bluuebunny/crossref_metadata_2025 huggingface dataset:
Unity and Variety in Visual Form
Authors: Leeuwenberg Emanuel , van der Helm Peter
Published: January 2007

Some stimuli are perceived as unitary patterns, and others as dual or plural patterns. Such ‘unity-and-variety’ phenomena are explained by various process approaches of perception, such as the global precedence hypothesis, the preattentive orientation detection assumption, and the recognition-by-components model. However, these three approaches, which will be discussed in this paper, each explain a different subset of these phenomena. It will be argued that not only these three subsets but also other unity-and-variety phenomena can be explained from just one point of view by adopting the descriptive minimum principle. This principle states that the preferred interpretation of a pattern is reflected by the simplest of all possible representations of that pattern. The highest hierarchical level in the simplest pattern-representation will be called the ‘superstructure’ of the pattern. The superstructure of a pattern neither refers necessarily to the largest or global pattern component, nor is assessed nesessarily in a primary stage in the perception process. Yet, it will be argued that the superstructure is decisive in determining whether a shape is perceived either as unitary or as dual.
Illusory Depth from Moving Subjective Figures and Neon Colour Spreading
Authors: Bressan Paola , Vallortigara Giorgio
Published: January 2007

If a pattern of concentric circles, interrupted so as to produce the perception of a subjective bar extending from the centre to the periphery of the pattern, was slowly rotated in a plane perpendicular to the line of sight, observers reported seeing the bar slanted in depth and moving over complete and stationary concentric circles. When the interrupted concentric circles were completed by red segments—thereby giving rise to a neon colour-spreading effect—observers reported seeing a reddish bar, which sometimes appeared to be slanted in depth, moving behind the plane of the concentric circles. A combination of the two patterns was found to originate a compelling percept of a unitary bar slanted in depth: part of the bar (the subjective half) appeared to be located in front of its inducing elements, whereas the other part (the neon-like half) appeared to continue behind them. When translatory instead of rotary motion was used, the bars did not look slanted in depth: however, the neon bar appeared either behind or in front of the inducing lines, depending on the luminance contrast between the segments and the inducing lines themselves.
Preferential Inspection of Views of 3-D Model Heads
Authors: Harries Mark H , Perrett David I , Lavender Alan
Published: January 2007

The importance of different perspective views for the recognition of model heads was studied. In experiment 1 subjects were instructed to learn the appearance of six heads placed individually on a turntable free to rotate through 360°. Subjects did not distribute their time evenly but focussed their inspection on particular views (the full face view and a view close to the profile). Despite differential inspection of these two views during the learning phase, the face, half profile, and profile views were recognized with equal efficiency in a subsequent recognition task with static views. Experiment 2 used the inspection paradigm to investigate view preference during the recognition of heads from memory. In this experiment subjects were asked to learn the appearance of three heads each seen rotating at an even speed. In a subsequent retrieval task the subjects actively inspected six model heads on the turntable and were asked to differentiate the three heads previously seen rotating from three novel heads. The pattern of inspection in this retrieval task was equivalent to that in experiment 1. Results suggest that during the encoding into memory subjects construct descriptions of specific prototypical views of the head and that descriptions of these same views are preferentially utilised during recognition.
The Interaction of Oculomotor Cues and Stimulus Size in Stereoscopic Depth Constancy
Authors: Collett Thomas S , Schwarz Urs , Sobel Erik C
Published: January 2007

In the natural world, observers perceive an object to have a relatively fixed size and depth over a wide range of distances. Retinal image size and binocular disparity are to some extent scaled with distance to give observers a measure of size constancy. The angle of convergence of the two eyes and their accommodative states are one source of scaling information, but even at close range this must be supplemented by other cues. We have investigated how angular size and oculomotor state interact in the perception of size and depth at different distances.

Computer-generated images of planar and stereoscopically simulated 3-D surfaces covered with an irregular blobby texture were viewed on a computer monitor. The monitor rested on a movable sled running on rails within a darkened tunnel. An observer looking into the tunnel could see nothing but the simulated surface so that oculomotor signals provided the major potential cues to the distance of the image. Observers estimated the height of the surface, their distance from it, or the stereoscopically simulated depth within it over viewing distances which ranged from 45 cm to 130 cm. The angular width of the images lay between 2 deg and 10 deg.

Estimates of the magnitude of a constant simulated depth dropped with increasing viewing distance when surfaces were of constant angular size. But with surfaces of constant physical size, estimates were more nearly independent of viewing distance. At any one distance, depths appeared to be greater, the smaller the angular size of the image. With most observers, the influence of angular size on perceived depth grew with increasing viewing distance.

