bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversals of Visual Depth Caused by Motion Parallax
Authors: Hayashibe Keikichi
Published: January 2007

The role of the velocity and direction of retinal movement in the determination of apparent depth from motion parallax was examined. Motion parallax was produced either by linking the movement of random-dots to head movement or by making this motion independent of the head movement. The results show that apparent depth was largely estimated from the velocity difference between the stimuli. The direction of retinal movement in the absence of head movement did not determine whether the pattern appeared to protrude or recede. Information about direction linked to head movement was able to stabilize protrusion/recession by providing a cue for the location of the fixation point. Depth reversal occurred less frequently in the presence than in the absence of head movement. When the fixation point shifted from the apparently protruding pattern to the apparently receding pattern, in both the presence and absence of head movement, depth reversal was readily observed.
Evidence for Independent Processing of Subjective Contour Brightness and Sharpness
Authors: Siegel Steven , Petry Susan
Published: January 2007

Subjective contours have been of considerable interest because of their importance to theories and physiological models of form perception. In particular, they have recently been characterized as the result of magnocellular cortical processing. There is, however, a paucity of parametric data relating to basic psychophysical parameters in this field.

Two experiments are reported in which the roles of subjective contour size, retinal eccentricity, and flicker rate in subjective contour salience were investigated. Eleven observers estimated subjective contour magnitude using an Ehrenstein configuration. Configurations ranging in size from 0.25 to 3 deg were presented to three retinal loci (fovea, 2 deg, and 4 deg) at flicker rates ranging from 5 to 15 Hz. Subjective contour brightness and distinctness were measured separately. Brightness was greatest at a subjective contour size of about 1.25 deg, at flicker rates of 5 – 7 Hz, and at 3 deg peripheral for all flicker rates and all but the smallest stimulus sizes. Distinctness decreased with eccentricity and flicker, but remained high at small diameters (thus implicating spatially sensitive mechanisms). Taken together, the results support a magnocellular processing of subjective contours with respect to brightness, but also suggest that there is a parvocellular contribution to subjective contour sharpness.
Illusory Figures Based on Local Kinematics
Authors: Bruno Nicola , Gerbino Walter
Published: January 2007

A new type of motion-induced illusory figure determined by local kinematic information is investigated. The new figure is induced by radial line patterns subjected to either figure motion (the lines change as if they were stationary and a triangle was rotating in front of them) or background motion (the lines change as if they were being rotated behind a stationary triangle). Although the two kinds of motion are equivalent from the viewpoint of relative displacements, perceptually they yield very different results. With background motion, observers tend to perceive rigid figures that have a triangular shape. With figure motion, observers report seeing deforming figures with shapes that vary depending on the number of lines in the display. We consider two alternative accounts for this asymmetry which we term the background superiority effect (BSE). The first account proposes that the effect is due to retinal persistence and to figure stability. Against this line of explanation, we demonstrate that observers also see rigid triangular shapes in displays where both the figure and the radial lines rotate (double motion displays). The second account proposes that the effect depends on the availability of local kinematic information constraining contour orientation. This second line of explanation is consistent with observers' reports of bowed edges in double motion displays rotating in phase or in counterphase. Candidate mechanisms for extracting local kinematic information are discussed.
Gender Differences in Apparent Motion Perception
Authors: Shechter Sima , Hillman Peter , Hochstein Shaul , Shapley Robert M
Published: January 2007

Distance disparity is a strong cue to element correspondence in apparent motion. Using a 2-AFC paradigm we have previously shown that shape similarity also plays a role. We now demonstrate a small gender difference in these effects: women are more sensitive to distance disparity, whereas men are more sensitive to differences in shape. Furthermore, in the competing presence of a shape cue, women's sensitivity to distance decreases while men's sensitivity is unaffected. These observations may be related to putative gender differences in the ‘form’ and ‘motion—spatial relations’ cortical pathways.
Shape Discrimination for Motion-Defined and Contrast-Defined form: Squareness is Special
Authors: Regan David , Hamstra Stanley
Published: January 2007

Shape discrimination was measured for: (i) two-dimensional rectangular targets that were perfectly camouflaged within a stationary pattern of random dots and rendered visible by relative motion of the dots, and (ii) similar dotted rectangles that were rendered visible by luminance contrast. Shape discrimination was disconfounded from size discrimination by requiring subjects to discriminate the aspect ratios of rectangles whose areas were altered independently of aspect ratio. When dot speed and contrast were both high, the aspect-ratio discrimination threshold was as acute for motion-defined (MD) rectangles as for contrast-defined (CD) rectangles and, at 2–3%, corresponded to a change of side length of about 24 s arc compared to a mean dot separation of 360 s arc. Discrimination of MD rectangles collapsed at low dot speeds and could not be measured at speeds less than about 0.03–0.08 deg s−1, but discrimination of CD rectangles was almost unaffected by dot speed. The aspect-ratio discrimination threshold was lowest for a square and progressively increased as the rectangle became more asymmetric. It is suggested that the visual system contains a mechanism that compares the separations of pairs of contours along different azimuths, and that, during visual development, this shape-discrimination processing of MD and CD targets is driven by the same environmental and behavioural pressures towards a common end point. The human equivalent of a pathway that includes the cortical area MT is thought to be important for shape discrimination of MD forms.
On the Salience of the Inducer's Displacement in Induced Rotary Movement
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

