bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual Scan Patterns of Rhesus Monkeys Viewing Faces
Authors: Keating Caroline F , Keating E Gregory
Published: January 2007

Two rhesus monkeys viewed black/white photographic slides depicting rhesus, human, chimpanzee, and schematic faces with direct gazes. Eye-track apparatus was used to assign visual fixations to one of four facial regions: the two eyes, nose, or mouth. Results showed that the eyes of stimulus faces received a disproportionate number of fixations from both observers across all stimulus face types. Stimulus faces depicting rhesus and human facial gestures shifted scan patterns somewhat, but did not disrupt the preoccupation with eyes. When the features of schematic faces were rearranged into non-facelike configurations, fixations directed to schematic stimuli were typically reduced in number.
A Cross-Cultural Comparison of the Use of a Gestalt Perceptual Strategy
Authors: Perkins D N , Deregowski Jan B
Published: January 2007

The ability to discriminate whether pictured box shapes (parallelopipeds) are projections of three-dimensional rectangular forms has been demonstrated by Perkins and Cooper in US populations and interpreted as a symptom of a general Gestalt strategy in perception. Deregowski suggested earlier that this perceptual strategy might not appear as strongly in less ‘carpentered’ cultures, among perceivers less familiar with Western modes of depiction. A study is reported in which the performance on the discrimination by US children in grades 1, 4, and 7; and children from Zimbabwe, Africa, in grades 1, 2, 4, and 7—children of less experience with pictures and urban environments—has been examined. All groups evinced the discrimination at high levels of statistical significance. However, the findings disclosed much less accurate performance in the Zimbabwe groups at all grade levels, and no improvement with age either in the US or in Zimbabwe. The absence of improvement argues against an explanation of the difference between the US and Zimbabwe groups in terms of either a carpentered-world hypothesis or a difficulty with picture perception, at least when those interpretations are taken in their simplest forms.
A Demonstration of the Visual Importance and Flexibility of Spatial-Frequency Amplitude and Phase
Authors: Piotrowski Leon N , Campbell Fergus W
Published: January 2007

To establish how little information the human visual system requires for recognition, common objects were digitally manipulated in the Fourier domain. The results demonstrate that it is not only possible, but also quite efficient, for a (biological) visual system to exist with very few phase relationships among the component spatial frequencies of the (retinal) image. A visual example is then presented which illustrates how certain phase relationships can hinder, or completely eliminate, the recognition of visual scenes.
Visual Masking: A Unified Approach
Authors: Anbar Sybille , Anbar Dan
Published: January 2007

The suppression effect observed in masking is assumed to be due to neural inhibition between two stimuli that interact spatially or within a narrow span of time in the fashion demonstrated in simultaneous brightness-contrast experiments. Three principles are brought together in a comprehensive mathematical model of visual masking. The three principles are: lateral inhibition, the integrated visual response function (VRF), and stimulus decay after its offset over a limited period of time (up to about 100 ms). Block's law is extended to apply to the integration of the VRF, including decay. The three principles combined are sufficient to explain well-known masking phenomena such as metacontrast, and forward and backward masking. The mathematical model presented demonstrates clearly the common underlying basis of all masking. The validity of the lesser documented decay after stimulus offset, a necessary assumption to explain masking effects with stimuli that are delayed relative to each other, is demonstrated with experimental evidence.
The Oblique Effects of Pattern and Flicker Sensitivity: Implications for Mixed Physiological Input
Authors: Essock Edward A , Lehmkuhle Stephen
Published: January 2007

The inferior contrast sensitivity for oblique gratings has been previously demonstrated at high spatial frequencies with an absolute criterion. In this study contrast sensitivity at oblique and main axis orientations was obtained under separate pattern and flicker threshold criteria across a range of both spatial and temporal frequencies. The anisotropy of contrast sensitivity was not observed at low spatial frequencies under any stimulus or criterion conditions. At high spatial frequencies the anisotropy was observed for both pattern and flicker thresholds, although the flicker anisotropy was less pronounced. If, as previously suggested, this anisotropy is mediated by X cells, then these psychophysical findings suggest a mixed model in which both pattern and flicker systems receive input from both X and Y-cell pathways.
The Construction of a Plane from Pictorial Information
Authors: Rock Irvin , Wheeler Deborah , Shallo Josephine , Rotunda Joseph
Published: January 2007

Experiments are described which support the theory that the perception of a plane receding in depth is based on a process of construction. Displays were created which eliminated direct or higher-order stimulus information concerning the orientation of a plane, such as texture gradients or perspective. Instead, objects and the shadows they cast sufficed to suggest and support a depth interpretation. The perceived location of objects on this constructed plane affects size perception thereby providing evidence for a computational rather than a direct theory of constancy.
Direction-Specific Tilt Illusion: With and without Gaze Fixation
Authors: Carney Thom
Published: January 2007

