bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Linear Vection on Manual Aiming at Memorized Directions of Stationary Targets
Authors: Lepecq Jean-Claude , Jouen François , Dubon Denise
Published: January 2007

Stationary observers were required to aim manually at either a straight-ahead, or a lateral, immobile target (0° and 20° of eccentricity, respectively). First, they aimed at a perceptually present target. Second, they aimed at the memorized direction of the target. Third, they aimed at the memorized direction of the target after a 4 s period of forward sagittal vection. The comparisons of the post-vection versus ante-vection aimings at the memorized direction of the targets reflect an illusory increase in the eccentricity of the lateral target, and no change in the direction of the straight-ahead target. These results objectivate the idea that forward sagittal vection (a particular case of linear vection) corresponds to an illusion of self-displacement, ie an illusory change of body place through space.
The Role of Parts and Spatial Relations in Object Identification
Authors: Cave Carolyn Backer , Kosslyn Stephen M
Published: January 2007

An investigation of the role of parts and their spatial relations in object identification is reported. At the most general level, two important results were obtained. First, proper spatial relations among components of an object are critical for easy identification. When parts were scrambled on the page, naming times and error rates increased. And, second, the way an object is divided into parts (parsed) affects identification only under the most impoverished viewing conditions. When subjects had as little as 1 s (and sometimes as little as 200 ms) to view an object, the way objects were divided into parts had no effect on naming times or accuracy. There was no hint of an interaction between type of parse and how parts were arranged on the page. This pattern of effects supports theories that suggest that objects typically are recognized without being parsed into parts. The findings are in agreement with theories suggesting that object features (not specifically related to parts) are matched directly with such features stored in long-term memory, with the constraint that the features of a single object are seen from a single viewpoint.
When Two is One: A Case Study of Spatial Parsing in Visual Neglect
Authors: Halligan Peter W , Marshall John C
Published: January 2007

In ‘left’ neglect—a frequent consequence of damage to posterior areas of the right cerebral hemisphere—the relational term ‘left’ immediately raises the question ‘left of what?’. It is shown that on a simple copying task the answer can be ‘left of the principal axis of the object or objects depicted’. Under conditions in which the stimulus material was intrinsically controlled for lateral extent and position, ‘object-centred’ neglect seemed to reflect some basic principles of perceptual parsing.
Structural Constraints: Further Evidence from Apparent Motion in Depth
Authors: Hershenson Maurice
Published: January 2007

The three-dimensional (3-D) apparent motion of lines, outline triangles, and light points was studied in four experiments. The stimulus sequences were beginning and end patterns of 3-D motions of a line and a triangle. Light-point patterns corresponded to the ends of the lines and the vertices of the triangles. Perceived motion of lines and light-point pairs resembled the distal motions that were used to construct the proximal patterns. The correspondence was striking for configurations that appeared to move in depth. Outline triangles and light-point triplets produced a strong correspondence between distal and perceived motions when the three sides appeared to be translating in depth. The correspondence was reasonably good for the other motion patterns when scoring included an appropriate second category. The results support the conception of structural or internalized constraints: light points were processed as if they were connected (unity constraint) and proximal change in linear size (or distance between light points) was perceived as rigid 3-D motion (rigidity constraint).
Illusion Decrement and Transfer of Illusion Decrement in Müller-Lyer Figures
Authors: Predebon John , Stevens Kate , Petocz Agnes
Published: January 2007

In the work reported in the literature the reduction or decrement in the magnitude of the Müller-Lyer illusion with continued inspection has been typically investigated with the use of the composite illusion form. Three experiments are reported in which the illusion decrement was separately examined in the underestimated (wings-in) and the overestimated (wings-out) forms of the Müller-Lyer illusion, with particular attention paid to the transfer of illusion decrement between the two forms. Decrement occurred in both forms of the Müller-Lyer illusion, although there was considerable intersubject variability in decrement effects, and nonuniform rates of decrement across the inspection period. In none of the experiments did transfer of illusion decrement between the two forms occur. It is argued that the attentional/differentiation hypothesis of illusion decrement provides a plausible account of the present findings as well as of those found with the composite Müller-Lyer figure.
Masking, Information Integration, and Tactile Pattern Perception: A Comparison of the Isolation and Integration Hypotheses
Authors: Mahar Douglas P , Mackenzie Brian D
Published: January 2007