It has been reported that an annulus patterned with two equally-spaced radial lines elicits slower induced rotary movement than an annulus patterned with sixteen equally-spaced radial lines. This has been attributed to the quantity of inducing stimulation. However, the number of pattern elements also affects the time course of induced rotary movement: it can be intermittent with two-radii inducers, but persistent with sixteen-radii inducers. Displacement of a two-radii inducer may be more salient to the subject than displacement of a sixteen-radii inducer: from time to time the displacement of the former may come to dominate perception, suppressing induced movement. Hypotheses invoking quantity of stimulation and salience of inducer displacement were tested by way of inducers with different numbers and spacings of pattern elements. Subjects timed induced rotary movement (experiment 1) and a subsequent aftereffect (experiment 2). The results were consistent with both the quantity of stimulation (experiments 1 and 2) and the salience of inducer displacement (experiment 2) having an effect. This suggests that at least two mechanisms may be involved in induced rotary movement.
Influence of Physical and Semantic Information in a Categorisation Task of Fragmented Forms
Authors: Boucart Muriel , Bruyer Raymond
Published: January 2007

Two experiments were carried out to investigate the influence of structural and semantic information in the categorisation of visual forms. In experiment 1 the stimuli were pairs of ‘well structured’ or ‘poorly structured’ fragmented forms differing in structural properties including convexity, collinearity, and closure of the elements, and in their ‘name-ability’. The influence of structural and semantic information was tested by means of a task involving the presentation to both visual hemifields separately of stimuli having within-category physical similarity. For well structured forms, subjects were asked to judge if two sequentially presented forms belonged to the same semantic category. For poorly structured forms, subjects were required to decide if two stimuli belonged to the same previously learnt category of forms. For the two types of stimuli, one category was composed of physically similar items, and the other was composed of physically dissimilar items. The results show a marked advantage for the category composed of physically similar forms when the stimuli are well structured but no differences between the two categories when the stimuli are poorly structured. This suggests a facilitation in the computation of global shape information for forms having collinear and closed elements. The only effect of semantic information was a tendency towards a right visual field advantage for same-category pairs of well structured forms. The pattern of results for well structured fragmented forms (experiment 1) and forms in which fragments had been joined in order to complete the contour (experiment 2) were similar, suggesting that structured incomplete forms can be processed in the same way as forms having a continuous contour. Hypotheses about the organisational processes of forms are proposed in the discussion.
Thumb's Rule Tested: Visual Angle of Thumb's Width is about 2 Deg
Authors: O'Shea Robert P
Published: January 2007

Measures of the size of various hand parts and their viewing distance when held at arm's length were made on one hundred and eighteen undergraduate students. A simple rule of thumb can be confirmed: Visual angle of the width of the thumb held at arm's length is about 2 deg. The thumbnail subtends about 1.5 deg and the index fingernail about 1 deg in width, when both are held at arm's length. These figures are good approximations for males and females, although a significant, direct, linear relationship exists between hand-part size and the visual angle of the part at arm's length.
Orientation Disparity, Deformation, and Stereoscopic Slant Perception
Authors: Gillam Barbara , Rogers Brian
Published: January 2007

Koenderink and van Doorn's theory, that the basis of stereoscopic slant perception is the deformation component of the disparity, field, was tested for slant around a horizontal axis, which produces images with a vertical ramp of horizontal disparity (horizontal shear) characterised by a global orientation disparity at the vertical meridian. The disparity field in this case can be parsed into two components, deformation and curl, which each contribute half of the orientation disparity. This case was compared with similar random-dot stimuli in which the deformation component was doubled and the curl component eliminated or vice versa. All three types of stimuli had identical orientation disparity at the vertical meridian. A condition in which there was no such orientation disparity, but deformation was present, was also included. It was found that perceived slant was not related to the deformation present, as Koenderink and van Doorn's theory would predict, but was predictable from the orientation disparity at the vertical meridian per se.
Motion Adaptation from Surrounding Stimuli
Authors: Zaidi Qasim , Sachtler W L
Published: January 2007