The perceived orientation of a test grating is rotated from its veridical orientation if an annulus grating with a similar orientation is present. The magnitude of this misperception was measured and found to be greater when the two gratings moved in the same direction than when they moved in opposite directions. This demonstration of a direction-specific tilt illusion is similar to the previously demonstrated direction-specific tilt aftereffect—which is to be expected if similar mechanisms are responsible for both phenomena. If the tilt illusion is caused by lateral inhibition between orientation-selective units, then these findings indicate that such inhibition is principally between units with similar orientation and direction of motion selectivities.
Effect of Brightness on Perceived Distance as a Figure—Ground Phenomenon
Authors: Egusa Hiroyuki
Published: January 2007

Two experiments were performed to compare the effects of brightness on perceived distance in the situations in which a target appeared either as figure (experiment 1) or as ground (experiment 2). In experiment 1 the stimulus array consisted of two small homogeneous target regions and a homogeneous surrounding region common to both; in experiment 2 it consisted of two large homogeneous target regions and a textured surrounding region. Subjects were asked to indicate which of the two targets appeared nearer and to make a verbal judgment of perceived depth between them. The results showed that the target having the greater brightness contrast with the surround is apt to be judged nearer when the targets appear as figure, and farther when they appear as ground. These findings support Egusa's hypothesis that the effect of brightness on perceived distance can be attributed to figure—ground differentiation between the target region to be judged and its direct surround.
Correspondence Strength in Apparent Movement: Reply to Petersik Et Al
Authors: Ullman Shimon
Published: January 2007

Petersik et al suggest that similarity and related effects are the result of a tradeoff between the short-range and long-range processes; the main point of disagreement centers around the source of these effects and does not bear directly on the main issues discussed in the original paper.
Depth Perception of Surfaces in Pictures: Looking for Conventions of Depiction in Pandora's Box
Authors: Berbaum Kevin , Tharp David , Mroczek Kenneth
Published: January 2007

The perception of depth in monocularly viewed pictures has been investigated with the use of a binocular rangefinder developed by Gregory. Two experiments are reported which focus upon stimulus conditions that were identified by Haber as conventions for rendering depth in pictures. Several conclusions, which concern assumptions that must be made in interpreting pictures according to such conventions, are supported by the results. There is a default or assumed layout of background space. The interpretation of a point in a depiction depends upon the interpretation of neighboring points, so that interpretations of local features influence the interpretations of nearby ‘empty’ areas. In photographs, the magnitude of apparent depth depends upon the degree of discrepancy between the position of the illuminating source and the observer's supposed light-source position. Also in photographs, apparent depth increases as the contrast between highlights and attached shadows increases.
Is Target Movement as Well as Target Displacement a Stimulus for Saccadic Eye Movements?
Authors: Findlay John M , Zanuttini Lucia
Published: January 2007

The effects of visual movement on saccadic eye movement have been examined. In a classic apparent-movement demonstration with two successively exposed line-segment targets the quality of the movement is dependent on the relative orientation of the line segments. If saccadic eye movements are elicited between the targets in this situation, the configuration leading to optimal apparent movement also leads to the shortest-latency saccades. When a single line segment is succeeded by two line segments flanking it on opposite sides, and if one of these has the same orientation as the initial one and the other a different orientation, then apparent motion is seen between the two lines with the same orientation. However, the direction of saccades elicited in this configuration is not influenced by the relative orientations of the line segments. The two results together suggest that the effect of visual movement on saccadic eye movement is nonspecific.
A Refutation of the Hypothesis of the Superfidelity of Caricatures Relative to Photographs
Authors: Hagen Margaret A , Perkins David
Published: January 2007

The experiment was designed to test the hypothesis that caricatures, relative to photographs, are ‘superfaithful’ carriers of information for facial recognition. Subjects were shown fifteen pictures of people's faces and were then asked to pick those same people out of a set of fifty-four pictures. There were three sets of pictures: caricatures, profile-view photographs, and three-quarter-view photographs. There were nine groups of subjects: for three groups the exposure and test stimuli were in the same medium, for six groups the test stimuli were in one of the media not previously seen. Points were scored for the number of people correctly identified and the number of false positives. Facial recognition within medium was very good, but was seriously disrupted by any medium shift, especially those involving caricatures. It is argued that the superfidelity of caricature may be manifest only when the task involves recognition of actual persons rather than their pictures.
The Effect of Head Movements on Visual and Auditory Dominance
Authors: Easton Randolph D
Published: January 2007