Two competing models of the effects of pattern element proximity, masking, and perceptual integration on the discriminability of spatiotemporal vibrotactile patterns are compared. Kirman's ‘integration hypothesis' predicts that pattern perception is facilitated by a process of perceptual integration which requires that pattern elements be presented in close spatial and temporal proximity. Conversely, the ‘isolation hypothesis' predicts that the strong masking effects which occur when pattern elements are presented in close proximity impede the perception of patterns. Traditional masking studies do not provide a fair test of these two hypotheses because they rely on methods that measure the subject's ability to identify the target when the target is presented in conjunction with the mask, rather than the discriminability of the complex percept resulting from the integration of the target and mask. To account for this, a new procedure was devised where the amount of interelement masking and the discriminability of the pattern as a whole were measured independently as the spatial and temporal separation of the pattern elements were varied. As expected under both hypotheses, masking between pattern elements increased as either the spatial or the temporal separation between them was decreased. The pattern discrimination data also support the isolation hypothesis in that the patterns were discriminated less well with increasing temporal element separation with a similar but nonsignificant trend in the case of spatial separation. It is concluded that this new methodology should be applied to a wider range of tactile pattern processing situations in order to assess the generality of the results obtained.
Estimates of Time to Contact Based on Changing Size and Changing Target Vergence
Authors: Heuer Herbert
Published: January 2007

Apparent constant-velocity approaches of an outline circle were generated by changing the size and/or the lateral separation of dichoptically presented circles at a physically constant distance from subjects. The lateral separation of the circles defines target vergence which corresponds proximally to combinations of ocular vergence and (absolute) retinal disparity. In the first experiment, estimates of time to contact were found to depend both on changing size and on changing target vergence; in the case of conflicting information, changing size turned out to be the more powerful stimulus. In the second experiment, the size of the stimulus object was varied. The relatively stronger influence of changing size on estimates of time to contact was again found for the larger stimulus objects, but for the smaller stimulus objects changing target vergence became more powerful. The results of both experiments show that estimates of time to contact are not uniquely determined by changing size, as seems to be implied by some tests of the so-called ‘tau hypothesis’, but that they are based on multiple sources of information that have situationally specific effects on the estimates.
Effect of Depth Information on a Bistable Spiral-Motion Aftereffect
Authors: Wright Richard D , Day Russell W C
Published: January 2007

Two types of spiral-motion aftereffects were elicited by a single pattern: subjects reported seeing the pattern expand in the two-dimensional viewing plane or bulge toward them in three-dimensional space. Under binocular-viewing conditions reports of two-dimensional translations predominated. But when depth information was restricted under monocular-viewing conditions, reports of three-dimensional translations were more frequent. It appears that the bistability of these aftereffects can be influenced by the degree of depth information available about a stimulus pattern.
Hand Movements and Hemispheric Specialization in Dichhaptic Explorations
Authors: Fagot Joël , Hopkins William D , Vauclair Jacques
Published: January 2007

Dichhaptic testing has been widely used to assess lateralization in tactile processing. The rationale of dichhaptic testing is that simultaneous exploration of two objects enhances competition between relevant cortical areas in the right and left hemispheres. The synchronization of hand movements in a dichhaptic situation was investigated to determine whether both hands explore the two shapes simultaneously. Fourteen men were tested with the aid of a dichhaptic intermodal task. Tactile stimuli were composite shapes and the activity of each hand was assessed through analysis of hand contacts on each part of the shape. Only 20% of the total exploration time was devoted to simultaneous investigation of the two shapes. In addition, it was found that (i) the recognition accuracy was greater when the target shape was explored by the left hand compared with the right, and (ii) the left hand touched a greater number of parts of the stimuli than the right. Overall, comparison of the present data with those from a previous, monohaptic, task with the same stimuli suggests an advantage of dichhaptic over monohaptic testing to demonstrate laterality differences in accuracy of recognition. However, it is suggested that this advantage is due to cognitive factors rather than to competition between homologous cortical areas.
Mirror Reversals: Real and Perceived
Authors: Ittelson William H
Published: January 2007

A mirror optically reverses the axis perpendicular to its surface, but apparent reversals (eg right—left) can be seen parallel to the surface. This poses a perceptual problem which Ittelson, Mowafy, and Magid resolved by concluding that an object appears to differ from its mirror image by an apparent reversal along its axis of greatest symmetry. Three papers—two included in this discussion (by Haig and by Morris), and an earlier one by Gregory—that disagree with this conclusion are examined, and arguments advanced in them are shown to be unconvincing. The question of apparent mirror reversals is then discussed in more detail.
Reflections on Inversion and Reversion
Authors: Haig Nigel D
Published: January 2007

A paper published recently in Perception has drawn attention to a question that appears to mystify psychologists, yet yields simply to the well-known law of reflection. The question of why a mirror reverses left and right, but not up and down, is explained in this paper, in terms of physical optics. The question of how mirror-reflected objects are perceived remains, of course, a psychological one.
How is Depth Perception Affected by Long-Term Wearing of Left-Right Reversing Spectacles?
Authors: Ichikawa Makoto , Egusa Hiroyuki
Published: January 2007

