bluuebunny/crossref_metadata_2025 huggingface dataset:
Binocular Rivalry and Fusion under Scotopic Luminances
Authors: O'Shea Robert P , Blake Randolph , Wolfe Jeremy M
Published: January 2007

A study is reported of human binocular rivalry and fusion over a range of luminances from scotopic to photopic. At scotopic light levels, rivalry alternations were very slow and complete. Suppression spread over much larger areas of the visual field than at photopic light levels. As luminances decreased from photopic to scotopic levels there was a rod—cone break for binocular rivalry. Mean suppression durations became abruptly greater as light levels dropped below those allowing the cones to be active. Horizontal disparities allowing fusion were 4 to 6 times greater at scotopic than at photopic light levels. Binocular vision at scotopic luminances was sluggish and of low resolution. It is as though connections to, and within, binocular vision are changed when light levels allow only rod input.
Experiments on the Afterimages of Stimulus Change (Dvořák 1870): A Translation with Commentary
Authors: Broerse Jack , Dodwell Peter C , Ehrenstein Walter H
Published: January 2007

In 1870 Dvořák rejected Helmholtz's eye-movement account of motion aftereffects (MAEs) on the grounds that it was inconsistent with previous reports of nonuniform rotation in MAEs induced with Plateau spirals. Subsequent observations with spirals that were modified to induce both expanding and contracting MAEs simultaneously, together with the use of stationary negative afterimages during induction and test, were offered as further counter-examples to the eye-movement hypothesis. Dvořák's conjectures that perception (and misperception) of movement involves a unitary perceptual dimension of stimulus change also led him to investigate whether aftereffects comparable to MAEs could be induced along other stimulus dimensions in vision (luminance gradients), and in audition (gradients of pitch and intensity). It is suggested that Dvořák's observations, taken as a whole, may be interpreted as an attempt to provide evidence challenging the Helmholtzian traditions underpinning eye-movement accounts of MAEs. The nature and outcomes of these observations are provided in a translation of the original work, and are subsequently discussed in relation to some contemporary empirical counterparts.
Apparent Depth with Motion Aftereffect and Head Movement
Authors: Ono Hiroshi , Ujike Hiroyasu
Published: January 2007

Coupling a motion aftereffect (MAE) produced by horizontal shearing motion with a lateral head movement yields apparent depth. In experiments 1 and 2, respectively, the magnitude and the decay time of this apparent depth were measured. In experiment 3, it was found that the stimulus that produced an MAE in experiments 1 and 2 failed to do so when it was viewed while the head moved leftward and rightward and depth was seen.
Binocular Vision Enhances Target Detection by Filtering the Background
Authors: Schneider Bruce , Moraglia Giampaolo
Published: January 2007

In previous studies the authors have shown that the enhanced detectability exhibited by stereoscopically viewed targets can be accounted for by assuming that the binocular system can linearly summate the left-eye and right-eye views of a visual scene. A model based upon this assumption leads to a variety of predictions concerning the detectability of noise-embedded targets. One such prediction is that the detectability of a target in these conditions is highly orientation specific. A test is reported of such a prediction that can be regarded as counterintuitive: namely, that the detectability, under stereoscopic viewing conditions, of a patch of sinusoidal grating masked by Gaussian noise should change substantially when the grating, oriented at 45°, is rotated until its orientation becomes −45°. The implications of these results for an understanding of the phenomenon of camouflage breaking are discussed.
Binocular Perception of Slant about Oblique Axes Relative to a Visual Frame of Reference
Authors: van Ee Raymond , Erkelens Casper J
Published: January 2007

From the literature it is known that the processing of disparity for slant is different in the presence and in the absence of a visual frame of reference. The experimental finding that vertical disparity is not processed for slant perception in the presence of a visual reference is elaborated. This theoretical analysis results in a reduction of the three basic first-order transformations between the retinal half images (divergence, rotation, and deformation) to only two basic orthogonal transformations. The first of these, horizontal scale, results in slant perception about the vertical axis, whereas the second, horizontal shear, results in slant perception about the horizontal axis. These transformations are based primarily on horizontal disparity. It is shown experimentally that in the presence of a frame of reference the amount of vertical transformation that is added to the two basic transformations (horizontal scale and shear) of a random-dot stimulus is indeed irrelevant for slant perception. It is suggested that, in the presence of a visual reference, slant perception about oblique axes is based solely on linear combinations of the horizontal-scale and horizontal-shear transformations. Subjects are able to reproduce slants about oblique axes experimentally merely by combining horizontal scale and shear.
Parallel Independent Encoding of Orientation, Spatial Frequency, and Contrast
Authors: Vincent Alex , Regan David
Published: January 2007