When a narrow uniform gap was surrounded by a moving grating, the gap appeared as a grating in the opposite phase to that of the surround, moving in the same direction with the same speed. Contrast thresholds for moving test-gratings placed in the region of the uniform gap were found to be elevated after prolonged viewing of this pattern, thus demonstrating the existence of motion adaptation in a retinal region surrounded by, but not covered by, a moving pattern. The amplitude of the moving induced-grating was measured by nulling with a real grating moving in the same direction and with the same speed as the surround. When the speed of the inducing grating was varied, the amplitude of the induced effect did not correlate with the magnitude of the threshold elevation. Therefore, it is unlikely that motion adaptation in the uniform gap was due to induced gratings. In some conditions, the adaptation effect of surrounding gratings was no less than the adaptation effect of gratings covering the test region. This result rules out an explanation involving scattered light, and indicates that motion adaptation occurs at a later stage than that consisting of simple motion mechanisms which confound the contrast and velocity of a moving stimulus.
Attentional Modulation of a Figural Aftereffect
Authors: Shulman Gordon L
Published: January 2007

Evidence is reported that indicates that adaptation of the Schroder staircase is affected by attention. In previous work it has been shown that if subjects adapt to an unambiguous staircase, responses to an ambiguous test figure are biased towards the opposing perspective. In the current work, subjects adapted to superimposed upright and inverted Schroder staircases. Both staircases were centered on a common fixation point and were of different sizes and colors. Attention to each staircase was controlled by asking subjects to detect color changes in the line segments that defined one or the other staircase. Responses to an ambiguous test figure depended on which of the adapting staircases was attended.
Further Evidence of Failure of Reversal of Ambiguous Figures by Uninformed Subjects
Authors: Rock Irvin , Mitchener Kurt
Published: January 2007

In studying the reversal of ambiguous figures investigators understandably have always informed subjects of the reversibility of the figures and of how each version appears. However, such knowledge may be a cause of reversal and is therefore an undesirable aspect of the method used to study it. An experiment is described that is an improvement in some respects on a previously reported one in which subjects are not informed about reversal. The result was that only about a third of the subjects ever reversed. In a control condition the same subjects were informed in the traditional way and then not only did they always reverse but did so very frequently in the time period tested. Theoretical implications of these findings are discussed.
Reduced Spatial Sensitization on Nonuniform Backgrounds
Authors: Kurtenbach Anne , Spillmann Lothar
Published: January 2007

Spatial sensitivity (Westheimer) functions, when measured on nonuniform backgrounds made up of light dots of 12 min arc, were found to differ in shape, depending on the polarity of the central area on which the test spot was placed. When thresholds were measured on the dark centre between light dots, ie on the adapting-field illumination, the resulting curve was similar to the control curve, measured on a uniform background equated for flux. In comparison, thresholds measured on a central light dot, serving as a pedestal, peaked at larger background diameters and showed much less sensitization compared to the control function.
Use of Preferential Inspection to Define the Viewing Sphere and Characteristic Views of an Arbitrary Machined Tool Part
Authors: Perrett David I , Harries Mark H , Looker Simon
Published: January 2007

Measurements were made of the way human subjects visually inspected an idealized machined tool part (a ‘widget’) while learning the three-dimensional shape of the object. Subjects were free to rotate the object about any axis. Inspection was not evenly distributed across all views. Subjects focused on views where the faces of the object were orthogonal to the line of sight and the edges of the object were aligned parallel or at right angles to the gravitational axis. These ‘face’ or ‘plan’ views were also the easiest for subjects to bring to mind in a mental imagery task. By contrast, when subjects were instructed to imagine the views displaying the most structural information they visualized views lying midway between face views.
Higher-Order Factors Influencing the Perception of Sliding and Coherence of a Plaid
Authors: Kooi Frank L , De Valois Karen K , Switkes Eugene , Grosof David H
Published: January 2007

The effect of several new stimulus parameters on the perception of a moving plaid pattern (the sum of two sine-wave gratings) were tested. It was found that: (i) the degree of perceived sliding is strongly influenced by the aperture configuration through which the plaid is viewed; (ii) the chromaticity of the sinusoidal components affects coherence in that more sliding is observed when the plaid components differ in hue, and there is less sliding when they are of the same hue; (iii) equiluminant plaids made of components equal in color almost never show any sliding; and (iv) sliding increases with viewing time.