Two experiments were performed to determine the effect of active auditory exploration (head movement) on visual and auditory dominance. In each experiment subjects located a small audio speaker unimodally or bimodally. On the bimodal trials a modality discordance was created by requiring prismatic viewing. Half the subjects in each experiment remained unaware of the discordance while the other half were informed that a prism was used, and its refracting properties were demonstrated. The second experiment differed from the first by allowing observers free head movement during target localization which was transduced and recorded electromechanically. The results indicated that knowledge of modality discordance greatly reduced visual bias of audition for observers with heads immobilized, but did not affect auditory bias of vision significantly. Observers permitted head movement but not provided with knowledge of discordance demonstrated visual bias which was substantially reduced from that found in the first experiment for no-knowledge subjects. Observers who were permitted head movement and provided with knowledge of discordance demonstrated no visual bias or auditory bias. Head movements were executed systematically, when permitted, and resulted in an increase in the precision of auditory localizations and a reduction in the biasing effect of vision. In contrast, head movement did not affect the precision of visual localizations. Results are discussed in terms of current hypotheses regarding perceptual dominance.
Effects of Brightness, Hue, and Saturation on Perceived Depth between Adjacent Regions in the Visual Field
Authors: Egusa Hiroyuki
Published: January 2007

The effects of brightness, hue, and saturation on perceived depth between adjacent regions have been examined. The stimulus consisted of two hemifields of different colors, and the subject was asked to state which appeared nearer and to judge the perceived depth between them. When both hemifields were achromatic, the perceived depth was found to increase with increasing brightness difference. Some subjects tended to judge the brighter side nearer, others the darker side nearer. With the achromatic–chromatic combination, there were no differences in perceived depth among three hue conditions, whilst with the chromatic–chromatic combination the perceived depth depended on hue combination. In terms of decreasing frequency of ‘nearer’ judgments the hue order was red, green, blue. When the two hemifields differed only in saturation, the perceived depth increased with increasing saturation difference, and whether the more saturated or the less saturated side was judged nearer depended on hue. It is argued that the effects of brightness and saturation on perceived distance from the observer can be attributed to figure–ground differentiation between adjacent regions in the visual field; but this argument does not cover the effect of hue under achromatic background conditions.
Depth Perception in Pandora's Box and Size Illusion: Evolution with Age
Authors: Chevrier Jacques , Delorme André
Published: January 2007

The aim of the experiment was to study the evolution with age (6, 8, 11 and 14 years) of pictorial depth perception in Pandora's box and to compare it with the evolution of size illusion with the same subjects and the same pictorial backgrounds. In addition to familiar size and relative position, each pictorial stimulus contained one or more of the following depth cues: linear perspective, texture gradient, and interposition. The two kinds of measurements produced different results. Size illusions, although present, did not vary with age but increased with the number of cues. Estimates of distance in Pandora's box increased with age and varied according to the type of cue present: texture gradient seemed to be critical to the amount of depth perceived. The correlation between size adjustments and distance adjustments was significant only for the two oldest groups of subjects (11 and 14 years).
Wobble Cones and Wobble Holes: The Stereokinetic Effect Revisited
Authors: Wilson John A , Robinson James O , Piggins David J
Published: January 2007

It is well-known that patterns of eccentric circles when slowly rotated give rise to compelling three-dimensional impressions of cones or conical holes which can ‘wobble’ as the pattern rotates. The wobble can be considered as part of the overall phenomenon of depth elicited from a rotating display, the ‘stereokinetic’ effect (SKE). This paper considers the three-dimensional appearance as being the result of the sliding of contours and thus it imitates the motion parallax found in real three-dimensional objects in motion. New variants of SK figures are used to examine these points. An analogy with computer programs is proposed which questions earlier views on the location of perceptual invariance.
Mental Rotation: A Computationally Plausible Account of Transformation through Intermediate Steps
Authors: Morgan Michael J
Published: January 2007

A critical difficulty in theories of the ‘mental rotation’ phenomenon has been to find a computationally plausible reason why the rotation should occur in small intermediate steps. It is pointed out that this difficulty is peculiar to metrical representations: if spatial relations are presented symbolically but nonmetrically, then the iterative or recursive application of minimal transformations is memory saving. A program rotter is described to illustrate this principle.
‘Peak Preference’ and Waveform Perception
Authors: Chadwick Peter K
Published: January 2007

Because the perception of waveforms has been relatively neglected in vision research, one phenomenon of waveform perception, the parsing of waves into peak-shaped rather than trough-shaped segments, is examined. It is suggested that this so-called ‘peak preference’ is a grouping rule which can determine figure—background segregation in some circumstances. It appears to resist explanation in terms of the spatial-filtering properties of the visual system. For a complete explanation of peak preference, the ecological significance for actions that wave stimuli would normally have in the natural setting has to be considered.
The Effect of Two-Dimensional and Three-Dimensional Distance on Apparent Motion
Authors: Mutch Kathleen , Smith Isabel M , Yonas Albert
Published: January 2007

