRACT FROM AUTHOR]

This paper describes three examples of illusion installation in a science museum environment from the author's collaboration with the artist and architect. The installations amplify the illusory effects, such as vection (visually-induced sensation of self motion) and motion-induced blindness, to emphasize that perception is not just to obtain structure and features of objects, but rather to grasp the dynamic relationship between the self and the world. Scaling up the size and utilizing the live human body turned out to be keys for installations with higher emotional impact. [ABSTRACT FROM AUTHOR]

Rules of composition in paintings form a rich probe into the principles of perceptual processing that have been discussed for centuries. These principles can be studied by controlled scientific experiments, but an alternative approach is to use the art works themselves as a database for direct analysis. This paper focuses on the analysis of composition in relation to the canvas frame. An underlying principle is the compositional pyramid rising from the bottom of the frame to a center of consciousness high on the midline, which also finds its expression in the configuration of portrait paintings. The analyses presented reveal a dominant positioning principle for one eye in a portrait to lie on the vertical axis with an unbiased accuracy of the order of ±5%. Analysis of the vertical location shows that the dominant height is at or above the Golden Section level on the vertical axis. In general, the layout of the portrait follows the principle of the compositional pyramid, with a center of consciousness at its apex, but there are many other compositional principles at work in the corpus of portraits in general. Analysis of the portraits of particular artists reveals that special features of their work must be considered in order to identify those that do and do not conform to the eye-centering principle. [ABSTRACT FROM AUTHOR]

The derivation of a reliable, subjective measure of awareness that is not contaminated by observers' response bias is a problem that has long occupied researchers. Kunimoto et al. (2001) proposed a measure of awareness (a′) which apparently meets this criterion: a′ is derived from confidence ratings and is based on the intuition that confidence should reflect awareness. The aim of this paper is to explore the validity of this measure. Some calculations suggested that, contrary to Kunimoto et al.'s intention, a′ can vary as a result of changes in response bias affecting the relative proportions of high- and low-confidence responses. This was not evident in the results of Kunimoto et al.'s original experiments because their method may have artificially 'clamped' observers' response bias close to zero. A predicted consequence of allowing response bias to vary freely is that it can result in a′ varying from negative, through zero, to positive values, for a given value of discriminability (d′). We tested whether such variations are likely to occur in practice by employing Kunimoto et al.'s paradigm with various modifications, notably the removal of constraints upon the proportions of low- and high-confidence responses, in a visual discrimination task. As predicted, a′ varied with response bias in all participants. Similar results were found when a′ was calculated from pre-existing data obtained from a patient with blindsight: a′ varied through a range of positive results without approaching zero, which is inconsistent with his well-documented lack of awareness. A second experiment showed how response bias could be manipulated to yield elevated values of a′. On the basis of these findings we conclude that Kunimoto's measure is not as impervious to response bias as was originally assumed. [ABSTRACT FROM AUTHOR]

Beck (1972) pointed out that grouping tasks, where one set of elements is distinguished from another, do not imply associative links within either set of elements but could rely on processes of segregation. Although many physiological theories of grouping are purely associative there are not many methods of isolating associative processes psychophysically. One method has been to measure common resolutions of elements when they are presented under conditions of depth and motion ambiguity. In the present paper a number of the issues surrounding grouping are considered, particularly in relation to associative processes. These include whether grouping is post-constancy and post-completion, grouping with and without emergent features, the role of top-down processing and attention and the explanatory role of general principles such as simplicity and likelihood. [ABSTRACT FROM AUTHOR]

The ability to locate an object in the visual field is a collaboration of at least three intermingled processes: scanning multiple locations, recognizing the object sought (the target), and ending the search in cases when the target is not found. In this paper, we focus on the termination rule. Using distribution analyses, it is possible to assess the probability of termination conditional on the number of locations examined. The results show that on some trials without target, the participants carried out more comparisons than there are objects in the display; in other conditions, they carried out fewer comparisons than objects. Because there were very few errors, the premature stops were not pure guesses. We present models to account for these findings. The distributions of terminations help determine the slopes of the functions relating response time to set size. [ABSTRACT FROM AUTHOR]