The coherence—sliding percept must therefore be influenced by color, by global interactions, and by adaptation or learning effects, thus suggesting a higher-level influence. These results are most easily modelled by separating the decision to carry out recombination from the process of recombination.
Resolving Ambiguities in Orientation, Motion, and Depth Domains
Authors: Allik Jüri
Published: January 2007

Three different perceptual systems—orientation, motion, and depth—can recover a global perceptual organization from spatially correlated random multielement patterns. In all three cases the global structure composed of random elements is evaluated by mechanisms performing measurements in the energy domain within appropriately defined local space—time areas. The selective increase in energy of one fraction of the elements may dramatically change the whole perceptual organization of the stimulus. In specially devised patterns one and the same element can belong to two or more separate perceptual organizations, the perceptual salience of one of which can be reinforced by a luminance increment of the elements comprising it. If a stimulus provides two different perceptual organizations to which each element could potentially belong, one of four possible solutions of the existing ambiguity will occur: suppression, rivalry, mixture, or parity. Two superimposed global orientation patterns either suppress or dominate over each other but cannot be seen simultaneously or in a mixed form. Characteristic of the depth system is that it allows multiple binocular matchings and parity of possible perceptual solutions. Finally, if a stimulus provides two or more paths along which each element may appear to move, the perceived global motion direction is determined by a mixture of directions of these competing motion paths. Dissimilarities in these ways of resolving ambiguities may be based on different principles defining regularity and coherence of an object in the orientation, motion, and depth domains.
Directional Bias in the Perception of Translating Patterns
Authors: Bertenthal Bennett I , Banton Tom , Bradbury Anne
Published: January 2007

Recent findings suggest that the visual system is biased by its past stimulation to detect one direction of motion over others. Three experiments were designed to investigate whether this bias is mediated by the direction or by the velocity of the past stimulation, and whether this bias is offset by contradictory pattern or depth information. Observers were presented with two solid or random-dot patterns that moved across a display screen in antiphase. As the two patterns reached the center of the screen, they became superimposed in such a way that their subsequent directions were ambiguous. Results from experiment 1 showed that the probability of perceiving these patterns as continuing to move in the same directions was significantly greater when they moved at a constant velocity than when they moved at a variable velocity. Results from experiments 2 and 3 revealed that this directional bias was reversed only gradually as an increasing amount of contradictory pattern information was introduced, but that this reversal was quite abrupt when a relatively small amount of contradictory depth information was introduced. Collectively, these results suggest that a directional bias in the perception of moving patterns is mediated not only by the direction of the previous stimulation, but also by the velocity of that stimulation. Moreover, the analyses of pattern and motion information appear relatively independent during the early stages of visual processing, but the analyses of depth and motion information appear considerably more interdependent.
The Perception of 3-D Rotation from Translating Sine-Wave Lines: The Reverse of the Barber-Pole Illusion
Authors: Ito Hiroyuki
Published: January 2007

An ambiguous moving pattern which gives rise to the reverse of the barber-pole illusion is reported. When vertical sine-wave lines translate, vertically and endlessly, on a two-dimensional (2-D) plane, one can perceive rotating three-dimensional (3-D) helixes without the impression of translation. With a single sine-wave line, 3-D rotation was seen for about half the exposure period. With three sine-wave lines shifted in phase by 120°, this illusion easily arose when one fixated a point near the endpoints of the lines, which moved horizontally and sinusoidally along the imaginery upper edge of the screen. When 3-D rotation was seen, the sine-wave lines which were intersecting on a 2-D display were perceptually decomposed into pairs of lines separated in depth. On fixating a point at the center of the figure, vertical translation was mainly seen. Foveal viewing of the horizontal sine movement of the endpoints of the lines produces the impression of 3-D rotation and the impression appears to provide some specific information towards solving the aperture problem and towards reconstructing the whole figure as such.
Perceptual Organization Evokes Simultaneous Lightness Contrast
Authors: Agostini Tiziano , Proffitt Dennis R
Published: January 2007

Principles of perceptual organization can cause simultaneous lightness contrast to be seen in patterns in which the inducing regions are not proximal to the target. In three experiments a match was made between two grey targets, one of which belonged to a white perceptual grouping and the other to a black one. In experiment 1, perceived belongingness was a product of common fate and figural alignment (columns of black dots and columns of white dots moved up and down in counterphase). In experiment 2, belongingness was evoked with only figural alignment. In experiment 3, belongingness was induced by common fate alone. In all three experiments it was found that the grey target belonging to the white group appeared darker than the grey target belonging to the black group.
Fraser Cords and Reversal of the Café Wall Illusion
Authors: Earle David C , Maskell Stephen J
Published: January 2007

Morgan and Moulden have shown that the café wall illusion can be explained by the effects of processing with a difference-of-Gaussians filter which reveals Fraser twisted cords in the figure. It is deduced that their account leads to the novel prediction of the reverse tilt illusion if the width of the mortar lines is suitably increased. This prediction is confirmed by demonstration.
Head Movement Changes Apparent Depth Order in a Motion-Parallax Display
Authors: Hayashibe Keikichi
Published: January 2007