These findings suggest that there are two components to scaling. One is independent of angular size and related to viewing distance. The second component is related to angular size, and the weighting accorded to it grows with viewing distance. Control experiments indicate that in the tunnel, oculomotor state provides the principal cue to viewing distance. Thus, the contribution of oculomotor signals to depth scaling is gradually supplanted by other cues as viewing distance grows.

Binocular estimates of the heights and distances of planar surfaces of different sizes revealed that angular size and viewing distance interact in a similar way to determine perceived size and perceived distance.
Gravity as a Monocular Cue for Perception of Absolute Distance and/or Absolute Size
Authors: Watson John S , Banks Martin S , von Hofsten Claes , Royden Constance S
Published: January 2007

When the motion of an object is influenced by gravity (eg free fall, pendulum, wave motion), that influence may provide a cue to computing the absolute distance and/or size of the object. Formal analysis supports the claim that the distance and size of moving objects are generally computable with reference to the gravitational component of motion. Informal evidence from judgments of realism in films is consistent with this gravity-cue hypothesis.
The Role of Transparency in Perceptual Grouping and Pattern Recognition
Authors: Watanabe Takeo , Cavanagh Patrick
Published: January 2007

The shortest stimulus exposure time for which transparency can be seen was examined. In the first experiment, overlapping digits were presented for 120 ms and the luminance in the overlapping regions was varied. Subjects reported, in separate blocks of trials, either the apparent transparency of the digits or the identity of the digits. When the luminance was set so that one set of digits appeared to be seen through the other, recognition of the digits was high. When the luminance in the overlapping regions did not produce impressions of transparency, digit recognition was low. In the second experiment, digit identification at several stimulus durations was compared between stimuli that had luminance that was valid for transparency and stimuli that had invalid luminance. Performance was found to be higher in the valid luminance condition than in the invalid condition after as little as 60 ms exposure duration. This result suggests that the impression of transparency requires only relatively short exposure durations.
Learning to See Random-Dot Stereograms
Authors: O'Toole Alice J , Kersten Daniel J
Published: January 2007

In the present study some specific properties of the learning effects reported for random-dot stereograms are examined. In experiment 1 the retinal position-specific learning effect was reproduced and in a follow-up experiment it was shown that the position specificity of learning can be accounted for by selective visual attention. In experiments 2 and 3 evidence was obtained that suggests that observers can learn, to a certain degree, monocular random-dot patterns and that this learning facilitates the depth percept. This result indicates that the traditional belief that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered. In the second set of experiments the learning of two binocular surface properties of random-dot stereograms, depth edges and internal depth regions, was investigated. It was shown in experiment 4 that the depth edges of random-dot stereograms are not learned, whereas the results of experiment 5 indicate that the internal depth regions are learned. Finally, in experiment 6 it was shown that depth edges are learned when the internal depth regions of the stereogram are ambiguous. The results are discussed in terms of the importance of the particular type of stimulus used in the learning process and in terms of perceptual learning and attention.
Recognising Faces: Effects of Lighting Direction, Inversion, and Brightness Reversal
Authors: Johnston Alan , Hill Harold , Carman Nicole
Published: January 2007

When information about three-dimensional shape obtained from shading and shadows is ambiguous, the visual system favours an interpretation of surface geometry which is consistent with illumination from above. If pictures of top-lit faces are rotated the resulting stimulus is both figurally inverted and illuminated from below. In this study the question of whether the effects of figural inversion and lighting orientation on face recognition are independent or interactive is addressed. Although there was a clear inversion effect for faces illuminated from the front and above, the inversion effect was found to be reduced or eliminated for faces illuminated from below. A strong inversion effect for photographic negatives was also found but in this case the effect was not dependent on the direction of illumination. These findings are interpreted as evidence to suggest that lighting faces from below disrupts the formation of surface-based representations of facial shape.
Convergent and Divergent Perspective
Authors: Deręgowski Jan B , Parker Denis M
Published: January 2007

Use of divergent (or inverse) perspective in pictures is often regarded as arbitrary or even as erroneous in spite of the fact that entire schools of art exist in which this kind of perspective is regularly used.