Subjects were presented with a set of 216 test gratings in random order. Each had a different combination of orientation, spatial frequency, and contrast. For each test grating, subjects were instructed to judge whether or not orientation was clockwise of the mean of the stimulus set, whether or not spatial frequency was higher than the mean of the stimulus set, and whether or not contrast was higher than the mean of the stimulus set. Each of the three sets of button presses was analyzed with respect to each of the three parameters, giving nine psychometric functions from one response set. It is concluded that, for gratings of high visibility, changes of orientation, spatial frequency, and contrast are encoded independently and in parallel, at least for small changes in these three visual parameters. In another experiment only one of the three parameters was varied at a time. Neither orientation-discrimination threshold, nor spatial-frequency-discrimination threshold, nor contrast-discrimination threshold was appreciably, if at all, lower than when all three parameters were varied simultaneously. It is concluded that interactions between the processing of small changes in orientation, spatial frequency, and contrast are negligible when all three are processed simultaneously. It is proposed that trial-to-trial variations of orientation, spatial frequency, and contrast are unconfounded by opponent processing within a population of neurons, each of which confounds the three variables.
Judgment of Gender through Facial Parts
Authors: Yamaguchi Masami K , Hirukawa Tastu , Kanazawa So
Published: January 2007

Japanese male and female undergraduate students judged the gender of a variety of facial images. These images were combinations of the following facial parts: eyebrows, eyes, nose, mouth, and the face outline (cheek and chin). These parts were extracted from averaged facial images of Japanese males and females aged 18 and 19 years by means of the Facial Image Processing System. The results suggested that, in identifying gender, subjects performed identification on the basis of the eyebrows and the face outline, and both males and females were more likely to identify the faces as those of their own gender. The results are discussed in relation to previous studies, with particular attention paid to the matter of race differences.
Varying the Strength of the Munker—White Effect by Stereoscopic Viewing
Authors: Taya Raiten , Ehrenstein Walter H , Cavonius C Richard
Published: January 2007

In the Munker—White effect grey target bars appear lighter when they are flanked by white bars, and darker when they are flanked by black bars. It is shown that the effect is enhanced if the patterns are presented stereoscopically so that the grey bars appear either behind the grating, in which case they are seen as a rectangle that is occluded by the white bars of the grating, or in front of the grating, so that they form a transparent rectangle. These results are explained in terms of object perception: contrast enhances differences between an object and its surroundings, whereas assimilation reduces differences within an object.
Size Invariance in Visual Object Priming of Gray-Scale Images
Authors: Fiser József , Biederman Irving
Published: January 2007

The strength of visual priming of briefly presented gray-scale pictures of real-world objects, measured by reaction times and errors in naming, was independent of whether the primed picture of the object was presented in the same size as or different size from the original picture. These findings replicate results on size invariance in shape recognition, which were obtained with line drawings, and extend them to the domain of gray-level images. Entry-level shape identification is based predominantly on scale-invariant representations incorporating orientation and depth discontinuities which are well captured by line drawings.
Transparent Surfaces and Illuminated Holes
Authors: Masin Sergio Cesare
Published: January 2007

A single stimulus determined the alternative perceptions of an illusory transparent grey disk or of an internally illuminated circular hole. A square on a far background was visible through this disk or hole. Subjects rated the grey colour of the transparent disk or the phenomenal illumination inside the hole. The luminance difference relative to the transparent disk and the square and that relative to this disk and its background determined the probability of perceiving the transparent disk or the hole. Rated colour and illumination substantially depended only on this second difference. These results have implications for models of phenomenal transparency and illumination based on the idea that proximal contours activate neural representations of phenomenal attributes.
Size Constancy in Structure from Motion
Authors: Turner Jessica , Braunstein Myron L
Published: January 2007

The relative motions of points in a structure-from-motion display involving parallel projection provide depth information in an object-centered framework: differences in velocity do not reflect differences in distance from an eyepoint. In contrast, size constancy is generally regarded to be a perspective effect, based on the relationship between projected size and distance from an eyepoint. Five subjects judged the relative sizes of objects in structure-from-motion scenes. Although the scenes were displayed without perspective, judged size was related to the simulated separation in depth of the objects. These results suggest that relative depths recovered from object-centered information are incorporated into a viewer-centered framework.
A New Motion Illusion Related to the Aperture Problem
Authors: Bressan Paola , Vezzani Stefano
Published: January 2007