The plasticity of binocular depth perception was investigated. Six subjects wore left-right reversing spectacles continuously for 10 or 11 days. On looking through the spectacles, the relation between the direction of physical depth (convex or concave) and the direction of binocular disparity (crossed or uncrossed) was reversed, but other depth cues did not change. When subjects observed stereograms through a haploscope and were asked to judge the direction of perceived depth, the directional relation between perceived depth and disparity was reversed both in the two line-contoured stereograms and in the random-dot stereogram in the middle of the wearing period, but the normal relation often returned late in the wearing period. When subjects observed two objects while wearing the spectacles and were asked which appeared the nearer, veridical depth perception increased as the wearing-time passed. These results indicate that the visual transformation reversing the direction of binocular disparity causes changes both in binocular stereopsis and in processes integrating different depth cues.
Apparent Minification in an Imaging Display under Reduced Viewing Conditions
Authors: Meehan James W
Published: January 2007

When extended outdoor scenes are imaged with magnification of 1 in optical, electronic, or computer-generated displays, scene features appear smaller and farther than in direct view. This has been shown to occur in various periscopic and camera-viewfinder displays outdoors in daylight. In four experiments it was found that apparent minification of the size of a planar object at a distance of 3–9 m indoors occurs in the viewfinder display of an SLR camera both in good light and in darkness with only the luminous object visible. The effect is robust and survives changes in the relationship between object luminance in the display and in direct view and occurs in the dark when subjects have no prior knowledge of room dimensions, object size or object distance. The results of a fifth experiment suggest that the effect is an instance of reduced visual size constancy consequent on elimination of cues for size, which include those for distance.
Monocular and Dichoptic Interactions between Moving and Stationary Stimuli
Authors: Wade Nicholas J , Swanston Michael T
Published: January 2007

Visual motion of a physically stationary stimulus can be induced by the movement of adjacent stimuli. The frequencies of motion reports and the angular separations required to induce motion were determined for a number of stimulus configurations. A stationary stimulus was fixated in the centre of the display and the point at which induced motion was initially reported was measured. In the first experiment either one or two stationary stimuli were presented in the centre of a display and either one or two similar stimuli moved horizontally towards them. The percentage of trials on which motion was induced varied with the display configuration, being greatest with two moving and one stationary stimuli. The angular separations at which motion was reported were about 2 deg for all conditions. In the second experiment the binocular interaction of such induced motion was examined. A single static fixation stimulus was presented binocularly and a range of monocular or dichoptic conditions was examined: a single moving stimulus to one eye, two moving stimuli to one eye, or two moving stimuli dichoptically. Induced motion was reported on about 90% of the trials for the monocular and dichoptic conditions with two moving stimuli. Motion was first induced at similar angular separations by two moving stimuli, whether presented monocularly or dichoptically. Binocular interaction was further examined with a display that induced motion in the stimulus presented to one eye but not in that presented to the other: this resulted in the apparent motion in depth of the binocularly fixated stimulus.
Visual Recognition of Mother by Young Infants: Facilitation by Speech
Authors: Burnham Denis
Published: January 2007

Infants recognise their mother's voice at birth but appear not to recognise visual-only presentations of her face until around 3 months. In a series of experiments visual discrimination by infants aged 1, 3, and 5 months of their mother's and a female stranger's face was investigated in visual-only and visual-plus-speech conditions. In the first experiment these infants' discrimination of mother's and female stranger's faces was measured by their visual-fixation-preference scores. Discrimination was found to be facilitated by the addition of speech information. In experiment 2 naive adults viewed silent videotapes of infants from experiment 1 and judged whether the mother had been presented on the infants' left or right. This added further information to the fixation-preference results of experiment 1: it was found that 1-month-olds discriminate mother's and stranger's face only in the presence of speech information, whereas 3-month-olds also do so in visual-only conditions. In experiments 3 and 4 the relative salience of lip movements and voice information in visual recognition of mother's face was investigated. In experiment 3, no significant differences in infants' visual-fixation-preference scores were obtained. However, in experiment 4 adults' ‘where is mother?’ judgments of videotapes from experiment 3 were found to be more accurate in the voice than in the lip-movements conditions, especially for the 3-month-olds and more accurate when mother rather than stranger was talking. It is concluded that young infants' visual recognition of mother is facilitated by addition of speech information, that it is primarily the voice component of speech that causes this facilitation, and that social discrimination is best indexed by a dependent variable which is sensitive to a range of facial cues provided by infants.
Interaction of Visual and Tactile Information in the Control of Chicks' Locomotion in the Visual Cliff
Authors: Green Patrick R , Davies Ian B , Davies Mark N O
Published: January 2007