An experiment is reported which shows that a significant trend towards divergent perspective is experienced by subjects viewing laterally displaced three-dimensional arrays. Centrally viewed arrays show the expected perceptual convergence. It is therefore argued that divergent perspective, under appropriate conditions, is as perceptually legitimate an experience as convergent perspective.
Sensitivity to Relative and Absolute Motion
Authors: Snowden Robert J
Published: January 2007

The threshold of sensitivity to movement could be governed by mechanisms that are sensitive either to change in spatial position, or directly to the movement itself. The use of spatially complex patterns (random-dot patterns) has been suggested to eliminate the former strategy allowing examination of the movement detecting mechanisms in isolation. By means of such a technique, thresholds for directional judgements were determined for patterns which underwent either a simple displacement or a shearing displacement. Thresholds for shearing motion were found to be around one half of those for simple motion, suggesting that relative, rather than absolute, motion governs performance for small displacements. This contrasts with previous experiments which showed that absolute motion governs performance for much larger displacements.
Spatial Orientation in Weightless Environments
Authors: Lackner James R
Published: January 2007

Illusions of body inversion and of vehicle inversion can be evoked by exposure to weightlessness in the microgravity conditions of orbital and parabolic flight. Such illusions can involve all possible combinations of self-inversion and vehicle inversion. In the absence of any patterns of external stimulation, individuals may lose all sense of body orientation to their surroundings while retaining a sense of their overall body configuration and cognitive awareness of their actual position. Touch and pressure cues provide a perceptual ‘down’ in the absence of visual input. When vision is allowed, apparent orientation is influenced by a variety of factors including the direction of gaze, the architectural layout of the vehicle, and sight of the body. The relative importance of the various factors affecting orientation changes with repeated exposure. The virtual absence of sensations of falling during exposure to free-fall emphasizes the role of cognitive factors in experienced orientation.
A Comparison of Self-Adaptation and Cross-Adaptation to Odorants Presented Singly and in Mixtures
Authors: Berglund Birgitta , Engen Trygg
Published: January 2007

Fifteen subjects made 450 judgments each by the method of magnitude estimation of dimethyl disulfide and hydrogen sulfide after prior exposure to various mixtures of them. Exposure to the same odorant clearly affected the perceived intensity of it (self-adaptation). By contrast, exposure to the other odorant showed at best a small effect (cross-adaptation). Consistent with this, adaptation to a mixture of the test odorant and another odorant is proportional to the amount of the test odorant in the mixture, and does not exceed that of self-adaptation. These results indicate that olfactory adaptation is specific and that the sense of smell is more robust than generally assumed.
Amodal Completion in Mouse Vision
Authors: Kanizsa Gaetano , Renzi Paolo , Conte Stella , Compostela Carola , Guerani Laura
Published: January 2007

The question of whether phenomena of human perception such as amodal completion are also present in visual perception in the mouse was investigated. Three experiments based on a simultaneous-discrimination task were carried out with the aid of a jumping-stand similar to the one used by Lashley. The subjects were 36 male mice (DBA/J); 12 took part in each experiment. After reaching the learning criterion (87% correct responses), the mice performed 15 test trials which were interpolated between the learning trials. The test trials were constructed so as to allow the observation of any perceptual phenomena similar to amodal perception. Of the 36 subjects, 23 reached the criterion necessary to access the test phase. A significant number of them (17 out of 23, χ2 = 5.261, p = 0.021) adopted a decisional strategy that seemed to indicate the occurrence of phenomena similar to amodal completion, and a trend in the same direction was observed in the performance of the other 6 subjects. The results allow the conclusion that a perceptual phenomenon which is similar to amodal completion in humans is present even at this phylogenetic level. Alternative interpretations are discussed.
Length Illusion in Fractional Müller-Lyer Stimuli: An Object-Perception Approach
Authors: Redding Gordon M , Hawley Erik
Published: January 2007

Length judgments were compared for Müller-Lyer stimuli and figures which had line junctions at only one end of the central shaft. A length illusion occurred for fractional figures, only slightly reduced in magnitude from the usual illusion, and the largest reduction occurred for fractional figures with fork junctions. These results are consistent with an hypothesis (drawn from artificial intelligence algorithms for interpreting line drawings) that isolated line junctions are treated as boundary junctions with constrained interpretations of convex and concave edges for the shafts of arrow and fork junctions, respectively. Information about relative position of edges may be used to constrain computation of metric properties and consequential differences in size scaling would be responsible for the illusion. Illusions can arise when information well suited for one kind of task (eg object recognition) is employed in tasks for which it is not well suited (eg size perception).
The Neural Representation of Stereoscopic Depth Contrast
Authors: Mitchison Graeme
Published: January 2007

Stereoscopic vision provides examples of contrast phenomena broadly analogous to those seen with brightness. Several authors have suggested that lateral inhibition between disparity-tuned neurons might underlie these phenomena. This type of lateral inhibition would differ from the more familiar kind which occurs with retinal ganglion cells, where an inhibitory surround has essentially a linear subtractive effect. Lateral inhibition by disparity-tuned units would introduce the nonlinearity of the tuning curve.