The hypothesis that the apparent visual depth is determined by the proximal velocity relative to the position of the head was examined in three experiments. Apparent protrusion/recession changed when subjects observed a moving random-dot pattern with their heads tilted sideways or rotated in the horizontal plane. This is ascribed to lateral head movement, which increases the proximal velocity when the dots and the subjects' heads are moving in opposite directions, and decreases the proximal velocity when both are moving in the same direction. Changes in the direction of movement of the stimulus caused a reversal of the apparent protrusion/recession. The resultant proximal velocity of the stimulus determined the order of depth of surfaces when the movement of the stimulus was linked to the subject's head movement.
Size Induction Transcends the Cardinal Directions of Color Space
Authors: Rabin Jeff , Adams Anthony J
Published: January 2007

Certain psychophysical phenomena occur separately for color and for luminance stimulation. Separate psychophysical effects have also been elicited along different directions in equiluminant colour space. Whereas in most studies in which separate luminance and color effects have been reported the authors have used successive-adaptation approaches, less is known about the separateness of color and luminance processing under simultaneous conditions. A study is reported in which simultaneous size induction was examined for several different color directions thought to be ‘cardinal’ for early stages of processing. The perceived size of a test object was influenced by the size of the surrounding objects regardless of the color direction of the test and induction objects. The results indicate that simultaneous size induction occurs at a level of processing at which information conveyed by color and by luminance mechanisms is compared and contrasted to influence visual perception.
Representational Development of Direction in Motion Perception: A Fragile Process
Authors: Sekuler Allison B , Sekuler Robert
Published: January 2007

Response to a change in direction is more rapid if the target moves in a predictable direction before the change than if the pre-change direction is not predictable. However, if the target trajectory is viewed for approximately half a second before the change in direction, the effect of directional predictability disappears. Visual information gathered prior to change in direction is used to construct an increasingly more accurate representation of target trajectory. To study this process, we inject various temporal transients into the trajectory prior to the change in direction. We find that extraction of directional information is interrupted if: (i) motion continues along a constant trajectory, but the target disappears briefly behind an implicit or real occluder, (ii) the target pauses briefly, but remains visible, or (iii) the target changes speed briefly, while continuing to move in the same direction. The theoretical implications for motion perception are discussed. These implications include a framework for understanding interactions between stimulus-derived information and a priori information.
Parallel Visual Coding in Three Dimensions
Authors: Humphreys Glyn W , Keulers Nicole , Donnelly Nick
Published: January 2007

Evidence from visual-search experiments is discussed that indicates that there is spatially parallel encoding based on three-dimensional (3-D) spatial relations between complex image features. In one paradigm, subjects had to detect an odd part of cube-like figures, formed by grouping of corner junctions. Performance with cube-like figures was unaffected by the number of corner junctions present, though performance was affected when the corners did not configure into a cube. It is suggested from the data that junctions can be grouped to form 3-D shapes in a spatially parallel manner. Further, performance with cube-like figures was more robust to noncollinearity between junctions than was performance when junctions grouped to form two-dimensional planes. In the second paradigm, subjects searched for targets defined by their size. Performance was affected by a size illusion, induced by linear-perspective cues from local background neighbourhoods. Search was made more efficient when the size illusion was consistent with the real size difference between targets and nontargets, and it was made less efficient when the size illusion was inconsistent with the real size difference. This last result occurred even though search was little affected by the display size in a control condition. We suggest that early, parallel visual processes are influenced by 3-D spatial relations between visual elements, that grouping based on 3-D spatial relations is relatively robust to noncollinearity between junctions, and that, at least in some circumstances, 3-D relations dominate those coded in two-dimensions.
Visual Separability: A Study on Unschooled Adults
Authors: Kolinsky Régine , Morais José , Verhaeghe Arlette
Published: January 2007

It has been suggested in previous studies that unschooled adults present serious difficulties at performing tasks which, like part verification, dimensional filtering, or orientation judgments, require them to pay attention to a specific aspect of the stimulus structure. In the present study we examined the performance of unschooled adults by using a task which does not explicitly require the subjects to attend selectively to a specific component of the stimuli. Separability either of parts or of dimensions as well as line-orientation registration were estimated by the occurrence of illusory conjunctions. Whatever the properties involved in the illusions, these occurred in unschooled adults, at about the same rate as in age-matched schooled controls. The two sets of contrasting findings suggest that a critical variable is whether or not the subjects' attentional control is required. The relevance of the present findings as regards the level of processing responsible for illusory conjunctions is discussed.
Object Recognition under Sequential Viewing Conditions: Evidence for Viewpoint-Specific Recognition Procedures
Authors: Lawson Rebecca , Humphreys Glyn W , Watson Derrick G
Published: January 2007