A previously unreported motion illusion is described. Oblique lines that drift smoothly on the retina in a vertical direction appear to be displaced laterally. The effect occurs both for moving lines under fixation and for stationary lines under ocular tracking of an external target. Orientation, length, and homogeneity of the obliques affect the magnitude of illusory displacement. We propose that this illusion is associated with a misregistration of the direction of displacement occurring, in lines slanted relative to the axis of their motion, because of the aperture problem.
Local-Level and Global-Level Form Characteristics in Apparent-Motion Correspondence
Authors: Palmer Terry , Tzeng Ovid J L , He Sheng
Published: January 2007

This study addressed the ‘correspondence’ problem of apparent-motion (AM) perception in which parts of a scene must be matched with counterparts separated in time and space. Given evidence that AM correspondence can be mediated by two distinct processes—one based on a low-level motion-detection mechanism (the Reichardt process), the other involving the tracking of objects by visual attention (the attention-based process)—the present study explored how these processes interact in the perception of apparent motion between hierarchically structured figures. In three experiments, hierarchical figures were presented in a competition motion display so that, across frames, figures were identical at either the local or the global level. In experiment 1 it was shown that AM occurred between locally identical figures. Furthermore, with the Reichardt AM component eliminated in experiments 3 and 4, no preference was obtained for either level. While evidence from previous studies suggests that form extraction for hierarchically structured figures proceeds from the global to the local level, the present results indicate the irrelevance of such a global precedence in AM correspondence. In addition, it is suggested that Reichardt AM correspondence between local elements constrains attention-based AM correspondence between global figures so that both components move in the same direction. It is argued that this constraining process represents an elegant means of achieving AM correspondence between objects undergoing complex transformations.
Categorical Local-Shape Perception
Authors: Mamassian Pascal , Kersten Daniel , Knill David C
Published: January 2007

How well do observers perceive the local shape of an object from its shaded image? This problem was addressed by first deriving a potential representation of local solid shape. The descriptor of local shape, called shape characteristic, provides a viewpoint-independent continuum between hyperbolic (saddle-shaped) and elliptic (egg-shaped) points. The ability of human observers to make categorical judgments of local solid shape was then studied. This question was investigated by using a smooth ‘croissant’, a simple object made of two connected regions of elliptic and hyperbolic points. Observers decided whether the surface was locally elliptic or hyperbolic at various points on the object. The task was natural, and the observers could reliably partition the shaded image of the object into two regions, one elliptic and one hyperbolic. The ability of observers to perform this partition shows that they can, at least implicitly, localize the parabolic curves on a surface. This ability to locate the parabolic curve could in turn be exploited for other purposes, for instance to segment an object into its parts.
Segregation of Motion Structure from Random Visual Noise
Authors: Ahlström Ulf , Börjesson Erik
Published: January 2007

A potential source of information about spatial layout, surface slant, and self-motion is provided by transformations of the optic flow field. Theoretical analyses have demonstrated that such flow fields can be decomposed into translation, rotation, expansion, and deformation components. The objective in this study was to investigate the effectiveness of these motions as visual primitives for preattentive scene segregation. The stimuli consisted of two-frame patterns containing 998 dots. A variable number of these dots (5 to 50) were defined as target dots, representing a specific motion structure, with the residual dots defined as a noise field. The observers' task was to identify the location and type of motion structure. On the basis of the number of target dots needed to detect and correctly identify the target structure, it was determined that translation was the most easily detected structure, followed by rotation, expansion, and compression. Deformation was found to have a detection threshold as high as compression. The results are related to other studies of these motion components.
Texture Laciness: The Texture Equivalent of Transparency?
Authors: Watanabe Takeo , Cavanagh Patrick
Published: January 2007

Displays with overlapping squares of different textures were produced. In some texture combinations, the overlapping area appears to be a new texture. In other combinations, however, one texture is seen through the other as if it were inscribed on a transparent sheet and held in front of the other. This phenomenon can be called texture laciness. It is claimed that texture laciness is important because in the natural world we frequently encounter overlapping textures that we perceive as separate. In examining the conditions that lead to texture laciness, it was found that (1) laciness occurs more strongly with decreasing similarity between elements of two textures, (2) when the elements of the two textures are the same, the overlapped area tends to appear as a new texture, and (3) the physical overlapping of the individual elements of two textures hinders texture decomposition, irrespective of relative positioning. It is suggested that the textures inducing laciness may be processed as surfaces rather than just collections of identical elements. Texture laciness also reveals that even if ‘antitextons’—the shapes of the spaces between texture elements, which have been regarded as important in texture discrimination — are destroyed by positioning another set of texture elements in the spaces, the textures can remain sufficiently identifiable to be perceived as separate.
Target Localisation and Identification in Rapid Visual Search
Authors: Saarinen Jukka
Published: January 2007