The problem of how the visual system matches corresponding inputs from one instant to the next to produce the perception of motion has been experimentally examined. The specific concern was whether this correspondence problem is solved prior to the interpretation of three-dimensional distance. Observers judged the degree of apparent motion between pairs of lights in a conflicting motion display. Spatial separation of the lights was varied in two and three dimensions in order to assess whether retinal distance, actual depth, or some combination of these provided critical information for correspondence. The results support Ullman's contention that only two-dimensional (retinal) distances are used in establishing correspondence in motion perception.
An Investigation into the Representations Involved in Visual Masking
Authors: Forster Peter M
Published: January 2007

Two experiments are reported in which the nature of the representations involved in visual masking with spatially overlapping stimuli is investigated. Recent work is described which was consistent with the proposal of Breitmeyer and Ganz (1976) that masking phenomena can be understood in terms of interactions between spatial-frequency-tuned channels. In the first experiment targets which had been filtered to contain only high or low spatial frequencies were masked by high or low frequency masks. The results were more consistent with a model of masking in which higher-order representations, possibly derived from spatial-frequency information, were involved. A second experiment was carried out to test this conjecture which involved investigating the interaction between the effects of learning and the type of information used in target identification. The results provided further support for the model.
Magnitude Estimates of Cold Pressor Pain: Effects of Suggestions, Cognitive Strategy, and Tolerance
Authors: Spanos Nicholas P , Jones Bill , Brown Jude M , Horner Donna
Published: January 2007

Pain magnitude when subjects immersed an arm in ice water was assessed by means of a magnitude estimation procedure during baseline and posttest sessions. Before the posttest session, subjects either received or did not receive an analgesic suggestion. Best-fit functions were linear, though power fits were also good. Analgesic suggestions had no effect on the rate of change in pain intensity. When subjects were classified as copers or catastrophizers on the basis of written testimony, pain intensity increased more rapidly for catastrophizers than for copers during the posttest session but not during the baseline session. Subjects who kept their arm immersed for more than 240 s were classified as high in tolerance. High-tolerance subjects experienced a slower rate of growth in pain intensity than low-tolerance subjects. Theoretical implications of the results are discussed.
Low Spatial Frequencies Dominate Apparent Motion
Authors: Ramachandran Vilayanur S , Ginsburg Arthur P , Anstis Stuart M
Published: January 2007

Experiments are reported which have been designed to establish what features of a pair of figures can be used as an input for apparent motion. The display consisted of a central figure, A, which appeared briefly and was followed immediately afterwards by two figures, B and C, which appeared on either side of the original location of A. Figure A can thus move towards either B or C. When A was a low-pass filtered square it moved towards C (a low-pass filtered square that was similar to A but ‘rotated’ by 45°) rather than towards B (a high-pass filtered square identical to A in orientation and size). When A was an unfiltered square it moved towards C (a low-pass filtered square of identical orientation) rather than towards B (a high-pass filtered square of identical orientation). Lastly, when A was a ‘solid’ square it moved towards C (a solid circle) rather than towards B (an outline square). All three experiments suggest that the direction of perceived movement is determined exclusively by low spatial frequencies rather than by similarity of oriented edges, especially when speed of alternation is rapid.
Apparent Movement Induced by Afterimages
Authors: Power Roderick P
Published: January 2007

A small light source viewed in the dark through an afterimage produced by an electronic flash may appear to move along short random paths. Experiment 1 shows that this is not an instance of the autokinetic phenomenon, and experiment 2 shows that it is not related to the ‘fluttering hearts' phenomenon. On the basis of experiments 1 and 3 it is concluded that small-scale ocular drifts, microsaccades, and possibly tremors cause the whole afterimage to move. The afterimage serves as a frame of reference and induces movement of the light source.
Visual, Kinaesthetic and Cross-Modal Development: Relationships to Motor Skill Development
Authors: Hulme Charles , Smart Anne , Moran Georgina , Raine Adrian
Published: January 2007

The ability of children between the ages of 5 and 10 years to match the length of lines within and between the modalities of vision and kinaesthesis was studied. No evidence was found for specific increases in cross-modal skill which could not be explained in terms of within-modal development. Performance in the perceptual task was related to measures of developing motor skill in the children. Substantial relationships were found between performance on the within-modal tasks and motor skill, but no significant relationships were found between cross-modal measures and motor skill development. It is concluded that the development of cross-modal integration is not a major determinant of motor skill development.
The Cylinder Configuration: When is a Distortion an Illusion?
Authors: Treisman Michel
Published: January 2007