In many computational approaches to vision it has been emphasised that object recognition involves the encoding of view-independent descriptions prior to matching to a stored object model, thus enabling objects to be identified across different retinal projections. In contrast, neurophysiological studies suggest that image descriptions are matched to less abstract, view-specific representations, resulting in more efficient access to stored object knowledge for objects presented from a view similar to a stored viewpoint. Evidence favouring a primary role for view-specific object descriptions in object recognition is reported. In a series of experiments employing line drawings of familiar objects, the effects of depth rotation upon the efficiency of object recognition were investigated. Subjects were required to identify an object from a sequence of very briefly presented pictures. The results suggested that object recognition is based upon the matching of image descriptions to view-specific stored representations, and that priming effects under sequential viewing conditions are strongly influenced by the visual similarity of different views of objects.
The Effect of Knowledge of Object Distance on Accommodation during Instrument Viewing
Authors: Kotulak John C , Morse Stephen E , Wiley Roger W
Published: January 2007

We present data in which instrument accommodation was measured while knowledge of object distance was varied. The accommodative feedback loop was ‘semiopen’—an intermediate state between the closed-loop and open-loop conditions of previous experiments. The semi-open-loop situation mimicked the degraded-image conditions which are frequently encountered during instrument viewing. The results show that for some subjects knowledge of object distance is a more powerful cue for instrument accommodation than is the optical distance of the object; however, for the majority of subjects this is not the case. We also found that subjects whose accommodation is influenced by knowledge of object distance tend to have a more proximal dark focus than those whose accommodation is independent of knowledge of object distance. We propose that the Mandelbaum effect, in which involuntary accommodation occurs when a transparency is superimposed between the observer and the object of regard, could account for the accommodative behavior of all subjects. However, the Mandelbaum effect would have to be interpreted more broadly than before. In the broader interpretation, the transparency could be cognitive (ie known distance) rather than physical.
The Contribution of Motion, the Visual Frame, and Visual Polarity to Sensations of Body Tilt
Authors: Howard Ian P , Childerson Laura
Published: January 2007

Three types of visual information contribute to the sense of self orientation with respect to gravity: visual polarity of objects with a distinct top and bottom, the principal vertical and horizontal lines of the visual environment, and visual motion. Three visual displays were designed to investigate the contribution of each visual feature to illusory self tilt: a large sphere lined with dots, a cubic room lined with dots, and a furnished room with floor and ceiling. In experiment 1 the dotted room and the furnished room were tilted to various angles about the roll axis of the erect subject who set a visual line and an unseen rod to the apparent vertical. In the dotted room, settings were made either with respect to the nearest surface to the horizontal or with respect to the nearest diagonal of the room. In the furnished room, settings were made with respect to the nearest horizontal wall but not with respect to diagonals. In experiment 2 each of the three displays was rotated at constant velocity and subjects' responses were classified into four categories: illusory self tilt at a constant angle, alternating self tilt with the body becoming erect each time a surface became horizontal, continuous head-over-heels self rotation, and a feeling that the body was supine. Almost all responses were of constant tilt in the sphere. Constant and alternating tilt were the most common responses in the dotted room. In the furnished room 60% of subjects experienced full head-over-heels self rotation.
Perception of Motion in Depth from Luminous Rotating Spirals: Directional Asymmetries during and after Rotation
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

Motion aftereffect (MAE) following spiral rotation is often asymmetrical: centrifugal MAE exceeds centripetal MAE. Pronounced MAE asymmetry has been reported for conditions—especially with a minimal background pattern—promoting perception of motion in depth. Such conditions are predicted to elicit motion asymmetry during adaptation. In the present study observers viewed luminous spirals monocularly in the dark; they timed, and scaled for convincingness, motion in depth during and after rotation. Motion in depth during rotation was often almost continuous, but recession was more convincing than was approach. Approaching MAE lasted longer and was more convincing than was receding MAE: the duration difference was more pronounced than has been found in other MAE studies, corroborating the link between MAE asymmetry and motion in depth. A possible line of explanation resides in comparing spiral motion in depth with real motion in depth of objects: in particular, the rapid visual change and collision with the observer that characterises real approach of an object is lacking in spiral approach. Interspecies differences for ‘looming’ and MAE are discussed.
Facial Aesthetics: Babies Prefer Attractiveness to Symmetry
Authors: Samuels Curtis A , Butterworth George , Roberts Tony , Graupner Lida , Hole Graham
Published: January 2007

The visual preferences of human infants for faces that varied in their attractiveness and in their symmetry about the midline were explored. The aim was to establish whether infants' visual preference for attractive faces may be mediated by the vertical symmetry of the face. Chimeric faces, made from photographs of attractive and unattractive female faces, were produced by computer graphics. Babies looked longer at normal and at chimeric attractive faces than at normal and at chimeric unattractive faces. There were no developmental differences between the younger and older infants: all preferred to look at the attractive faces. Infants as young as 4 months showed similarity with adults in the ‘aesthetic perception’ of attractiveness and this preference was not based on the vertical symmetry of the face.
Tactual Object Exploration and Recognition in Blind and Sighted Children
Authors: Morrongiello Barbara A , Humphrey G Keith , Timney Brian , Choi Jean , Rocca Patrick T
Published: January 2007