In recent models of visual search it has been proposed that, in rapid parallel search, information about the location of a target pattern among distractors and information about its identity would not be available simultaneously, but that target location is represented at earlier stages of visual processing than target identity. In the present study, the priority of location information over identity information in parallel visual search was investigated by means of one identification and two localisation tasks of different levels of difficulty. In all three tasks, the stimulus display was identical. An oblique line segment, randomly 45° or 135° in orientation, was presented randomly at one quadrant of the display. In the identification task, the observer reported the orientation of the oblique line irrespective of its location. In the easy localisation task, the observer indicated whether the oblique line was at the left or right side of the display, and in the difficult localisation task whether it was in the upper or lower part of the display. In both localisation tasks, the observer ignored the orientation of the target line. The oblique line was accompanied by one, five, seventeen, or thirty-nine vertical distractor line segments in all tasks. The results showed that the response speed in the left vs right localisation was faster than in the identification task, whereas performance in the up vs down localisation was inferior. When the response factors (stimulus–response compatibility) in the left vs right localisation were taken into account, there were no performance differences between localisation and identification. Thus, these results demonstrated that direct performance comparisons between localisation and identification may be somewhat arbitrary, and they do not solve the issue of priority of location or identity information in rapid visual search.
Line Drawings of Faces Reduce Configural Processing
Authors: Leder Helmut
Published: January 2007

The highly specialised skill of face recognition found in humans is thought to be dependent on the processing of a combination of edge-based and surface-based information, and of single-feature as well as of configural information. An investigation was carried out into how the saliency of facial information differs between faces presented as line drawings and the same faces presented as photographs. In experiment 1, the participants showed a decreased sensitivity in their detection of changed configural properties if the faces were presented as line drawings. In experiment 2 an investigation was carried out into whether distinctiveness due to configural properties loses its impact on recognition when faces are transformed to line drawings. For each of twenty unfamiliar male faces, a more ‘distinctive’ version was created by moving the eye region down. The increase of distinctiveness was confirmed in a rating phase. In a later recognition test, with the same stimuli presented either as line drawings or as photographs, the more distinctive stimuli produced higher recognition rates when presented as photographs but the advantage disappeared when the same faces were presented as line drawings. The changes in sensitivity to configural properties thus contribute to the poor recognition of faces presented as line representations.
Generalization to Novel Images in Upright and Inverted Faces
Authors: Moses Yael , Ullman Shimon , Edelman Shimon
Published: January 2007

An image of a face depends not only on its shape, but also on the viewpoint, illumination conditions, and facial expression. A face recognition system must overcome the changes in face appearance induced by these factors. Two related questions were investigated: the capacity of the human visual system to generalize the recognition of faces to novel images, and the level at which this generalization occurs. This problem was approached by comparing the identification and generalization capacity for upright and inverted faces. For upright faces, remarkably good generalization to novel conditions was found. For inverted faces, the generalization to novel views was significantly worse for both new illumination and viewpoint, although the performance on the training images was similar to that on the upright condition. The results indicate that at least some of the processes that support generalization across viewpoint and illumination are neither universal (because subjects did not generalize as easily for inverted faces as for upright ones) nor strictly object specific (because in upright faces nearly perfect generalization was possible from a single view, by itself insufficient for building a complete object-specific model). It is proposed that generalization in face recognition occurs at an intermediate level that is applicable to a class of objects, and that at this level upright and inverted faces initially constitute distinct object classes.
Meridional Anisotropy in the Discrimination of Parallel and Perpendicular Lines—Effect of Body Tilt
Authors: Chen Shuai , Levi Dennis M
Published: January 2007

It is well documented that orientation discrimination is poorer for stimuli oriented obliquely than for those that are vertical or horizontal. Buchanan-Smith and Heeley recently reported that in the absence of a spatial reference this anisotropy follows gravitational rather than retinal coordinates, suggesting a high-level basis for the anisotropy in unreferenced orientation discrimination tasks. In the present study, unlike the previous one, the effects of body tilt on orientation discrimination have been examined in the presence of explicit simultaneous spatial references. The thresholds for discrimination of two parallel or two perpendicular lines were estimated for the retinally principal and oblique orientations, with the body either erect or tilted 45° with respect to gravity. In agreement with previous studies, meridional anisotropy for both parallelism and perpendicularity discrimination was found when observers were seated upright. When the observer's body was tilted, the anisotropy for the parallelism task was mapped to retinal and not to gravitational coordinates after compensating for countertorsion. Initially, the anisotropy for the perpendicularity task was not mapped to retinal coordinates, but after extensive practice for both the erect and the tilted body conditions it eventually followed retinal coordinates. The results reported here suggest that contrary to orientation discrimination without a spatial reference, the ultimate limits for both parallelism and perpendicularity discriminations are located at orientation-sensitive cortical neurons. However, the effect of perceptual learning in the perpendicularity task suggests that the internal frame of reference (gravity cues and body axis) also plays an important role.
Visually Perceived Eye Level is Influenced Identically by Lines from Erect and Pitched Planes
Authors: Li Wenxun , Matin Leonard
Published: January 2007