A figure with one end rounded and the other concluding in an ellipse (the ‘cylinder configuration’) may appear longer than a rectangle of the same true length. It is proposed that when this configuration is processed as a three-dimensional body, it provides a cue for object orientation which causes the perceptual system to make an adjustment in the direction appropriate for maintaining size constancy. This effect may be considered a normal perceptual adjustment, appropriately applied. When the cylinder configuration is embedded in a context which does not favour its being processed as three-dimensional, a weaker adjustment in length may still occur. It is suggested that this effect, which may properly be classified as an illusion, may arise through direct association of the critical pattern of lines with the process of lengthening produced by the size-constancy mechanisms. Some relations of the present configuration to the Müller-Lyer illusion, and implications for the latter, are also discussed.
The Spatial Characteristics of Tactile Form Perception
Authors: Oldfield Simon R , Phillips John R
Published: January 2007

The perceived orientation of a raised letterform indenting the skin of the finger reverses (from normal to its mirror-image) when the letter is held in contact with the finger and both are rotated through 180° about the axis of the finger. Thus, though the pattern of stimulated skin receptors remains constant, the perceived orientation of the letter reverses. On the basis of this observation it is proposed that tactual perception of object form involves assignment of a spatial coordinate system within which the patterns of skin stimulation are interpreted. In experiments in which the orientations of letters and subjects are systematically varied within the environment, the occurrence or nonoccurrence of reversal in perceived orientation of letters has been used to investigate the origin of the proposed spatial coordinate system; that is, whether it is assigned with respect to the observer (egocentrically) or with respect to the environment (geocentrically). The results indicate that the assignment of coordinates is determined by both egocentric and geocentric factors. It is proposed that the reversal phenomena observed in these experiments, and in experiments of others which involve drawing characters on the skin, are consistent with Gibson's proposal that it is object form which is directly perceived, but that this involves interpretation of the patterns of skin stimulation within a framework of spatial coordinates.
The Effects of Temporal Modulation on the Perceived Spatial Structure of Sine-Wave Gratings
Authors: Parker Andrew
Published: January 2007

Evidence is presented that two distinct effects are generated when a sine-wave grating is temporally modulated. These effects may differentiated on the grounds of different responses with different forms of temporal modulation (drift or phase reversal), different behaviour with changes of visual eccentricity and with changes of contrast. One effect is roughly equivalent to spatial-frequency doubling, as described by Kelly. The other is seen as a fractional increase in apparent spatial frequency ie 1.2 × or 1.4 × the original. Earlier papers are reviewed to lend support to these conclusions.

The results obtained for spatial-frequency doubling are consistent with Kelly's model of a nonlinearity followed by a temporal integration. Spatial-frequency doubling emerges under conditions where a fractional increase in apparent spatial frequency would generally be expected but the particular spatiotemporal conditions are such that a breakdown in the motion-correspondence process may be suspected. Reasons for the existence of fractional shifts are not entirely clear, but it is argued that the similarity of the shifts induced by various manipulations (decreases of luminance, decreases of contrast, temporal modulation) are such that a general explanation must be sought, rather than one specific to temporal modulation alone.
On the Number of Intensity Levels Discriminated in Textures
Authors: Caelli Terry , Hübner Martin
Published: January 2007

The number of intensity levels detected in briefly displayed textures was studied as a function of two related spatial parameters: granularity and spatial frequency. A texture-discrimination paradigm was used to determine the discriminability of an original texture and of a version of it reduced (further ‘quantized’) in intensity levels over a range of texture granularities and frequency bandwidths. Results show specific sensitivities to intensity level reductions as a function of the spatial-frequency composition of the textures, with particular loss of sensitivity in the higher spatial-frequency regions.
Errors towards the Perpendicular in Children's Copies of Angular Figures: A Test of the Bisection Interpretation
Authors: Bremner J Gavin
Published: January 2007

Children distort angular figures so that the constituent angles are nearer 90° than they should be. This could be due to a perpendicular bias or a bisection bias, or to both. A study is reported which was designed to establish whether a perpendicular bias would appear independently of bisection. Twenty four-year-old children were tested on two types of angular figure: (i) a baseline with another line joining at the end at 45°, 90°, or 135° and (ii) a baseline with another line joining at the middle at 45° or 90°. Perpendicular errors were obtained both for ‘end’ and for ‘middle’ figures, but overall more strongly for ‘middle’ figures. However, while 90° ‘middle’ figures were copied more accurately than 45°/135° figures, this effect was only obtained for vertical and horizontal presentations of ‘end’ figures, and was reversed for oblique presentations. Also, for ‘end’ figures, directional errors varied with subtended-line orientation, whereas for ‘middle’ figures they varied with baseline orientation. It is concluded that although errors towards the perpendicular do occur with single-angle figures, angle equalisation may take place when there are two adjacent angles in the figure. One interpretation of the differing orientation effects is that in ‘middle’ figures strong internal relational forces produce a distortion that varies with the angle at which the figure is viewed, whereas in ‘end’ figures the absence of relational forces within the figure leads to a stronger influence from external cues.
Information about Three-Dimensional Shape and Direction of Illumination in a Square-Wave Grating
Authors: Bergström Sten Sture , Gustafsson Karl-Arne , Putaansuu Jorma
Published: January 2007