Development of the haptic system was evaluated by examining object exploration and recognition in sighted children between the ages of 3 and 8 years. To determine the importance of visual experience for these abilities, the performance of seven congenitally blind children was compared with that of sighted peers matched for age and gender. Performance was evaluated in terms of the speed and correctness of object identification, thoroughness of exploration of object parts, representation of the global form versus local parts of objects, and the possible role of critical parts in object identification. Four types of common objects were presented: normal-sized, miniaturized small, miniaturized large, and oversized objects. All subjects were required to manipulate and identify these objects haptically, without the aid of vision. Results revealed the emergence of a developmental pattern in all performance measures for sighted children. Older sighted children were not only able to recognize more objects and to do so more quickly, but also were more thorough in their exploration patterns. With increasing age, children appear to change their representation of objects from one based predominantly on global shape to one that incorporates a balance of global shape and specific local parts. In agreement with this, critical parts also played a role in object identification, particularly in older children. Blind and sighted children did not differ in any performance measures, which suggests that previous visual experiences do not determine tactile exploration strategies and are not essential for haptic object recognition.
Trade-Off between Achromatic Colour and Perceived Illumination as Revealed by the Use of Pseudoscopic Inversion of Apparent Depth
Authors: Logvinenko Alexander , Menshikova Galina
Published: January 2007

The albedo hypothesis was tested under apparent transformations of perceived illumination and achromatic colour induced by pseudoscopic inversion of apparent depth.

Looking through a pseudoscope made a cone attached to a vertical white screen look like a conical hole in the screen. This in turn caused the shadow which the now ‘invisible’ cone cast on the screen to change its appearance and to look like a darkly pigmented area. The darkness of the shadow before the pseudoscopic reversal and greyness of colour afterwards were measured by means of psychophysical scales for darkness and greyness set by the bisection method. Contrast of the shaded area was varied from 0.17 to 0.96 in 7 steps, the mean illuminance of the screen having been maintained at 40 lx.

Although the albedo hypothesis in its classical form was not confirmed, it was found that darkness of shadow varied linearly in inverse proportion to greyness of colour within the entire contrast range. This is in agreement with the hypothesis that achromatic colour and perceived illumination are inversely proportional to each other while the retinal illumination is constant.
Visual Directions of Two Stimuli in Panum's Limiting Case
Authors: Nakamizo Sachio , Shimono Koichi , Kondo Michiaki , Ono Hiroshi
Published: January 2007

Visual directions of the two stimuli in Panum's limiting case with different interstimulus and convergence distances confirmed the predictions from the reformulated Wells—Hering's laws of visual direction. In experiment 1, six observers each converged on the midpoint of the interstimulus axis at 30, 60, and 90 cm from the eyes and adjusted a probe on the fixation plane to be in the same visual direction as that of each stimulus. Visual direction of the far stimulus was always nonveridical whereas that of the near stimulus was veridical only when its retinal disparity was small. In experiment 2, three observers each converged on the intersection of mid-sagittal plane and (a) the frontoparallel plane of the near stimulus, (b) that of the midpoint between the two stimuli, or (c) that of the far stimulus. The midpoint of the interstimulus axis was 60 cm from the eyes. Visual direction of the far stimulus was veridical only with convergence at the far plane. Visual direction of the near stimulus was veridical with convergence at the near plane, and also, only when its retinal disparity was small, with convergence at the two other planes.
Aftereffects of Apparent Motion: The Existence of an AND-Type Binocular System in Human Vision
Authors: van Kruysbergen Noud A W H , de Weert Charles M M
Published: January 2007

There has been evidence for the existence of a purely binocular system in human vision that acts as an AND gate on information from the two eyes. There also has been evidence for the nonexistence of such a purely binocular system, indicating only the existence of an OR-type binocular system that responds to input from one or both eyes. As a result there are a number of possible explanations for the differing experimental results: the binocular system is an OR-type system only, it is a facilitating OR system that has AND-type characteristics, or it consists of independent OR and AND subsystems. Monocular adaptation, alternating monocular adaptation, or binocular adaptation were used to demonstrate the existence of the different systems, but in none of the previous experiments was the AND-type binocular system activated directly, and the existence of this AND system was deduced mostly because of differences in aftereffect strengths between monocular and binocular test conditions.