The physical elevation that appears to correspond to eye level (VPEL), as measured with a small visual target, changes systematically with the orientation in depth (‘visual pitch’) of a visual field consisting of one or two pitched-from-vertical lines in darkness. The influence is large and, with a one-line stimulus, is only 15% smaller than the influence exerted by a complexly structured, well-illuminated, pitched visual field. A line from a frontoparallel plane can be presented to the same retinal locus as a pitched-from-vertical line; the three experiments in the present report were aimed at determining the influence on VPEL from such lines. In the first two experiments the subject viewed a visual field consisting of a one-line or two-line pitched-from-vertical stimulus from a pitched-only plane or an oblique one-line or two-line stimulus from an erect plane. Each of the pitched-from-vertical stimuli was presented at seven different orientations separated by 10° over a ±30° range. Each of the oblique-line stimuli was presented at an orientation that resulted in stimulation to the same retinal locus as one of the conditions with pitched-from-vertical lines, and thus a range of ‘equivalent pitches’ was examined that corresponded to the range of pitches for the pitched-from-vertical lines. The variation in orientation of the oblique-line stimulus and the pitched-from-vertical stimulus each produced systematic changes in VPEL; the two were indistinguishable. A third experiment specifically designed to examine the possibility that either stimulus sequencing or lack of naivity of the subjects might have been involved turned up no such effects. It is concluded that the aspect of a line stimulus that controls the influence on VPEL is the orientation of the image of the line on a projection sphere centered on the nodal point of the eye or, as in the present experiments with viewing in primary position, the retinal locus stimulated; the orientation-in-depth of the stimulating line provides no additional influence on VPEL for the stationary, erect, monocularly viewing observer. The results are interpreted within the framework of the great-circle model.
Pigeons Do Not Complete Partly Occluded Figures
Authors: Sekuler Allison B , Lee Jane A J , Shettleworth Sara J
Published: January 2007

One of the most common obstacles to object perception is the fact that objects often occlude parts of themselves and parts of other objects. Perceptual completion has been studied extensively in humans, and researchers have shown that humans do complete partly occluded objects. In an effort to understand more about the mechanisms underlying completion, recent research has extended the study of perceptual completion to other mammalian species. Monkeys and mice also seem to complete two-dimensional representations of partly occluded objects. The present study addresses the question of whether this capacity generalizes to a nonmammalian species, the pigeon ( Columba livia). The results point to a limit of the generalizability of perceptual completion: pigeons do not complete partly occluded figures.
On the Ancient History of the Direction of the Motion Aftereffect
Authors: Verstraten Frans A J
Published: January 2007

Scientists agree that Aristotle in his Parva Naturalia was the first to report a visual illusion known as the motion aftereffect (MAE). But there is less consensus as to who was the first to report the direction of the MAE. According to some, Aristotle only described the phenomenon without saying anything about its direction. Others have defended the position that Aristotle did report a direction, but the wrong one. Therefore, it has been suggested that Lucretius in his poem De Rerum Natura was the first to report the correct direction of the MAE. In this paper it is shown why and how it can be inferred that Aristotle did not write about the direction of the MAE, only about its occurrence. It is also argued that it is indeed likely that Lucretius was the first person to report the direction of the MAE. However, this is not as obvious as it might appear at first sight.
Ptolemy's Contributions to the Geometry of Binocular Vision
Authors: Howard Ian P , Wade Nicholas J
Published: January 2007

Ptolemy's Optics which was written in about the year 150 ad contains an account of the geometry of binocular vision which has been almost totally neglected in the vision literature. An English translation of the relevant passages from the Latin text in Lejeune (1956) is presented together with commentaries and a brief introduction.
Motion Perception: A Modern View of Wertheimer's 1912 Monograph
Authors: Sekuler Robert
Published: January 2007