The behaviour of two-day-old chicks placed on the deep side of a visual cliff was examined. With increasing depth of the floor below the chicks, latency to move over the deep side towards another chick on the shallow side increased, while speed of locomotion decreased. Chicks given the same incentive to step over a visible edge onto the deep side showed a stronger inhibition of movement at all depths, indicating that absolute depth of a surface and relative depth of an edge affect behaviour differently. At depths greater than 4 cm, the majority of chicks performed a jump from the deep to the shallow side, and the distances over which they jumped corresponded to those jumped when tested with a real gap. These results suggest that detection of the far side of a gap alone is sufficient to elicit a jump. Just before jumping, chicks adopted a head orientation which depended on the vertical distance of the cliff edge below them. Changes in head orientation did not maintain retinal fixation of the edge, and may instead be important in setting the correct direction of thrust when jumping.
Perceptual Frames of Reference and Two-Dimensional Shape Recognition: Further Examination of Internal Axes
Authors: Quinlan Philip T , Humphreys Glyn W
Published: January 2007

Three experiments on the perception of simple four-sided two-dimensional shapes are reported. In the first experiment subjects were given a paper-and-pencil test in which they had to consider each of a set of shapes in turn. They were instructed to draw in what they considered to be the most salient axis of each of the shapes ie a line that they felt most naturally went with the shape. The results showed a significant tendency to draw an axis of symmetry if one was present. However, when presented with instances of a shape that was elongated but possessed no symmetries they failed to consistently draw any particular axis. A further, speeded classification, task revealed that for this shape explicit axis information appeared not to influence performance. In contrast, such information clearly affected performance with a shape that did possess a salient axis of symmetry and elongation. Indeed this axis was shown to be integral with the contour of the shape when a final classification experiment was carried out. The axis of elongation of the other shape acted as a characteristic which was separable from the contour. The results are discussed in relation to accounts of shape perception which assume that a necessary stage in the perception of shape is the derivation of an axis-based structural description.
Asymmetrical Effect of Crossed and Uncrossed Disparity on Stereoscopic Capture
Authors: Ishigushi Akira , Wolfe Jeremy M
Published: January 2007

When a real or subjective contour is superimposed on a repetitive texture or ‘wallpaper pattern’, the apparent depth of the elements of the wallpaper pattern may be influenced by the contour. When the contour has crossed disparity, the elements inside the contour are seen floating in the plane of the contour. This is called ‘stereoscopic capture’. On the other hand, when the contour has uncrossed disparity a different, somewhat unstable, percept is seen. The wallpaper elements are either seen to form a transparent surface floating in front of the contour, or all of the elements inside and outside of the contour are seen to lie in the uncrossed plane of the inducing contour. We suggest that the asymmetry between crossed and uncrossed stereo capture is a by-product of the different roles played by crossed and uncrossed disparity in stereoscopic surface construction: specifically, crossed and, perhaps, zero disparity spreads one-directionally into a figure from a contour whereas uncrossed disparity spreads out from a figure in all directions. These points are illustrated with a series of demonstrations.
Inferring Structure from Motion in Two-View and Multiview Displays
Authors: Liter Jeffrey C , Braunstein Myron L , Hoffman Donald D
Published: January 2007

Five experiments were conducted to examine constraints used to interpret structure-from-motion displays. Theoretically, two orthographic views of four or more points in rigid motion yield a one-parameter family of rigid three-dimensional (3-D) interpretations. Additional views yield a unique rigid interpretation. Subjects viewed two-view and thirty-view displays of five-point objects in apparent motion. The subjects selected the best 3-D interpretation from a set of 89 compatible alternatives (experiments 1–3) or judged depth directly (experiment 4). In both cases the judged depth increased when relative image motion increased, even when the increased motion was due to increased simulation rotation. Subjects also judged rotation to be greater when either simulated depth or simulated rotation increased (experiment 4). The results are consistent with a heuristic analysis in which perceived depth is determined by relative motion.
Convergence Responses to Monocularly Viewed Objects: Implications for Distance Perception
Authors: Predebon John
Published: January 2007

In four experiments the role of dark vergence and the implied distance from the familiar-size and suggested-size cues to distance on the convergence response was investigated. A nonius-alignment technique was used to measure the convergence response in total darkness (dark vergence) and the fusion-free convergence response to monocularly viewed objects presented at a distance of 75 cm under otherwise reduced stimulus conditions. Observers also estimated the size and distance of the objects. The results indicated a significant association between individuals' dark-vergence distances and the convergence distances to the objects. Furthermore, the convergence response was influenced by the implied distance from the familiar-size cue but not by the implied distance from size suggestions. Both the familiar-size and the suggested-size cues influenced reports of distance. The implications of these findings for distance perception are discussed with particular reference to the familiar-size cue to distance.
A Computational Examination of Image Segmentation and the Initial Stages of Human Vision
Authors: Watt Roger
Published: January 2007