A homogeneous grey picture and a ‘Mondrian’ type of picture were illuminated by a projector with square-wave gratings of thirty different contrast values used as slides. Ten observers reported whether the picture appeared three-dimensional (3-D) (pleated) or flat. 3-D responses in this situation indicate colour constancy ‘at the cost of’ nonveridical depth perception.

The frequencies of 3-D responses were significantly higher for the structured picture than for the homogeneous grey one. In reports of the direction from which the apparent 3-D object appeared to be illuminated there was a significant preference for responses “from above” when the grating was horizontally oriented. With vertical orientation there was no preference for “from the left” or “from the right”.

The results from the first experiment contradict traditional cue theories of depth perception since the projection of the borders between the fields of the structured picture was invariant and expected to inform about the flatness of the picture. They are, however, in line with a model for perceptual analysis of reflected light into common and relative components proposed earlier by Bergström.

The difference in perceived direction of illumination between horizontally and vertically orientated gratings is discussed in connection with human ecology.
Maximizing Rigidity: The Incremental Recovery of 3-D Structure from Rigid and Nonrigid Motion
Authors: Ullman Shimon
Published: January 2007

The human visual system can extract 3-D shape information of unfamiliar moving objects from their projected transformations. Computational studies of this capacity have established that 3-D shape can be extracted correctly from a brief presentation, provided the moving objects are rigid. The human visual system requires a longer temporal extension, but it can cope with considerable deviations from rigidity. It is shown how the 3-D structure of rigid as well as nonrigid objects can be recovered by maintaining an internal model of the viewed object and modifying it at each instant by the minimal nonrigid change that is sufficient to account for the observed transformation. The results of applying this incremental rigidity scheme to rigid and nonrigid objects in motion are described and compared with human perception.
Spatiotemporal Continuity and the Perception of Causality in Infants
Authors: Leslie Alan M
Published: January 2007

Infant perception of a Michottean launching event in which one object causes another to move through collision is examined in a series of habituation-test experiments. A number of hypotheses concerning how infants aged around 30 weeks might perceive and encode launching and its noncausal variants are identified and tested. The results of the first experiment indicate that infants can perceive direct launching as an event with internal structure, that is, as composed of two temporally ordered movements. The nature of the encoding by the infants is perceptual and not specifically motor-based. The second experiment makes it seem unlikely that the infants encode independent spatial and temporal features (for example, contact and successivity), while the third experiment suggests a spatiotemporal continuity gradient. Some implications for the origins of causality are discussed.
What Does the Occluding Contour Tell Us about Solid Shape?
Authors: Koenderink Jan J
Published: January 2007

A new theorem is discussed that relates the apparent curvature of the occluding contour of a visual shape to the intrinsic curvature of the surface and the radial curvature. This theorem allows the formulation of general laws for the apparent curvature, independent of viewing distance and regardless of the fact that the rim (the boundary between the visible and invisible parts of the object) is a general, thus twisted, space curve. Consequently convexities, concavities, or inflextions of contours in the retinal image allow the observer to draw inferences about local surface geometry with certainty. These results appear to be counterintuitive, witness to the treatment of the problem by recent authors. It is demonstrated how well-known examples, used to show how concavities and convexities of the contour have no obvious relation to solid shape, are actually good illustrations of the fact that convexities are due to local ovoid shapes, concavities to local saddle shapes.
On the Perception of Glass Patterns
Authors: Prazdny Kvetoslav
Published: January 2007

Recent findings about our perception of Glass patterns suggest that the processes responsible for the perception of a global pattern composed of random features may be mechanisms performing measurements in the spatial and energy domain rather than logical operations on symbolic descriptions. These mechanisms may be based on principles derivable from spatial regularity and coherence of objects in the three-dimensional world.
Brightness Matching, Brightness Cancellation, and Increment Threshold in the Ehrenstein Illusion
Authors: Spillmann Lothar , Fuld Kenneth , Neumeyer Christa
Published: January 2007