In backward visual masking, it is common to find that the mask has its biggest effect when it follows the target by several tens of milliseconds. Research in the 1960s and 1970s suggested that masking effects were best characterized by the stimulus onset asynchrony (SOA) between the target and mask. In particular, one claim has been that the SOA for which masking is optimal remains fixed, even as target and mask durations varied. Experimental evidence supported this claim, and it was accepted as an SOA law. However, recent modeling (Francis, 1997) and experimental studies (Macknik and Livingstone, 1998) argued for new ISI (interstimulus interval) and STA (stimulus termination asynchrony) laws, respectively. This paper reports a mathematical analysis and experimental tests of the laws, The mathematical analysis demonstrates unsuspected relationships between the laws. The experiments test the predictions of the SOA, ISL and STA laws. The data favor the ISI law over the SOA and the STA laws. [ABSTRACT FROM AUTHOR]

This paper is concerned with the information used in open-loop pointing to visually perceived targets. Stereoscopic stimuli were used to produce illusory relative egocentric distances, which were inconsistent with the angles of vergence required to fuse the targets. One of the stimuli was a rectangle slanted around a vertical axis. Four participants in Experiment I reported its slant and pointed to its edges. The slant was hugely underestimated (condition A) unless the rectangle was flanked by other surfaces (condition B). The relative depth of a pair of dots placed in front of the rectangle was also misperceived due to depth-contrast effect. The critical finding is that pointing responses were not based on vergence but were consistent with depth estimates, both for the rectangle and for the dots. Experiment 2 revealed the conditions necessary for pointing to be consistent with perceived relative position. The different target distances were either randomised allowing inter-trial comparisons, or presented only one per session to prevent them. Pointing was similar to estimates only in the randomised condition showing the significance of inter-trial comparisons. It is proposed that participants used the remembered motor command and kinesthetic sensations of a previous movement as a reference, attempting to make the difference between successive movements the same as a visually perceived depth difference between successive targets. [ABSTRACT FROM AUTHOR]

The present paper provides an analysis of the pointing errors of a patient with unilateral optic ataxia (O.K.) following right hemispheric damage, revealing the type of errors related to the use of the contralesional hand and/or to the reaching of targets located in the contralesional visual field, In addition, comparison between immediate and delayed pantomime pointing allow testing of whether pointing deficits of this patient are specific to real-time visuo-motor control and, subsequently, whether delay could improve his pointing performance. The results show different patterns in the four hand-field combinations. The following conclusion can be drawn from the results of the delayed condition. In the case of patient O. K., the delay reduced the pointing variability for both hands in the left visual field but not in the right visual field. However, the pointing biases did not improve accordingly. As in healthy subjects, target locations tended to be coded in memory with a bias directed toward the fixation point. These results are discussed and contrasted with respect to those previously obtained in the literature in patients with bilateral optic ataxia. [ABSTRACT FROM AUTHOR]

This paper reports a comparison between two tasks of visual search. Two observers carried out, in separate blocks, a saccade-to-target task and a manual-target-detection task. The displays, which were identical for the two tasks, consisted of a ring of eight equally spaced Gabor patches. The target could be defined by a difference from the distractors along four possible dimensions: orientation, spatial frequency, contrast or size. These four dimensions were used as variables in separate experiments. In each experiment, performance was measured over an extensive range of values of the particular dimension. Thresholds were thus obtained for the saccade and the manual response tasks. The nature of the response was found to modify the relative visual sensitivity. For orientation differences, manual response performance was better than saccade-to-target performance. The reverse was true for spatial frequency and contrast differences, where saccade-to-target performance was better than manual response performance. We conclude that saccade-selection in a search task draws on different visual information from that used for manual responding in the equivalent task. The two tasks thus differ in more than the different response systems used: the results suggest the action of different underlying neural visual mechanisms as well as different neural motor mechanisms. [ABSTRACT FROM AUTHOR]

Whether contrast adaptation may enhance contrast discrimination is a question that has remained largely unresolved because of conflicting empirical evidence. Greenlee and Heitger (1988), for example, reported that contrast discrimination may be enhanced after contrast adaptation, while Maattanen and Koenderink (1991) did not. This paper aimed to account for the different conclusions reached by these independent researchers by manipulations of key differences that exist between the two studies. It is shown that contrast discrimination may be enhanced after adaptation, but that these effects can vary markedly across subjects and test conditions. Enhancements in contrast discrimination are reported to be significant when adapting and testing at low levels of contrast, but just significant at higher levels of contrast. For high contrast signals, enhancements are shown to be independent of temporal frequency but dependent upon viewing conditions. Under binocular viewing conditions, enhancements in contrast discrimination thresholds are shown to be significantly higher than under monocular viewing conditions. It is suggested that the different conclusions reached by Greenlee and Heitger and by Maattanen and Koenderink may be explained by their respective differences in viewing conditions. The former study used binocular, while the latter study used monocular viewing with an occluding eyepatch. [ABSTRACT FROM AUTHOR]