A novel approach to the question of image segmentation is considered. Instead of relying on edge-detection mechanisms to encircle the image of an object, it is proposed that the general Gestalt-like properties of images of objects can be used. These manifest themselves as particularly simple properties at relatively coarse spatial scales when the image is filtered with orientation-selective filters. The first part of the paper is concerned with a computational analysis of this proposal. A key issue is the question of how the information in filtered images is extracted. A simple primitive parametric description of zero-bounded blobs is used in this paper. It is shown how such a scheme can support readily the clustering of features with Gestalt-like properties. In the second part of the paper, two general difficulties for vision that are particularly severe for the present scheme are considered. The first of these are the effects of strongly asymmetric illumination. The second are the effects of using a cluttered scene. In each case the nature of the problem is examined and the nature of the computational solution considered.
Do Young Children Reverse Ambiguous Figures?
Authors: Rock Irvin , Gopnik Alison , Hall Susannah
Published: January 2007

Most adult observers tend not to reverse ambiguous figures if they are not informed about the ambiguity of the figure. The question was asked whether very young children who have rarely, if ever, seen any kinds of ambiguous figures will reverse if uninformed, and also how they will behave if they are informed. It was found that 3 and 4 year olds never reverse when presented with two different kinds of ambiguous figures when uninformed, and only some do even when informed; further, those that do reverse do so only once or twice over a 60 s inspection period. These results are interpreted as further confirmation of an earlier finding with adults—that reversal is not simply a matter of prolonged inspection of an ambiguous figure leading automatically to neural satiation. Instead, cognitive factors such as utilization of memory and intention are implicated.
On the Contribution of a Binocular ‘AND’ Channel at Contrast Threshold
Authors: Wilcox Laurie M , Timney Brian , Girash Michele
Published: January 2007

Three experiments are reported in which an attempt was made to isolate the contribution of an AND channel by measuring aftereffects following alternating monocular adaptation. The first two were designed to test Wolf and Held's proposal that the binocular AND channel does not respond at contrast threshold. In the first experiment the relative sizes of monocular and binocular contrast threshold elevation were compared with the pattern of aftereffects obtained in a study of the suprathreshold tilt aftereffect. Identical patterns of results were obtained under the two adaptation conditions. In the second experiment, the monocular and binocular contrast-reduction aftereffect reported by Blakemore et al was measured over a wide range of reference contrasts. As in the previous experiment, the monocular effect was greater than the binocular effect. This occurred at all reference contrasts. These data support the conclusion that the AND channel contributes to visual performance in the same manner, irrespective of stimulus contrast. In the final experiment an alternative explanation for existing evidence against the existence of an AND channel was assessed.
Factors Limiting Large-Scale Localisation
Authors: Sterken Yvonne , Toet Alexander , Yap Yen-Lee
Published: January 2007

The mechanisms mediating relative spatial localisation in the visual system are still unclear. There is a growing amount of evidence that this capability is not merely limited by the processing of the front-end visual system. Models of localisation should, therefore, include higher-level processing stages. A careful study of the sources of error in localisation tasks may further our understanding of the nature of these processes.

A study is reported in which the possible role of higher-order processing in relative spatial localisation is explicitly addressed. For this purpose the error sources of threshold performance were investigated for two similar relative-spatial-localisation tasks: two-dot separation discrimination and two-dot orientation discrimination. Fovea-centred stimuli with large dot separations were used. The front-end processing for these stimuli is probably identical in both tasks. Hence, differential effects of the variation of the experimental parameters on threshold performance for both tasks may reveal the characteristics of the higher-level processing involved.

The effects of dot separation, stimulus orientation, and experimental procedure (single-stimulus binary forced choice versus two-alternative forced choice) on threshold performance for both tasks are reported. The results show that thresholds for both tasks increase proportionally with dot separation. However, separation-discrimination thresholds are always significantly higher than orientation-discrimination thresholds. Thresholds for separation discrimination are independent of stimulus orientation. In contrast, orientation-discrimination thresholds show an oblique effect: thresholds are consistently lower for horizontal stimuli. Both tasks also show a different dependency of threshold behaviour on the experimental procedure. For a horizontal stimulus orientation, separation discrimination is better with an explicit (physical) reference standard, whereas orientation discrimination is better with an implicit referent.