I argue here that the evidence nonetheless suggests that a linear subtractive mechanism operates in the stereo realm—in fact, that there is a stereo equivalent of the classical centre-surround. This seems at first sight implausible, partly because of the occurrence of the nonlinearity mentioned above, but also because disparity is only provided at certain locations in the retinal field, namely those where appropriate features are matched. I show that both objections can be easily overcome, the first because Laplacian-like centre–surrounds can be constructed from disparity-tuned cells, the second because interpolation can fill in between features, and can provide precisely the quantitative dependence upon disparities of neighbouring features which matches the experimental data.
Texture Capture in Necker Cubes
Authors: Meyer Glenn E , Howard Christine E
Published: January 2007

Texture capture can be based on illusory contours, stereopsis, outline figures, real movement, and apparent movement. Several figures are presented that demonstrate texture capture by the use of the pictorial depth cues of the Necker cube. The textures seem affixed to the sides of the cube, follow the alternations of the cube, and extend off the picture plane. A concomitant phenomenon is a subjective rarefaction of the texture in the cube. It is suggested that boundary cues determine the assignation of texture to surfaces.
The Salience of Vertical Symmetry
Authors: Wenderoth Peter
Published: January 2007

It has long been accepted that amongst patterns which are bilaterally symmetrical, those which have their axis of symmetry vertical are more saliently symmetrical than patterns whose axis of symmetry is at some other orientation. The evidence regarding the relative salience of other orientations of axis of symmetry is somewhat more equivocal. In experiment 1, subjects were required to discriminate between symmetric or random-dot patterns when the axis of symmetry was at one of eighteen different orientations, spaced 10° apart, both clockwise and counterclockwise of vertical to horizontal. The data indicated that vertical was most salient, then horizontal but that, unlike in the classical oblique effect for contrast sensitivity, performance for precisely diagonal axes was better than that for surrounding axis orientations. Additional data (from experiments 2 and 3) also showed that the salience of vertical and horizontal axes of symmetry can be manipulated extensively by varying the range of stimuli presented, presumably by manipulating the scanning or attentional strategy adopted by the observer. Many previous studies of symmetry perception may have confounded hard-wired salience for vertical symmetry with scanning or attentional strategies.
The Computation of Contour Information in Complex Objects
Authors: Boucart Muriel , Delord Sandrine , Giersch Anne
Published: January 2007

Perceptual organisation, and especially the computation of contour information, has been the object of considerable interest in the last few years. In the first part of the paper we review recent accounts on the mechanisms involved in the processing of contour. In the second part we report an experiment designed to examine (1) how physical parameters such as spatial proximity and collinearity of elements affect the integration of global contour in objects and (2) whether the activation of stored representations of objects facilitates the computation of contour. Incomplete forms varying in the spacing and the alignment of line segments on their contour were used as stimuli in a matching task. Subjects were asked to decide which of two laterally displayed figures matched a reference form presented previously. The matching target and the distractor were physically identical but differed in their orientation. In one condition the reference object was always an outline drawing of an object. In a second condition the reference object was either a complete object or a more or less identifiable incomplete form. Little variation in performance was found for forms having continuous and discontinuous contour up to a spacing of 5 pixels (10.8 min) between elements. Response times and errors increased abruptly beyond this limit. This effect occurred in the two conditions of reference stimulus, suggesting that the computation of contour information is more affected by physical constraints at early processes than by high-level processes involving activation of stored structural representations of objects.
A Selective History of the Study of Visual Motion Aftereffects
Authors: Wade Nicholas J
Published: January 2007

The visual motion aftereffect (MAE) was initially described after observation of movements in the natural environment, like those seen in rivers and waterfalls: stationary objects appeared to move briefly in the opposite direction. In the second half of the nineteenth century the MAE was displaced into the laboratory for experimental enquiry with the aid of Plateau's spiral. Such was the interest in the phenomenon that a major review of empirical and theoretical research was written in 1911. In the latter half of the present century novel stimuli (like drifting gratings, isoluminance patterns, spatial and luminance ramps, random-dot kinematograms, and first-order and second-order motions), introduced to study space and motion perception generally, have been applied to examine MAEs. Developing theories of cortical visual processing have drawn upon MAEs to provide a link between psychophysics and physiology; this has been most pronounced in the context of monocular and binocular channels in the visual system, the combination of colour and contour information, and in the cortical sites most associated with motion processing. The relatively unchanging characteristic of the study of MAEs has been the mode of measurement: duration continues to be used as an index of its strength, although measures of threshold elevation and nulling with computer-generated motions are becoming more prevalent. The MAE is a part of the armoury of motion phenomena employed to uncover the mysteries of vision. Over the last 150 years it has proved itself immensely adaptable to the shifts of fashion in visual science, and it is likely to continue in this vein.
Spatial Displacement Limits for Cyclopean (Stereoscopic) Apparent-Motion Perception
Authors: Phinney Ray , Wilson Robert , Hays Brian , Peters Kristi , Patterson Robert
Published: January 2007