Max Wertheimer's 1912 monograph on apparent motion is a seminal contribution to the study of visual motion, but its actual contents are not widely known. This article attempts to clarify what the monograph did and did not contribute, emphasizing links between Wertheimer's principal findings and the results of subsequent investigations of motion perception, including currently active lines of research. The topics discussed include Wertheimer's experimental tests of explanations for apparent motion; his work with motion phenomena that lie between succession and optimum motion; his studies of the influence of attention on motion; explorations of various forms of hysteresis and motion transparency; and Wertheimer's work with a motion-blind patient.
The Structural Framework of Pictorial Balance
Authors: Locher Paul , Gray Sharon , Nodine Calvin
Published: January 2007

Two experiments were performed to examine how the subjective balance of a painting is created by its structural features and to determine if balance influences the way people look at paintings. Stimuli consisted of sixteen reproductions of twentieth-century paintings varying in artistic style and a reconstructed less-balanced version of each. Participants in experiment 1 determined the location of the balance center of each composition, assigned ‘weights’ to the pictorial features which contributed to the location of the balance center, and rated the picture for balance. It was found that design and museum professionals and individuals untrained in the visual arts were in good agreement as to the structural framework underlying the balance organization of a painting. For all participants, disruption of the balanced organizations of the original compositions led to reliable shifts in the location of the perceived balance centers of the originals compared with their less-balanced perturbations. Additionally, it was observed that particular features as such were not the origin of the balance phenomenon; rather, judgments concerning the balance structure and its center were dependent on the global integration of information across a wide area of the display field, but especially from its central region. Last, the subtle changes in balance structure between versions resulted in lower ratings of balance being assigned to the less-balanced perturbations by the design professionals only; the other two participant groups evaluated overall balance of the versions as comparable. In experiment 2, eye movements of a different group of untrained individuals were recorded as they performed similar tasks on the art stimuli. It was found that disruption of the balance structure of the original representational but not abstract compositions resulted in different regions of the original and perturbed versions being visually explored. Findings of both experiments are related to theoretical notions of balance.
Glass Patterns: Some Contrast Effects Re-Evaluated
Authors: Dakin Steven C
Published: January 2007

The relative contrast of features is known to be important in determining if they can be grouped. Two manipulations of feature contrast have previously been used to criticise models of visual grouping based on spatial filtering: high-pass filtering and reversal of contrast polarity. The effects of these manipulations are considered in the context of the perception of Glass patterns. It is shown that high-pass filtering elements, whilst destroying structure in the output of low-pass filters, do not significantly disrupt the output of locally band-pass filters. The finding that subjects can perceive structure in Glass patterns composed of high-pass features therefore offers no evidence against such spatial filtering mechanisms. Band-pass filtering models are shown to explain the rotation of perceived structure in Glass patterns composed of opposite contrast features. However, structure is correctly perceived in patterns composed of two ‘interleaved’ opposite contrast patterns, which is problematic for oriented filtering mechanisms. Two possible explanations are considered: nonlinear contrast transduction prior to filtering, and integration of local orientation estimates from first-order and second-order mechanisms.
Homing in Virtual Environments: Effects of Field of View and Path Layout
Authors: Péruch Patrick , May Mark , Wartenberg Fredrik
Published: January 2007

Triangle completion (ie homing to the starting point after completing two legs of a triangle) is a widely used method for examining path-integration abilities in animals and humans. Two experiments are reported in which homing was used to examine the efficiency of purely visual mechanisms (eg optical flow) for spatial-information coding and integration. Adult observers had to complete triangles in an interactively simulated three-dimensional environment which consisted of two critical objects and a homogeneous set of white cylinders serving as background. Each participant completed twenty-seven triangles corresponding to a factorial combination of three geometrical fields of view (40°, 60°, or 80°) and nine triangle layouts (with variations of the first turning angle and the second leg). Homing performances revealed strong effects of triangle layout, but no effect of geometrical fields of view: variations in the amount of simultaneous visible spatial information did not influence the acquisition of spatial knowledge in the environments used. Applying the encoding-error model to the data revealed severe systematic errors of picking up directional information while moving through visually simulated environments. These results are discussed with respect to informational differences between situations of purely visual and nonvisual navigations in space.
The Effects of Coarseness of Quantisation, Exposure Duration, and Selective Spatial Attention on the Perception of Spatially Quantised (‘Blocked’) Visual Images
Authors: Bachmann Talis , Kahusk Neeme
Published: January 2007