These differential effects cannot be explained by any of the known characteristics of the front-end visual system. They suggest that large-scale spatial-localisation performance is probably limited at a processing level at which spatial relations are explicitly represented.
Vection: The Contributions of Absolute and Relative Visual Motion
Authors: Howard Ian P , Howard Antonie
Published: January 2007

Inspection of a visual scene rotating about the vertical body axis induces a compelling sense of self rotation, or circular vection. Circular vection is suppressed by stationary objects seen beyond the moving display but not by stationary objects in the foreground. We hypothesised that stationary objects in the foreground facilitate vection because they introduce a relative-motion signal into what would otherwise be an absolute-motion signal. Vection latency and magnitude were measured with a full-field moving display and with stationary objects of various sizes and at various positions in the visual field. The results confirmed the hypothesis. Vection latency was longer when there were no stationary objects in view than when stationary objects were in view. The effect of stationary objects was particularly evident at low stimulus velocities. At low velocities a small stationary point significantly increased vection magnitude in spite of the fact that, at higher stimulus velocities and with other stationary objects in view, fixation on a stationary point, if anything, reduced vection. Changing the position of the stationary objects in the field of view did not affect vection latencies or magnitudes.
Pseudophakes Experience Apparent Minification in an Imaging Display
Authors: Meehan James W , Smith George , Day Ross H
Published: January 2007

Apparent minification of virtual images has been attributed to accommodation micropsia, that is, a reduction in the apparent size of viewed objects accompanying an inward accommodation of the eyes. Thirteen bilateral pseudophakes incapable of accommodation but with good residual vision were tested monocularly for apparent minification in the viewfinder of a single-lens reflex camera. Apparent minification of about the same order as that typically found with normals occurred with the pseudophakic observers, demonstrating that pseudophakes are subject to distortions in apparent size with virtual-imaging displays in the same way as normals, thus establishing that visual accommodation is not a necessary condition for the effect.
A Model for Identifying the Perceptual Centre of Polygons
Authors: Davi Marco
Published: January 2007

An attempt is made to develop a general model of perceptual-centre determination. The model describes the possible ‘perceptual operations’ involved in determining the perceptual centre of flat figures. The specific steps in the model are: (i) determining the orientation and size of the figure; (ii) determining the ‘base’ of the figure and its ‘top—bottom axis’. It is suggested that anisotropy along the main axes of the figures determines a displacement of the perceptual centre toward the phenomenal top of the shape. A quantitative measure for the displacement of the perceptual centre from the area barycentre of the figure is introduced.
Water-Level Representation by Men and Women as a Function of Rod-And-Frame Test Proficiency and Visual and Postural Information
Authors: Robert Michèle , Ohlmann Théophile
Published: January 2007

In the water-level task, it has been repeatedly shown that, compared with men, women more often fail to represent the surface of a liquid as horizontal regardless of the tilt of the container. An attempt was made to reduce this robust gender gap through the manipulation of relevant upright references conveyed both by the position of the stimuli and the posture of the subject. It was reasoned that bringing the women to focus on such gravitational references through postural adjustment might help their performance equal that of men, thus shedding some light on the nature of the difficulty they experience in the standard setting. A lesser effect was anticipated among men. However, the results showed that, even after controlling for proficiency in the correlated visuospatial situation of the rod-and-frame test, the performance of men always surpassed that of women. Irrespective of gender, water-level representation on vertical sheets was unaffected by the subject's posture, whereas it improved when horizontal sheets were coupled with the most unstable posture. Whereas the persistence of the yet-unaccounted-for gender difference was underscored, the contributions of visual and postural cues issued at arm and full-body levels were discussed.
Modality-Specific Differences in the Processing of Spatially, Temporally, and Spatiotemporally Distributed Information
Authors: Mahar Doug , Mackenzie Brian , McNicol Don
Published: January 2007

The extent to which auditory, tactile, and visual perceptual representations are similar, particularly when dealing with speech and speech-like stimuli, was investigated. It was found that comparisons between auditory and tactile patterns were easier to perform than were similar comparisons between auditory and visual stimuli. This was true across a variety of styles of tactile and visual display, and was not due to limitations in the discriminability of the visual displays. The findings suggest that auditory and tactile representations of stimuli are more alike than are auditory and visual ones. It was also found that touch and vision differ in terms of the style of information distribution which they process most efficiently. Touch dealt with patterns best when the pattern was characterised by changes across time, whereas vision did best when spatially or spatiotemporally distributed patterns were presented. As the sense of hearing also seems to specialise in the processing of temporally ordered patterns, these results suggest one way in which the senses of hearing and touch differ from vision.
Temporal Properties of Colour and Shape Priming: Evidence of Multiple Components of Attention
Authors: Laarni Jari , Häkkinen Jukka
Published: January 2007