The range of spatial displacements over which cyclopean (stereoscopic) apparent motion is perceived was investigated. The cyclopean stimuli were created from retinal disparity embedded in dynamic random-dot stereograms. In one experiment, the displacement range for crossed-disparity cyclopean motion was compared with that for luminance-domain motion. The results showed that cyclopean motion was perceived over spatial displacements that were about two to three times larger than the displacements over which luminance motion was perceived. In a second experiment, the displacement range for crossed-disparity cyclopean motion was compared with that for uncrossed-disparity cyclopean motion. The results revealed that the displacement range was restricted (motion quality was poor) for uncrossed motion relative to crossed motion. It is inferred that cyclopean motion from crossed disparity is represented at a coarse spatial scale, relative to luminance motion, and that cyclopean motion from uncrossed disparity is suppressed due to occlusion cues present when uncrossed stimuli are seen behind a textured background.
Difference of Spatial Frequency Selectivity between Static and Flicker Motion Aftereffects
Authors: Ashida Hiroshi , Osaka Naoyuki
Published: January 2007

The strength of motion aftereffect (MAE) was measured with the use of sinusoidal gratings of several spatial frequencies, to examine the spatial frequency selectivity of two types of MAE. With ordinary static grating as a test stimulus, to measure ‘static MAE’, the maximum aftereffect for each adapting spatial frequency was obtained at the testing stimuli of the same spatial frequency, showing spatial frequency selectivity. However, in the case when the sinusoidally flickering grating was used as a test stimulus, to measure ‘flicker MAE’, no spatial frequency selectivity was observed. The two types of MAE were considered to be based on different mechanisms. Static MAE is thought to depend on the spatiotemporal channel mechanism in the early processing stages, whereas flicker MAE might reflect higher-level processes which might occur at the extrastriate regions.
Dichoptic and Physical Information Combination: A Comparison
Authors: Uttal William R , Baruch Todd , Allen Linda
Published: January 2007

Two experiments, in which information from two different kinds of degraded (low-pass filtered and regionally averaged or blocked) visual stimuli (aircraft silhouettes) was combined, are reported. In the first experiment, the degraded images were perceptually combined by being separately presented to each eye in a dichoptic viewing situation. Both stimuli in both presentations were masked by identical random visual interference. When the two stimuli were visually fused, performance in a discrimination task was enhanced over that in control situations in which only one of the two stimuli was presented. In the second experiment the two degraded stimuli were physically superimposed prior to binocular presentation, with a similar result. The results of this hybrid (masking/binocular summation) experiment suggest that true advantageous information pooling occurs when these two types of degraded stimuli are combined either physically or dichoptically.
The Global Figural Characteristics in the Zöllner Illusion
Authors: Parlangeli Oronzo , Roncato Sergio
Published: January 2007

The Zöllner illusion has been accounted for in terms of local interactions between the vertical lines and the crossing segments. Recently, however, some evidence supporting the importance of global figural characteristics—ie of figural elements that are not directly interacting with the test lines—in the occurrence of orientation illusions has been reported. Three experiments have been conducted with parts of the Zöllner figure to test whether this illusion is affected by the global figural characteristics. The results indicate that, similarly to what has been observed for other orientation illusions, the Zöllner illusion depends on both local and global characteristics of the stimulus configuration. In addition, results suggest a similar weight for both these figural characteristics in determining the occurrence of the illusory effect. Finally, relations among different orientation illusions are also discussed.
Respective Contribution of Orientation Contrast and Illusion of Self-Tilt to the Rod-And-Frame Effect
Authors: Cian Corinne , Esquivié Dominique , Barraud Pierre Alain , Raphel Christian
Published: January 2007

The visual angle subtended by the frame seems to be an important determinant of the contribution of orientation contrast and illusion of self-tilt (ie vection) to the rod-and-frame effect. Indeed, the visuovestibular factor (which produces vection) seems to be predominant in large displays and the contrast effect in small displays. To determine how these two phenomena are combined to account for the rod-and-frame effect, independent estimates of the magnitude of each component in relation to the angular size subtended by the display were examined. Thirty-five observers were exposed to three sets of experimental situations: body-adjustment test (illusion of self-tilt only), the tilt illusion (contrast only) and the rod-and-frame test, each display subtending 7, 12, 28, and 45 deg of visual angle. Results showed that errors recorded in the three situations increased linearly with the angular size. Whatever the size of the frame, both mechanisms, contrast effect (tilt illusion) and illusory effect on self-orientation (body-adjustment test), are always present. However, rod-and-frame errors became greater at a faster rate than the other two effects as the size of the stimuli became larger. Neither one nor the other independent phenomen, nor the combined effect could fully account for the rod-and-frame effect whatever the angular size of the apparatus.
The Haptic ‘Oblique Effect’ in Children's and Adults' Perception of Orientation
Authors: Gentaz Edouard , Hatwell Yvette
Published: January 2007