Because the estimation of thresholds is daily practice in sensory psychophysics, efficient methods must be used to reduce experimental cost and burden. A large number of such methods are available, and each one further has a multitude of variants. All methods presumably provide a threshold estimate that is the stimulus level at which repeated testing would result in a specific percentage of correct responses on a forced-choice task, a percentage that varies across methods and variants thereof. A recent study (García-Pérez, 1998) showed that the most popular method (up-down staircases with fixed step sizes) yields threshold estimates that do not correspond to the presumed percent-correct points. Two modifications of this type of staircase have recently been proposed. In one (Zwislocki and Relkin, 2001), the up-down rule does not require correct responses to occur consecutively. In the other (Kaernbach, 1999), subjects are allowed to respond 'don't know' instead of guessing at random when unsure. Although the statistical basis of either modification were described in general, only a few of their many variants were subjected to evaluation under a limited set of conditions. This paper provides an extensive evaluation of a reasonable number of variants of either modification under a broad set of conditions. The results show that they are generally unfit for threshold estimation because in most cases the percent-correct point that is targeted varies greatly with the relative size of the steps with respect to the spread of the psychometric function. Dependable conditions for the use of these modified staircases are also determined. [ABSTRACT FROM AUTHOR]

Relative binocular disparity cannot tell us the absolute 3D shape of an object, nor the 3D trajectory of its motion, unless the visual system has independent access to how far away the object is at any moment. Indeed, as the viewing distance is changed, the same disparate retinal motions will correspond to very different real 3D trajectories. In this paper we were interested in whether binocular 3D motion detection is affected by viewing distance. A visual search task was used, in which the observer is asked to detect a target dot, moving in 3D, amidst 3D stationary distractor dots. We found that distance does not affect detection performance. Motion-in-depth is consistently harder to detect than the equivalent lateral motion, for all viewing distances. For a constant retinal motion with both lateral and motion-in-depth components, detection performance is constant despite variations in viewing distance that produce large changes in the direction of the 3D trajectory. We conclude that binocular 3D motion detection relies on retinal, not absolute, visual signals. [ABSTRACT FROM AUTHOR]

Forced-choice staircases with fixed step sizes are used in a variety of formats whose relative merits have never been studied. This paper presents a comparative study aimed at determining their optimal format. Factors included in the study were the up/down rule, the length (number of reversals), and the size of the steps. The study also addressed the issue of whether a protocol involving three staircases running for N reversals each (with a subsequent average of the estimates provided by each individual staircase) has better statistical properties than an alternative protocol involving a single staircase running for 3N reversals. In all cases the size of a step up was different from that of a step down, in the appropriate ratio determined by García-Pérez (Vision Research, 1998, 38, 1861-1881). The results of a simulation study indicate that a) there are no conditions in which the 1-down/1-up rule is advisable; b) different combinations of up/down rule and number of reversals appear equivalent in terms of precision and cost; c) using a single long staircase with 3N reversals is more efficient than running three staircases with N reversals each; d) to avoid bias and attain sufficient accuracy, threshold estimates should be based on at least 30 reversals; and e) to avoid excessive cost and imprecision, the size of the step up should be between 2/3 and 3/3 the (known or presumed) spread of the psychometric function. An empirical study with human subjects confirmed the major characteristics revealed by the simulations. [ABSTRACT FROM AUTHOR]

The problem of learning is arguably at the very core of the problem of intelligence, both biological and artificial. In this paper we sketch some of our work over the last ten years in the area of supervised learning, focusing on three interlinked directions of research: theory, engineering applications (that is, making intelligent software) and neuroscience (that is, understanding the brain's mechanisms of learning). [ABSTRACT FROM AUTHOR]

This paper introduces a new approach to assess visual representations underlying the recognition of objects. Human performance is modeled by CLARET, a machine learning and matching system, based on inductive logic programming and graph matching principles. The model is applied to data of a learning experiment addressing the role of prior experience in the ontogenesis of mental object representations. Prior experience was varied in terms of sensory modality, i.e. visual versus haptic versus visuohaptic. The analysis revealed distinct differences between the representational formats used by subjects with haptic versus those with no prior object experience. These differences suggest that prior haptic exploration stimulates the evolution of object representations which are characterized by an increased differentiation between attribute values and a pronounced structural encoding. [ABSTRACT FROM AUTHOR]