It has been shown in several studies that the selection of letters or numerals from an array can occur efficiently if criteria such as location, colour, shape, or size are used. It is also known that there are at least two components of spatial attention, the transient exogenous and the sustained endogenous. An interesting question is whether it is possible to elicit similar components when colour or shape information is used as a selection criterion. Experiments are reported the aim of which was to try to produce colour or shape precue effects on location and colour/shape discrimination accuracy, and to determine the minimum latency of these effects by sampling numerous cue lead times from 0 ms to 1000 ms. The results showed that, although accuracy did not increase monotonically with increased cue lead time, there were two transient peaks of performance at cue lead times of 0–200 ms, culminating at 30–50 ms and at 160–200 ms. It is suggested that the first component reflects nonspecific exogenous activation, triggered by the onset of a cue; the second component, in turn, may reflect feature-specific endogenous activation related to selection by colour or shape.
The Dependence of Two-Dimensional Shape Perception on Orientation
Authors: Rock Irvin , Schreiber Charles , Ro Tony
Published: January 2007

While it is true that in daily life we generally recognize objects regardless of their orientation, previous experiments involving novel shapes indicate a decline in recognition when these are tested in altered orientation. Here the question is raised of whether there is a component of shape perception based purely on the geometry of an object, independent of orientation. By means of two tests designed to eliminate awareness of change of orientation, one more stringent than used heretofore, it was found that shape perception is dependent on orientation. The apparent contradiction between these findings and the apparent orientation-free character of recognition in daily life is discussed.
Infants Perceive Spatial Structure Specified by Line Junctions
Authors: Yonas Albert , Arterberry Martha E
Published: January 2007

Lines in drawings can be perceived as the corners where surfaces intersect, outer boundaries of surfaces, or as markings on a surface. In this study infants' ability to distinguish between lines that indicate corners and edges and lines that indicate markings was investigated. Infants aged 7.5 months were habituated to line displays in which the lines specified a three-dimensional cube or two overlapping rectangles. Both displays contained lines indicating corners, edges, and surface markings. After habituation, infants viewed two test displays, one in which the corners or edges were deleted and one in which the surface markings were deleted. Infants looked significantly longer at the displays that lacked the corners or edges. The results suggest that infants attend to lines that depict corners and edges to a greater degree than they attend to lines that depict markings. Infants may do so because corners and edges specify the shapes of objects whereas markings do not.
Stereokinetic Effects with Sharp and Fuzzy Illusory Contours
Authors: Masini Roberto , Ferraro Mario , Costa Tommaso
Published: January 2007

A black, 8-shaped pattern, whose centre of gravity is in the centre of a rotating disc, appears to split into two black discs rotating with phenomenal independent motion, orientation stability, and sliding of one on the other. The type of observed movement, the order of overlapping, and the extent of the stereokinetic depth in relation to the contour type and different dimensions of the pattern were investigated. The experimental data show that a fuzzy contour facilitates the stereokinetic effect. Furthermore, the extent of the stereokinetic depth has been found to be greater in case of fuzzy contour and vertical orientation of the pattern. These results are in contrast with the models in which this effect is considered as a problem of minimisation of distances or velocities. A vector model of the observed movement and an interpretation of the overlapping based on an energy approach are proposed. A tentative explanation of the stereokinetic depth for our patterns is put forward.
Disparity Scaling and the Perception of Frontoparallel Surfaces
Authors: Rogers Brian J , Bradshaw Mark F
Published: January 2007

Binocular disparity can be defined in a variety of ways and its measurement depends upon the particular coordinate framework chosen. As a result of the inverse square law, binocular disparities need to be scaled by some estimate of absolute distance if they are to be interpreted correctly. The experiments described in this paper investigated the extent to which (i) the vergence angle and (ii) the horizontal gradient of vertical disparities or ‘differential perspective’ provide the necessary information for judging that a stereoscopic surface is flat and frontoparallel. For small displays (<20 deg) vergence is more effective than differential perspective in scaling frontoparallel surfaces but for larger displays (>30 deg), differential perspective plays the major role. When both cues together specify the viewing distance, the constancy of frontoparallel-surface scaling is close to perfect for all sizes of display up to 80 deg. Analysis of the geometry of stereoscopic images shows that when a surface patch lies in a frontal plane, the binocular horizontal size ratio of any surface feature is equal to the square of its binocular vertical size ratio, whatever its distance from the observer.
Cortical Representation of Visual Three-Dimensional Space
Authors: Trotter Yves
Published: January 2007