Matching and cancellation techniques were used to measure the relative strength of the Ehrenstein illusion in dark figures on a light background (negative contrast) and light figures on a dark background (positive contrast). Brightness enhancement on the former was shown to be maximally 0.28 log unit (relative to the detection threshold), and darkness enhancement on the latter 0.43 log unit. Values differed little with figure–ground contrast (down to a minimum of ±0.5), but decreased with decreasing level of illumination. The luminance increment (decrement) needed to match the illusory brightness (darkness) was similar in size to the luminance decrement (increment) needed to cancel the illusion. The increment threshold for a small test flash measured in three locations relative to the subjective contour delineating the illusion did not differ systematically. The results are compatible with a neurophysiological explanation of the Ehrenstein illusion in terms of line-induced lateral interaction in hypercomplex receptive fields.
Binocular Cues in the Perception of Distance of a Point Source of Light
Authors: Morrison James D , Whiteside Thomas C D
Published: January 2007

The ability to make egocentric distance estimates of a single point source of light, seen in darkness and without the cues of changing size and luminance, was investigated in sixteen observers. The attenuation required to maintain constant luminance, when the target was viewed from different distances, was shown to follow the inverse square law providing the angle subtended by the light was less than 20 s arc. Distance changes were also simulated by means of a split mirror which produced vergence cues, or by test lenses to provide accommodation cues.

Over the range 0.5 to 9.2 m distance estimates were surprisingly accurate, although there was some overestimation of near and underestimation of far distances. Most observers made good judgements when only convergence cues were varied, whereas no observers made consistently good judgements when only accommodation cues were varied. The difficulties are discussed in terms of the accommodation–convergence link. When distance was simulated by changing convergence and accommodation cues, estimates were not as good as when real distance was changed.

Since good estimates were made with brief target exposures, these judgements were not based on subsequent convergence or accommodation changes. It is suggested that the metric or reference against which the apparently absolute judgements were made was the efferent demand signal associated with a ‘resting’ position of convergence in darkness.
Why the Islands Move
Authors: Hutchins Edwin , Hinton Geoffrey E
Published: January 2007

Micronesian navigators routinely make voyages across large expanses of open ocean. To do this, a navigator must judge both the direction in which he is sailing and the distance he has travelled. The rising and setting points of the stars (and other cues) provide instantaneous information about direction, but distance can only be judged by integrating velocity-related information over time. Micronesian navigators judge distance in a way that seems odd. When they are out of sight of land, they imagine that the canoe is stationary and that the islands move back past them. For each voyage, they ‘attend’ to an island off to the side of the course which is out of sight over the horizon. As they sail, they imagine the island moving back along the horizon changing in bearing until it is imagined to be under the bearing it is known to have from the destination island. Then they know they are near their destination. There is good reason for using a frame of reference whose origin is defined by the boat. We show how it finesses a perceptual paradox–the rising and setting points of the stars do not exhibit motion parallax.
Right-Hemisphere Superiority in the Discrimination of Spatial Phase
Authors: Fiorentini Adriana , Berardi Nicoletta
Published: January 2007

Visual field differences have been investigated in various detection and discrimination tasks for simple sinusoidal gratings or for complex gratings composed of two sinusoids of spatial frequencies f and 3 f. Sinusoidal gratings were employed to evaluate contrast sensitivity, subthreshold summation effects, aftereffects of adaptation to a high-contrast grating, and spatial-frequency discrimination. The tasks with complex gratings were detection of the 3 f component in the presence of a high-contrast f component and spatial-phase discrimination. The stimuli were presented either in the left or in the right visual hemifield. The results indicate a lack of lateralization for detection and spatial-frequency discrimination of sinusoidal gratings, and for the bandwidth of subthreshold summation effects and adaptation aftereffects, whereas the detection of the 3 f component in the presence of a high-contrast f component, as well as spatial-phase discrimination of f + 3 f gratings, show a left-field advantage. This suggests a right-hemisphere superiority in the processing of spatial phase.
Effects of Stimulus Context on Preference Judgements for Salt
Authors: Shepherd Richard , Farleigh Cynthia A , Land Derek G
Published: January 2007

An experiment is reported which confirms earlier findings that the range of stimulus concentration affects the estimate of ideal concentration. The method proposed by Booth et al for reducing range bias has been found to give satisfactory results.
Exorcising the Double-Nail Illusion: Giving up the Ghost
Authors: Ono Hiroshi
Published: January 2007

The principles of visual direction explain the double-nail illusion, without the concept of a ghost image. Also, the stimulus arrangement for the illusion is not perceptually ambiguous for the visual system as Krol and van de Grind claim.
Frequency of Fusion and of Loss of Fusion, and Binocular Depth Perception with Alternating Stimulus Presentation
Authors: Guttmann Josef , Spatz Hanns-Christof
Published: January 2007