The haptic perception of vertical, horizontal, and diagonal orientations was studied in children (aged 7 and 9 years) and in adults. The purpose was to test the hypothesis that the haptic oblique effect results from the different scanning movements at work when one hand explores an oblique standard and the other hand sets the response rod. In experiment 1, blindfolded subjects reproduced the orientation of a standard rod presented in either the frontal, the horizontal, or the sagittal plane, and this task was achieved either ipsilaterally (the same hand explored the standard and set the response rod) or contralaterally (one hand explored the standard and the other hand set the response rod). Since, in the sagittal plane, scanning movements are analogous when the left and right hands explore oblique orientations, no oblique effect should be observed in this condition if the hypothesis is valid. Moreover, a development effect should be observed, since young children generally rely more on movement coding than do older children and adults. Results did not support these predictions: the same oblique effect appeared in the frontal and the sagittal planes both in the ipsilateral and in the contralateral condition, and the effect of age was not in the direction predicted by the hypothesis. The results were consistent with the hypothesis in the horizontal plane only. Experiments 2 and 3 provided further tests of this hypothesis but both failed to support it. Taken together, the results of these three experiments did not support the assumption and it is suggested that the haptic oblique effect may be linked to the gravitational cues provided by the arm—hand system when it acts in the three spatial planes.
Is There a Deficit of Early Vision in Dyslexia?
Authors: Walther-Müller Peter U
Published: January 2007

A majority of dyslexic children have been found in many studies to show a deficiency of early vision, also called transient deficit. A series of four experiments was conducted to test whether or not the performance in different tasks is affected by a transient deficit. However, no clear evidence of a transient deficit was found, although the reliability of the measurements was high and the power of the statistical tests was adequate. All previous findings regarding the transient deficit can be explained by a reduced amplitude of the transient response. The same factor also accounts for a large part of the interindividual variability in this study. The failure to find a transient deficit in dyslexic children is explained only in part by language and preselection, and the outcome challenges the generality of previous findings.
A Canonical Microfunction for Learning Perceptual Invariances
Authors: Stone James V
Published: January 2007

An unsupervised method is presented which permits a set of model neurons, or a microcircuit, to learn low-level vision tasks, such as the extraction of surface depth. Each microcircuit implements a simple, generic strategy which is based on a key assumption: perceptually salient visual invariances, such as surface depth, vary smoothly over time. In the process of learning to extract smoothly varying invariances, each microcircuit maximises a microfunction. This is achieved by means of a learning rule which maximises the long-term variance of the state of a model neuron and simultaneously minimises its short-term variance. The learning rule involves a linear combination of anti-Hebbian and Hebbian weight changes, over short and long time scales, respectively. The method is demonstrated on a hyperacuity task: estimating subpixel stereo disparity from a temporal sequence of random-dot stereograms. After learning, the microcircuit generalises, without additional learning, to previously unseen image sequences. It is proposed that the approach adopted here may be used to define a canonical microfunction, which can be used to learn many perceptually salient invariances.
Production and Interpretation of Perspective Drawings by Blind and Sighted People
Authors: Heller Morton A , Calcaterra Jeffrey A , Tyler Lisa A , Burson Lynnetta L
Published: January 2007

In three experiments the production and interpretation of perspective drawings by blind and sighted subjects were examined. Blindfolded sighted, early-blind, and late-blind subjects first attempted to produce raised-line drawings of a surface at a number of angles—0° (panel horizontal), −22.5°, −45°, −67.5°, and −90° (vertical). Congenitally blind subjects did not show foreshortening in their naive raised-line drawings. However, the congenitally blind subjects were able to understand aspects of perspective, and performed as well as the blindfolded sighted and late-blind subjects in a subsequent multiple-choice task. Subjects in the multiple-choice task were required to match tangible perspective drawings to a slanted board. Although the three groups performed alike, both groups of blind subjects performed better than blindfolded sighted controls on judgments involving drawings of the vertical panel in the second experiment. In a final experiment, in which vision and touch were compared, sighted subjects were required to adjust the angle of the panel to match foreshortened, perspective drawings. This experiment yielded significantly better performance with vision than with touch, but only for drawings of the board at the vertical orientation. The results suggested that congenitally blind people may benefit from haptic exposure to raised-line configurations representing geometric perspective.
Phenomenal Competition for Poses of the Human Head
Authors: Kersten Daniel , Troje Nikolaus F , Bülthoff Heinrich H
Published: January 2007