The two objectives of the present article are (a) to present a brief overview of the effects of systematic variation of the spatial-scale value of quantisation and stimulus duration on the identification of original images that have been degraded by Harmon–Julesz type of image pixelisation by ‘blocking’ and (b) to report the results of two experiments where the effects of selective spatial precuing by local and global peripheral precues on the identification of quantised target stimuli have been studied. Both the overview and the new results reported here demonstrate some counterintuitive effects: (1) abrupt decrease in identification efficiency with only a minor change in the coarseness of quantisation over a critical value of pixels per stimulus; (2) a cost for valid attentional precuing with coarse-quantised images. If physical precues (exposed with stimulus onset asynchrony of 120 ms) were employed in order to orient spatial attention to perceive original or fine-quantised stimuli, then attentional facilitation was found. However, if the precued stimuli were coarse quantised then the facilitative effect crossed over to a detrimental effect of attention. These effects are discussed in the context of the microgenetic approach that presupposes the existence of a perceptual–attentional processing routine that operates according to the coarse-to-fine time-course rule of selective attentional activation of stimulus representations at various spatial scales.
Assimilation: Central and Peripheral Effects
Authors: de Weert Charles M M , van Kruysbergen Noud A W H
Published: January 2007

Assimilation and contrast have opposite effects: Contrast leads to an increase of perceived differences between neighbouring fields, whereas assimilation leads to a reduction. It is relatively easy to demonstrate these effects, but the precise localisation of these effects in the perceptual system is not yet possible. In an experiment the strength of assimilation effects was modified by adding spatial noise. By varying the localisation in perceived space of the added noise (by presentation of the noise pattern with different binocular disparities) the masking effect of this noise can be influenced. Masking caused by binocularly disparate noise is less than masking caused by binocularly non-disparate noise. It is concluded that the effect at least partly occurs beyond the (binocular) locus of separation in different depth planes. A similar approach, involving moving noise, is also presented. Finally, several demonstrations show that images that are peripherally similar can give rise to differences in the perceived amount of assimilation. These effects further indicate that a central mechanism is involved in assimilation.
Face Recognition with Multi-Tone and Two-Tone Photographic Negatives
Authors: Liu Chang Hong , Chaudhuri Avi
Published: January 2007

The effects of photographic negatives on face recognition are often studied in two different ways—faces are learned and tested in photographic negatives (NN) or the contrast is reversed between learning and testing, ie they are learned in positives and tested in negatives (PN) or vice versa (NP). We have examined recognition performance for faces under these three conditions along with a control condition where faces were learned and tested in positives (PP). Using multi-tone face images, we found that the effect of photographic negatives was more pronounced in PN and NP than in NN. No differences were found between PN and NP or between NN and PP. When two-tone face images were used, recognition performance was worse in all conditions, except PP, when compared to the multi-tone counterparts. Our results show that contrast incongruency between learning and testing is the predominant factor affecting performance and that deficits in sensory coding or retention of negative face images are unlikely to be major factors. The advantage of multi-tone over two-tone negatives can be attributed to preserved facial information carried by the high-spatial-frequency components of the image.
A Functional Rôle for Illusory Colour Spreading in the Control of Focused Visual Attention
Authors: Davis Greg , Driver Jon
Published: January 2007

In cases of modal completion, illusory colour spreading fills in the surface of a subjectively completed shape. In amodal completion, shapes are likewise completed, but now behind a partial occluder, so that filling in of illusory colour to the completed region no longer arises. We consider the possible functional effects that illusory colour spreading may exert on later stages of vision, and argue that comparisons of modal with amodal completion may be particularly revealing in this regard. It is hypothesised that cueing the inducers of a modally completed object should attract attention to the entire object, including the completed region, owing to the colour spreading there. By contrast, changes to the inducers of a comparable amodally completed object should only attract attention to the inducing regions themselves. This prediction is supported by findings in two experiments with stereoscopic displays, with control conditions ruling out nonattentional accounts, or explanations in terms of stereo disparity alone rather than the presence versus absence of illusory colour. We argue that illusory colours get filled in at quite early stages during modal completion, precisely so that later stages of vision, such as focused attention, can then be driven by the completed regions in the same way as for uniform regions that are physically present in the image.
Types of Size Disparity and the Perception of Surface Slant
Authors: Pierce Byron J , Howard Ian P
Published: January 2007

We examined (i) perceived slant of a textured surface about a vertical axis as a function of disparity magnitude for horizontal-size disparity, vertical-size disparity, and overall-size disparity; and (ii) interactions between patterns with various types and magnitudes of size disparity and superimposed or adjacent zero-disparity stimuli. Horizontal-size disparity produced slant which increased with increasing disparity, was enhanced by superimposed zero-disparity stimuli, and induced contrasting slant in superimposed or adjacent zero-disparity stimuli. Vertical-size disparity produced opposite slant (induced effect) which was reduced to near zero by a superimposed zero-disparity pattern and both patterns appeared as one surface. Adjacent vertical-size-disparity and zero-disparity patterns appeared as separate surfaces with a wide curved boundary. Overall-size disparity produced slant which was enhanced by a superimposed zero-disparity pattern and less so by a zero-disparity line, and induced more slant in a zero-disparity line than in a zero-disparity pattern. The results are discussed in terms of depth underestimation of isolated surfaces, depth enhancement, depth contrast, and the processing of deformation disparity.
Illusory-Contour Formation Affected by Luminance Contrast Polarity
Authors: He Zijiang J , Ooi Teng Leng
Published: January 2007