Stereoscopic vision was investigated with an experimental design allowing dichoptic stimulus presentation at different frequencies of image alternation. For twenty subjects the frequency of binocular fusion and the frequency of loss of fusion to one stereoscopic image was measured as a function of the convergence angle. In thirteen subjects no dependence of the fusion frequency was found, while seven subjects showed a marked increase of the fusion frequency with increasing angle of convergence. In all cases the frequency of fusion was higher than the frequency of loss of fusion. Both frequencies, however, are lower than the flicker fusion frequency. Under conditions where no monocular cues and no references for stereoptic depth comparisons were presented, the apparent distance of the image from the observer could not be assessed, but perception of relative motion in depth was possible. All subjects assessed the direction of motion accurately down to changes of the convergence angle of 0.2 deg s−1.
The Recency Effect in the Perception of Ambiguous Figures
Authors: Wilton Richard N
Published: January 2007

After a failure to obtain a recency effect in the perception of ambiguous figures three experiments were carried out to determine the conditions which govern the effect. It was found that the duration of the stimulus which precedes the ambiguous figure (the most recent stimulus) was important. Also of importance was the interval between the next-to-most-recent stimulus and the ambiguous figure. The effect of manipulating these variables was such that sometimes no recency effect was obtained, implying that their state is sometimes critical for the effect. Variations in the duration of the ambiguous stimulus did not cause the recency effect to vary. Recommendations are made for the demonstration of a reliable recency effect.
Perceptual Organization in Multistable Apparent Motion
Authors: Ramachandran Vilayanur S , Anstis Stuart M
Published: January 2007

Is motion perception based on a local piecemeal analysis of the image or do ‘global’ effects also play an important role? Use was made of bistable apparent-motion displays in trying to answer this question. Two spots were flashed simultaneously on diagonally opposite corners of a 1 deg wide square and then switched off and replaced by two spots appearing on the other two corners. One can either see vertical or horizontal oscillation and the display is bistable just as a Necker cube is. If several such bistable figures are randomly scattered on the screen and presented simultaneously, then one usually sees the same motion axis in all of them, suggesting the presence of field-like effects for resolving ambiguity in apparent motion.

While viewing a single figure observers experience hysteresis: they tend to adhere to one motion axis or the other and can switch the axis only by looking away and looking back after 10–30 s have elapsed. The figure can be switched off and made to reappear at some other random location on the screen and it is then always found to retain its motion axis. Several such demonstrations are presented to show that spatial induction effects in metastable motion displays may provide a particularly valuable probe for studying ‘laws’ of perceptual organization.
A Moving Display Which Opposes Short-Range and Long-Range Signals
Authors: Mather George , Cavanagh Patrick , Anstis Stuart M
Published: January 2007

A novel display is described which stimulates both the long-range and the short-range motion detecting processes simultaneously, but with opposing directions of movement. The direction in which the stimulus appears to move depends on retinal eccentricity and element size, but adaptation to the display always produces a motion aftereffect (MAE) direction opposite to the direction of the short-range component. The display may offer insights into the properties of the two-process motion detecting system.
The Size Illusion: Visual and Kinaesthetic Information in Size Perception
Authors: Laszlo Judith I , Broderick Pia
Published: January 2007

Earlier studies have shown the size of kinaesthetically presented two-dimensional movement patterns to be significantly overestimated. Whether this size overestimation is characteristic of the kinaesthetic system alone has not been established. Two experiments are reported which were designed to investigate size judgment made after kinaesthetic and visual pattern presentation and the effect of environmental cues on the perception of movement patterns. In experiment 1 patterns were presented kinaesthetically (experimenter guided hand movements around the outline of the pattern) or in combination with visual information given by a moving light (pinpoint light attached to the stylus which was moved around the pattern); visual and kinaesthetic cues were either congruent or conflicting with each other; and environmental cues were either present or absent. In experiment 2 static visual display was compared with visually traced pattern presentation, again with or without environmental cues. Overall the results showed that, regardless of experimental manipulation, in all cases where the information was given over time the subject perceived the pattern larger than reality. After static visual display, overestimation of size did not occur.
Illusory Motions Induced by Rapid Displacements of the Observer
Authors: Farnè Mario , Sebellico Andreina
Published: January 2007

Some illusory effects of movement are described that are easily observable when the subject is in rapid locomotion (driving a car or travelling on a train) and gazes fixedly at a particular point of the scene. These effects are essentially characterized by deformations and displacements of parts of the environment. It is suggested that the phenomenon responsible for them is the loss of size and position constancy, respectively. Experimental evidence indirectly validates this hypothesis, and a program of studies is now under way to further corroborate it.