This paper is organised approximately into two halves. In the first half, I review evidence about the structure of the visual system, and I use that evidence to frame what I think are widely held but often implicit ideas about how it works, namely that vision is principally analysis of retinal input. These ideas have been strongly influenced by engineering approaches; form a default view of the visual system that suffuses all the language used to describe it (at least in visual neuroscience); and are to some extent supported by the structural evidence. In the second half, I explore some inconvenient facts from neuroanatomy and neurophysiology which are quite uncomfortable for the traditional view. I then set out a contrary view of how structure and function are linked in the visual system, which is a neurobiological variety of the quite developed view in psychophysics that vision is better understood as knowledge-rich inference. Finally, I explore some of the ramifications of this view for neurophysiological understanding of how the visual system might operate during normal vision. [ABSTRACT FROM AUTHOR]

As opposed to dealing with the geometry of objects in the 3D world, this paper considers the geometry of the visual input itself, i.e. the geometry of the spatio-temporal hypersurface defined by image intensity as a function of two spatial coordinates and time. The results show how the Riemann curvature tensor of this hypersurface represents speed and direction of motion, and thereby allows to predict global motion percepts and properties of MT neurons. It is argued that important aspects of early and middle level visual coding may be understood as resulting from basic geometric processing of the spatio-temporal visual input. Finally, applications show that the approach can improve the computation of motion. [ABSTRACT FROM AUTHOR]

Most current models of human and animal vision assume that the processes of vision involve 2D (or even 3D) internal representations of the external world - an iconic representation. Within these models, recognition involves some form of lineal, areal or volumetric comparison of these internal representations (either learned or innate) with current sensory inputs. However, this view has recently come under criticism. In this paper, a neural model of vision is explored in which this iconic world view is replaced by a temporally ordered trace of (essentially) local features. The model employs hierarchical, recurrently linked, self-organizing topological maps. [ABSTRACT FROM AUTHOR]

Introduces the September 2001 issue of 'Spatial Vision' journal which explored the application of basis functions to the understanding of visual processing in humans and animals.

Offers views on visual adaptation. Need to understand the properties of the underlying mechanisms of sensory adaptation.

The article discusses several papers published within the issue including one about binocular visual field and another regarding stereopsis.

The editorial focuses on articles appearing in the issue discussing new variations and applications of signal detection theory. The articles discussed address the issues of perceiving without awareness, recognition of objects at a distance, and how stimulus features are combined in making visual judgments. This issue represents a small sample of exciting theoretical developments and novel applications of signal detection theory in visual perception.

In theory, properties of clutter can be defined globally or locally. However, in the literature, the distinction between local and global clutter is arbitrary, where the standard approach of setting the local domain to twice the expected target size, in applying local clutter metrics, is adopted without any justification. This paper addresses this problem and considers the implications for the application of clutter metrics. It was found that the size of the local clutter region around a target has a strong effect on the probability of detection of that target and that this is affected by regions much larger than twice the target size. It was also discovered that this effect was much stronger for targets subtending less than 0.8 degrees of visual angle than for larger targets. In the case of the former, the fall-off in human visual performance with clutter region size was approximately quadratic, compared to a slight linear fall-off for larger targets. A simple model is presented explaining these phenomena, indicating that the auto-covariance function characterising the clutter is the main determinant of the size of the region of local clutter. [ABSTRACT FROM AUTHOR]

Editorial. Introduces a series of articles on visual perception and understanding images, published in the November 2000 issue of `Spatial Vision.'

Many of the phenomena of object classification can be derived from a representation specifying a nonaccidental characterization of an object's parts (geons) and relations, termed a geon structural description (GSD). Such a representation: (a) enables the facile recognition of depth-rotated objects, even when they are novel, (b)provides the information that is employed not only to distinguish basic-level but also highly similar members of subordinate-level classes, and (c) enables mapping onto verbal and object-reasoning structures. Recent psychophysical and neural investigations of object recognition have provided additional support to this theory of object representation. [ABSTRACT FROM AUTHOR]

Proposes an alternative account that explains persistence as a side-effect of excitatory feedback in neural circuits for contour extraction. Scales in the boundary contour system; Simulation results; Discussion of the results.

Editorial. Provides information on the annual meeting of the Applied Vision Association in London, England on March 17, 1999 which focused on visual search topics.

Presents an obituary for Bela Julesz, who served on the Editorial Advisory Board of the journal "Spatial Vision."