We show a cylindrical projection of the human head. This projection is ambiguous with respect to head pose. Viewing such a projection produces perceptual competition for a few discrete views.
Parts of Visual Form: Psychophysical Aspects
Authors: Siddiqi Kaleem , Tresness Kathryn J , Kimia Benjamin B
Published: January 2007

Part-based representations allow for recognition that is robust in the presence of occlusion, movement, growth, and deletion of portions of an object, and play an important role in theories of object categorization and classification. A partitioning theory for visual form is proposed that is based on two types of parts: limb-based parts arise from a pair of negative curvature minima with evidence for ‘good continuation’ of boundaries on one side; neck-based parts arise from narrowings in shape. The motivation for this model is computational requirements for recognition. The psychophysical relevance of this model is addressed by measuring intrasubject and intersubject consistency in partitioning tasks and comparing perceived and computed parts. A series of experiments were performed in which subjects were required to partition a variety of biological and nonsense two-dimensional shapes into perceived components. Specifically, it was examined (1) whether a subject determines components consistently across different trials of the same partitioning task, (2) whether there is evidence for consistency between subjects for the same partitioning task, and (3) how the perceived parts compare with limbs and necks resulting from the computational model. The results are interpreted as suggesting that there are high levels of both intrasubject and intersubject consistency and that a large majority of the perceived parts do in fact correspond to the parts computed on the basis of our model. The implications of our model are discussed in relation to previous experimental results. Intuitive observations concerning the relationship between parts of visual form and their function are then presented. Finally, a role is envisioned for parts in figure/ground segregation; the notion of a ‘parts receptive field’ through which parts can serve as an intermediate representation between local image features, eg edges, and global object models, is suggested.
There is No Evidence That Kanizsa-Type Subjective Contours Can Be Detected in Parallel
Authors: Gurnsey Rick , Poirier Frédéric J A M , Gascon Eric
Published: January 2007

Davis and Driver presented evidence suggesting that Kanizsa-type subjective contours could be detected in a visual search task in a time that is independent of the number of nonsubjective contour distractors. A linking connection was made between these psychophysical data and the physiological data of Peterhans and von der Heydt which showed that cells in primate area V2 respond to subjective contours in the same way that they respond to luminance-defined contours. Here in three experiments it is shown that there was sufficient information in the displays used by Davis and Driver to support parallel search independently of whether subjective contours were present or not. When confounding properties of the stimuli were eliminated search became slow whether or not subjective contours were present in the display. One of the slowest search conditions involved stimuli that were virtually identical to those used in the physiological studies of Peterhans and von der Heydt to which Davis and Driver wish to link their data. It is concluded that while subjective contours may be represented in the responses of very early visual mechanisms (eg in V2) access to these representations is impaired by high-contrast contours used to induce the subjective contours and nonsubjective figure distractors. This persistent control problem continues to confound attempts to show that Kanizsa-type subjective contours can be detected in parallel.
Pictorial Depth and Framing Have Independent Effects on the Horizontal—Vertical Illusion
Authors: Williams Peter A , Enns James T
Published: January 2007

The method of constant stimuli was used to study the relative contributions of two factors (frame aspect ratio and pictorial depth) on the horizontal–vertical illusion. Four different contexts were created by combining vertically versus horizontally oriented frames with horizontally versus vertically slanted texture gradients. Points of subjective equality and just-noticeable differences were estimated from the psychophysical functions for each observer. The data revealed illusions ranging in size from 10.2% to 4.0% for the various frame–slant combinations, with no associated changes in response variability. The most important finding was that the effects of frame and depth were additive, suggesting that the illusion is determined by at least two different sets of mechanisms.
Mental-Rotation Effect: A Function of Elementary Stimulus Discriminability?
Authors: Förster Bettina , Gebhardt Ralf-Peter , Lindlar Karen , Siemann Martina , Delius Juan D
Published: January 2007