Perception of real depth includes information on stereopsis and distance. How both interact in the visual pathway was the subject of a study performed on the behaving monkey. Neurons in the primary visual cortex (area V1) have their activity, visual and/or spontaneous, modulated by the viewing distance. Disparity selectivity may be present or better expressed at a given viewing distance. This modulation is independent of the visual pattern. The use of prisms shows that vergence is implicated in this phenomenon. Consequently, extraretinal signals related to ocular motility have access to area V1. Among them, proprioceptive signals from the eye muscles have been shown to be involved in visual cortical function and in the development of depth perception. It is possible that the same signals may also be involved in the distance modulation shown in V1 neurons, but this remains to be examined. A possible specialisation of disparity-selective cells in different cortical areas is discussed.
Perceiving Heading in the Presence of Moving Objects
Authors: Warren William H , Saunders Jeffrey A
Published: January 2007

In most models of heading from optic flow a rigid environment is assumed, yet humans often navigate in the presence of independently moving objects. Simple spatial pooling of the flow field would yield systematic heading errors. Alternatively, moving objects could be segmented on the basis of relative motion, dynamic occlusion, or inconsistency with the global flow, and heading determined from the background flow. Displays simulated observer translation toward a frontal random-dot plane, with a 10 deg square moving independently in depth. The path of motion of the object was varied to create a secondary focus of expansion (FOE') 6 deg to the right or left of the actual heading point (FOE), which could bias the perceived heading. There was no effect when the FOE was visible, but when the object moved in front of it, perceived heading was biased toward the FOE' by ∼1.9° with a transparent object, and ∼3.4° with an opaque object. The results indicate that scene segmentation does not occur prior to heading estimation, which is consistent with spatial pooling weighted near the FOE. A simple template model based on large-field, center-weighted expansion units accounts for the data. This may actually represent an adaptive solution for navigation with respect to obstacles on the path ahead.
Cognitive Effects on Visually Induced Body Motion in Children
Authors: Lepecq Jean-Claude , Giannopulu Irini , Baudonniere Pierre-Marie
Published: January 2007

Cognitive effects on linear sagittal vection in children were investigated. Forty children (7 and 11 years old) were exposed to a bilateral backward optical flow in a single physical condition (seated in a stationary armchair) but in two contrasted cognitive conditions. In one cognitive condition, the children were precisely informed that the armchair could move. In the other, they were informed that the armchair could not move. In each age group, half the children were assigned to one cognitive condition, the other half to the other condition. The results indicate that knowledge about the plausibility of a physical displacement does not affect the probability of obtaining vection. However, at both ages, the latencies for reporting vection were shorter when the physical displacement was known to be possible than when it was known to be impossible. The present results indicate that exclusively cognitive factors do not affect vection occurrence but can modulate latencies for reporting vection.
The Microgenesis of Illusory Figures: Evidence for Visual Hypothesis Testing
Authors: Parks Theodore E
Published: January 2007

When a pattern that would usually produce an illusory figure was altered so as to include ‘contradictory evidence’ and was presented briefly, the frequency of that illusion first increased but then decreased with increased viewing time.
Texture Discrimination at the Cyclopean Retina
Authors: Pérez-Martínez Diana
Published: January 2007

One of the open questions within the study of texture discrimination is whether the underlying neural mechanisms are located within the two monocular pathways, or whether they are located at more central areas that process binocular information. This question is considered here in psychophysical experiments of texture discrimination involving stereograms. The results show that texture discrimination for differences in form and size occur after binocular fusion. Moreover, the suitability of random-dot stereograms versus line-figure stereograms for this research has been studied. It was found that discrimination for differences in form was better with line-figure stereograms whereas discrimination for differences in size was better with random-dot stereograms.
Evidence That Luminant and Equiluminant Motion Signals are Integrated by Directionally Selective Mechanisms
Authors: Heidenreich Susan M , Zimmerman G Lee
Published: January 2007

Three experiments tested whether motion information for nonequiluminant (luminant) and equiluminant dots affects direction judgments when both types of stimuli are moving simultaneously in the same display. The motion directions for the two sets of dots were manipulated to produce four direction differences (0°, 30°, 60°, and 90°). The equiluminant dots were moved in a perfectly correlated fashion, but the percentage of correlated motion for the luminant dots was varied. When subjects judged whether the directions of the equiluminant and luminant dots were the same or different, performance for the conditions with 0°, 60°, and 90° difference improved as the percentage of correlated luminant motion increased. The same result occurred for a control display that contained two sets of luminant dots. However, for the 30° difference, performance was at chance level for the control display, but dropped below chance for the equiluminant-luminant display. When subjects indicated just the direction of the luminant dots, judgments were not affected by equiluminant motion. Judgments for the equiluminant dots also were accurate, except for the conditions with 30° difference; these responses were biased by the luminant motion, indicating some form of motion capture. The interactive effects are discussed in terms of a directionally selective mechanism that combines equiluminant and luminant motion signals.