We report a new type of illusory contour (Illusory-O) whose formation is contingent upon the contrast polarity of its juxtaposed inducing elements being similar, ie both elements must either be positive or negative in contrast sign. To test the hypothesis that this contingency is primarily dictated by factors that determine amodal surface completion (occlusion) between the inducing elements we conducted a series of experiments employing known spatial properties of the amodal completion mechanism, to show that spatial conditions unfavorable to occlusion lead to a concurrent weakening of the Illusory-O formation. For instance, we found that when the juxtaposed inducing elements (solid rectangles) were spatially misaligned, or when their spatial separation increased, our observers rated the perception of the Illusory-O as reduced. We also showed that, in addition to using solid-form inducing elements, the Illusory-O can be induced by line terminals, as long as these lines respect the requirements of the amodal completion mechanism such as similar contrast polarity and spatial alignment. Then we demonstrated that the role of the amodal completion mechanism is not limited to our particular arrangement of inducing elements by showing that the formation of the illusory Necker cube also relies on similar contrast polarity. Finally, to explain why some illusory contours like the Illusory-O are dependent on contrast polarity while others (eg Kanizsa square) are not, we propose that the key rests upon the visual system's presumption of occlusion. That is, in forming the illusory contour, if the visual system infers that it is a byproduct of the inducing elements being occluded, then having inducing elements of similar contrast polarity becomes a prerequisite. This assumption can be traced to the occurrence in the real world where partially occluded objects usually have visible parts (on both ends) with similar contrast polarity. Along this line of thinking, we suggest a plausible neural circuitry that may be implemented to form both contrast polarity sensitive and insensitive types of illusory contours.
Reference Repulsion When Judging the Direction of Visual Motion
Authors: Rauber Hans-Jürgen , Treue Stefan
Published: January 2007

While humans are very reliable (ie give highly reproducible answers) when repeatedly judging the direction of a moving random-dot pattern (RDP) we find that their accuracy (ie the direction they so reliably report) shows systematic errors. To quantify these errors, we presented a complete set of closely spaced directions and mapped the directional misjudgments by asking subjects to compare the perceived direction of a moving RDP with the direction of a test line. The results show misjudgments of up to 9°, which are best accounted for by a tendency of the subjects to overestimate the angle between the observed motion and an internal reference direction.

A control experiment in which subjects had to judge the spatial distance between a point and a line demonstrates that these misjudgments are not confined to motion stimuli but rather seem to reflect a general tendency to overestimate the distance between a stimulus and a reference when they are close to each other.
Role of Spatial and Temporal Coincidence in Depth Organization
Authors: Kojima Haruyuki , Blake Randolph
Published: January 2007

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a black vertically oriented bar with two brackets immediately flanking this bar and placed in crossed or uncrossed disparity relative to the bar. A pair of thin white ‘bridging lines' could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in phase or out of phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied. Compared to conditions when the bridging lines were absent, depth judgments were markedly biased toward “in front” when bridging lines and brackets flashed in temporal phase; this bias was much reduced when the bridging lines and brackets flashed out of phase. This biasing effect also depended on spatial offset of lines and brackets. However, perception was uninfluenced by the lateral separation between object and brackets.
A Moving Cast Shadow Diminishes the Pulfrich Phenomenon
Authors: Price Theodore J , O'Toole Alice J , Dambach Kimberly C
Published: January 2007

It is demonstrated that the presence of a moving cast shadow diminishes the Pulfrich phenomenon. This complements previous work by Kersten, Knill, Mamassian, and Bülthoff [1996 Nature (London)379 31] indicating that visible cast shadows can override monocularly based cues to the perceived trajectory of a moving object. The present finding with the Pulfrich phenomenon indicates the effectiveness of shadows for overriding binocularly based cues to the perceived trajectory of a moving object.
A New Stereoscopic Illusion: Eyes Popping Out and Sinking in
Authors: Papathomas Thomas V , Morikawa Kazunori
Published: January 2007

A stereoscopic illusion is produced by manipulating the binocular disparity of the irises in stereo pairs of human faces. These stimuli elicit unnatural percepts of the irises popping out of the face or sinking in inside the head.