Experiments are reported in which stimuli that activate the AND-type binocular system explicitly have been used, and the results show that we need the existence of such an AND-type binocular system to account for the results.
Interocular Transfer of Expansion, Rotation, and Translation Motion Aftereffects
Authors: Steiner Vicki , Blake Randolph , Rose David
Published: January 2007

The motion aftereffect demonstrates the existence of direction-selective mechanisms in the visual system. However, direction-selective cells exist within many visual areas, including V1 and MT/V5. Can motion aftereffects be generated within each of these areas? In visual cortical areas beyond V1 almost all cells are binocular, whereas a smaller percentage are binocular in V1. The degree of binocularity can be revealed psychophysically by assessing interocular transfer. Interocular transfer of motion aftereffects generated from expanding, rotating, and translating dynamic random-dot patterns were therefore compared, since these stimuli should activate cells in higher visual areas selectively. Partial interocular transfer was found that was greater for expansion and rotation than for translation. The results support the involvement of higher visual areas in motion aftereffects to complex animation sequences.
Frames of Reference and Motion Aftereffects
Authors: Swanston Michael T
Published: January 2007

Evidence concerning the origin of the motion aftereffect (MAE) is assessed in terms of a model of levels of representation in visual motion perception proposed by Wade and Swanston. Very few experiments have been designed so as to permit unambiguous conclusions to be drawn. The requirements for such experiments are identified. Whereas retinocentric motion could in principle give rise to the MAE, data are not available which would enable a conclusion to be drawn. There is good evidence for a patterncentric origin, indicating that the MAE is primarily the result of adaptation in the systems responsible for detecting relative visual motion. There is evidence for a further contribution from the process that compensates retinocentric motion for eye movements, in the form of nonveridical information for eye movements. There may also be an effect at the level at which perceived distance and self-movement information are combined with egocentric motion to give a geocentric representation which provides the basis for reports of phenomenal experience. It is concluded that the MAE can be caused by changes in activity at more than one level of representation, and cannot be ascribed to a single underlying process.
Neuronal Mechanisms Underlying Stereopsis: How Do Simple Cells in the Visual Cortex Encode Binocular Disparity?
Authors: DeAngelis Gregory C , Ohzawa Izumi , Freeman Ralph D
Published: January 2007

Binocular neurons in the visual cortex are thought to form the neural substrate for stereoscopic depth perception. How are the receptive fields of these binocular neurons organized to encode the retinal position disparities that arise from binocular parallax? The conventional notion is that the two receptive fields of a binocular neuron have identical shapes, but are spatially offset from the point of retinal correspondence (zero disparity). We consider an alternative disparity-encoding scheme, in which the two receptive fields may differ in shape (or phase), but are centered at corresponding retinal locations. Using a reverse-correlation technique to obtain detailed spatiotemporal receptive-field maps, we provide support for the latter scheme. Specifically, we show that receptive-field profiles for the left and right eyes are matched for cells that are tuned to horizontal orientations of image contours. However, for neurons tuned to vertical orientations, the left and right receptive fields are predominantly dissimilar in shape. These results show that the striate cortex possesses a specialized mechanism for processing vertical contours, which carry the horizontal–disparity information needed for stereopsis. Thus, in a major modification to the traditional notion of the neural basis of stereopsis, we propose that binocular simple cells encode horizontal disparities in terms of phase at multiple spatial scales. Implications of this scheme are discussed with respect to the size–disparity correlation observed in psychophysical studies.
Binocular Disparity Processing with Opposite-Contrast Stimuli
Authors: Cogan Alexander I , Kontsevich Leonid L , Lomakin Alex J , Halpern D Lynn , Blake Randolph
Published: January 2007

Stereoscopic perception of relative depth with reversed-contrast half images differs in several important respects from stereopsis with matched-contrast half images. Thus, reversed-contrast images show no correlated shift in visual direction, indicating that the sensory-fusion mechanism ignores opposite-sign edges; one experiment addressed this aspect of the problem. Mainly, this was a quantitative study of opposite-contrast stereopsis, in which stereoacuity was measured as a function of bar width by means of narrow-band stimuli. Acuity was about an order of magnitude worse for reversed-contrast than for matched stimuli, but the ability to see valid (disparity-dependent) depth was not altogether lost even with wide (1 cycle deg−1) reversed-contrast bars. It is generally believed that depth with opposite-contrast stimuli is mediated by interaction between binocular stimuli components that have the same sign of contrast. Perceived depth was measured as a function of disparity and thus one of the predictions of that ‘same-sign hypothesis’ was tested experimentally; then, the magnitude of same-sign components was manipulated within the reversed-contrast stimuli, and thus the general prediction of the same-sign hypothesis was tested. The results show conclusively that the same-sign hypothesis cannot account for opposite-contrast stereopsis; its mechanism remains unknown.