It is well known that when humans have to decide whether two differently oriented shapes are identical or mirror images their performance deteriorates as a function of the orientation disparity (mental-rotation effect). Here it is shown that the effect can also be obtained reliably with non-mirror-image, arbitrarily different polygons provided they are previously selected to be hard to discriminate. The slope of the decision speed versus orientation disparity functions was found to be inversely related to the discriminability of shapes under conditions of no, ie 0°, orientation disparity. Easily discriminable polygon pairs yielded essentially flat, no-effect functions. The arbitrary polygons that were more difficult to discriminate produced a rotation effect that was similar to those of mirror-image polygon pairs. Mirror images in this context may only be a special case of hard-to-discriminate stimuli. We also show that the speed of judging whether simple lines were of the same or different length was similarly subject to a rotation effect provided that the length differences were sufficiently small, ie when their baseline dicriminability was poor enough. It is suggested that the mental rotation of complex shapes (eg polygons) may build on rotation effects pertaining to the simpler elements of which they are composed. Further, some special effects associated with the rotation of such simpler components may explain certain peculiarities apparent in orientation invariance functions obtained with complex stimuli.
The Luminance Conditions of Transparency
Authors: Masin Sergio Cesare
Published: January 2007

In two experiments the luminance conditions for the occurrence of phenomenal transparency in achromatic flat patterns was studied. Let a, p, q and b be, respectively, the luminances of the parts A, P, Q, and B of a pattern comprising a transparent square on a two-part background, where P and Q are the parts of the square on backgrounds A and B, respectively. The results showed that | p – a|, | q – b|, and | p – q| were quantitative conditions of transparency. Metelli has proposed two ordinal conditions of transparency, | a – b| > | p – q| and p > q if a > b (or p < q if a < b). Alternatively, Masin and Fukuda have proposed the single ordinal condition p ∈ ( a, q) [or q ∈ ( p, b)]. The results showed that this second condition best predicted the occurrence of transparency.
Color Transparency
Authors: D'Zmura Michael , Colantoni Philippe , Knoblauch Kenneth , Laget Bernard
Published: January 2007

Observation suggests that the chromatic changes which elicit an impression of transparency include translations and convergences in color space. Neither rotations nor shears in color space lead to perceived transparency. Results of matching experiments show that equiluminous translations, which cannot be generated by episcotister or filter models, give rise to the perception of transparency. This implies that systematic luminance change is not needed for transparency to be perceived. These results were used for the development of a method for detecting a transparent overlay within a color image and for separating the overlay from the underlying surfaces. The method tests for the coherence of chromatic change along contours through X-junctions to help detect the contour of a transparent region. The algorithm tests locally for translation and convergence to detect a transparent region. It estimates globally the chromatic parameters of the transparent overlay in order to separate the overlay from the underlying surfaces.
Evidence for the View That Temporospatial Integration in Vision is Temporally Anisotropic
Authors: Parker Denis M , Lishman J Roly , Hughes Jim
Published: January 2007

In two experiments low-pass and high-pass spatially filtered versions of a base image were prepared and the effect of the order of delivery of sequences of filtered and base images investigated. A task that required subjects to discriminate 120 ms presentations of a full-bandwidth base image and degraded sequences that contained sets of three different spatially filtered versions, or mixtures of spatially filtered and full-bandwidth versions of the image, were used. Each set of images used in the degraded sequences was presented either so that within the 120 ms presentation window the spatial content swept from low to high spatial frequencies or from high to low. In experiment 1 twenty subjects discriminated between a base image and degraded sequences of an urban scene. Results showed both a significant overall effect of image order, with low-to-high spatial-frequency information delivery being mistaken more often for the full-bandwidth presentation than high-to-low, and that different sets of degraded image sequences varied significantly in the frequency with which they were mistaken for the full-bandwidth presentation. In experiment 2 a base and filtered versions of a human face were used in an identical task with twenty different subjects and a very similar pattern of significant results was obtained, although imposed on a lower overall error frequency than that obtained in experiment 1. It was concluded that the results of both experiments provide evidence for an anisotropic temporospatial integration mechanism in which availability of spatial information in a low-to-high spatial-frequency sequence results in more efficient integration than a high-to-low.
Guest Editorial: Colour in a Larger Perspective: The Rebirth of Gestalt Psychology
Authors: Spillmann Lothar
Published: January 2007

This overview takes the reader from the classical contrast and assimilation studies of the past to today's colour research, in a broad sense, with its renewed emphasis on the phenomenological qualities of visual perception. It shows how the shift in paradigm from local to global effects in single-unit recordings prompted a reappraisal of appearance in visual experiments, not just in colour, but in the perception of motion, texture, and depth as well. Gestalt ideas placed in the context of modern concepts are shown to inspire psychophysicists, neurophysiologists, and computational vision scientists alike. Feedforward, horizontal interactions, and feedback are discussed as potential neuronal mechanisms to account for phenomena such as uniform surfaces, filling-in, and grouping arising from processes beyond the classical receptive field. A look forward towards future developments in the field of figure–ground segregation (Gestalt formation) concludes the article.