bluuebunny/crossref_metadata_2025 huggingface dataset:
The Perception of Mirror-Reflected Objects
Authors: Ittelson William H , Mowafy Lyn , Magid Diane
Published: January 2007

In what ways and under what conditions does an object appear to differ from its enantiomorph (its mirror reflection)? This ‘mirror question’ or its popular counterpart, “Why does a mirror reverse left and right but not up and down?” is frequently encountered, but an acceptable answer is not to be found in the literature. The question is approached as an experimental problem in visual psychophysics. A mirror optically reverses the axis perpendicular to its surface. What are the perceptual consequences of this stimulus transformation? This question is examined in four experiments by using stimuli of varying complexity and familiarity. Apparent reversals are demonstrated along right—left, front—back, top—bottom, and oblique axes, depending on the perceived asymmetries of the stimulus object. Perceived asymmetry is shown to depend both on structural asymmetries and on canonical axes and orientations defined by social convention. It is concluded that an object appears to differ from its enantiomorph by an apparent reversal along the axis of least perceived asymmetry. Implications for perceptual frames of reference and for the perception of symmetry are discussed.
Perceived Onset Simultaneity of Stimuli with Unequal Durations
Authors: Jaśkowski Piotr
Published: January 2007

Temporal-order judgment was investigated for a pair of visual stimuli with different durations in order to check whether offset asynchrony can disturb the perception of the order/simultaneity of onset. In experiment 1 the point of subjective simultaneity was estimated by the method of adjustment. The difference in duration of the two stimuli in the pair was either 0 or 50 ms. It was found that the subject shifts the onset of the shorter stimulus towards the offset of the longer one to obtain a satisfying impression of simultaneity even though the subject was asked to ignore the events concerning the stimulus offset. In experiments 2 and 3 the method of constant stimulus was applied. Both experiments indicate that subjects, in spite of instruction, take into account the offset asynchrony in their judgment.
The Influence of Object Familiarity on Magnitude Estimates of Apparent Size
Authors: Predebon John
Published: January 2007

Three magnitude-estimation experiments were used to determine the exponents of the power function relating size judgments and physical size for two-dimensional familiar and unfamiliar stimuli. The exponent of the power function was used to index the effect of familiar size on perceived size under a variety of conditions, from full-cue to reduced-cue viewing conditions. Although the value of the exponents varied across the three experiments, within each experiment the exponent of the familiar stimulus was not significantly different from that of the unfamiliar stimulus, indicating that familiar size does not influence the rate of growth of perceived size. The results of a fourth experiment excluded a possible explanation of the findings of experiments 1–3 in terms of subjects responding to relative angular size as a consequence of the successive presentation of the different-sized representations of the familiar stimulus. Taken together, the present findings are consistent with the hypothesis that the influence of familiar size on estimates of size mainly reflects the intrusion of nonperceptual processes in spatial responses.
Anomalous Spiral Aftereffects: A New Twist to the Perception of Rotating Spirals
Authors: Broerse Jack , Dodwell Peter , Crassini Boris
Published: January 2007

Stationary spirals viewed after inspecting rotating sectored disks appear to rotate and to expand or contract radially, even though the rotating disks contain no perceptible components of radial motion. Moreover, the relative directions of illusory rotation and radial motion observed in these instances are ‘impossible’ under the stimulus constraints normally imposed by the geometry of a spiral under rotation: the stationary spirals appeared to expand/contract in directions opposite to those normally observed under conditions of actual spiral rotation, and under conditions of illusory spiral rotation in classical spiral aftereffects.
Movement and Proximity Constrain Miscombinations of Colour and Form
Authors: Baylis Gordon C , Driver Jon , McLeod Peter
Published: January 2007

A relatively frequent error when reporting brief visual displays is to combine presented features incorrectly. It has been proposed that Gestalt grouping constrains such errors so that miscombined features tend to come from the same perceptual group. In three experiments it was examined whether this principle applies to grouping by motion, and to grouping by proximity. Miscombinations of colour and form were more likely to consist of a colour and form that had moved in the same direction than features which had moved in opposite directions. Miscombinations were also more likely for adjacent items. The implications of these results for the mechanisms of feature integration are discussed.
Amodal Completion, Depth Stratification, and Illusory Figures: A Test of Kanizsa's Explanation
Authors: Purghé Franco , Coren Stanley
Published: January 2007

Subjective contours have been explained by Kanizsa as being a consequence of amodal completion of incomplete figures. According to the theory of amodal completion, figural incompleteness triggers the emergence of an illusory object superimposed on the gaps in the inducers, which in turn hide parts of the pattern, thus suggesting that the plane of the illusory object must always be seen to be above the plane of the inducers. A figure was created in which subjective contours are seen despite the fact that the perceived depth relationships run counter to that required by the theory of amodal completion. In four experiments, this depth relationship is confirmed by using direct and indirect measures which assess both registered and apprehended depth. By emphasizing a logical inconsistency in the explanation based on amodal completion, the results show that amodal completion, at least in Kanizsa-like patterns, cannot be considered as a causal factor for subjective contour figures.
Lateral Masking as a Determinant of Global Dominance
Authors: Podrouzek K Wayne , Modigliani Vito , Di Lollo Vincent
Published: January 2007

The term compound letter refers to a large (global) letter made up of small (local) letters. Reaction time to identify local letters is longer when local and global letters are different than when they are the same (the global dominance effect). The possible contribution of lateral masking to this effect was investigated. Lateral masking denotes reduced probability of identifying a stimulus when it is closely surrounded by other stimuli (as is the case for the local items in a compound stimulus). Three experiments were conducted in which the dependent measure was percentage of correct responses, rather than reaction time. In experiment 1 compound letters were used; accuracy of performance yielded evidence of global dominance such as obtained with reaction time measures. In experiments 2 and 3 the strength of lateral masking in geometrical forms was varied by varying the density of their component items. In agreement with earlier suggestions based on indirect evidence, the results directly implicated lateral masking as an important determinant of global dominance. However, lateral masking could not account fully for the experimental outcome. Factors beyond lateral masking, such as global precedence in the processing sequence or inhibitory interactions among low and high spatial-frequency components of the compound images are required in order to provide a comprehensive account of global dominance effects.
Depth Perception of Interfering Periodic Patterns: A Possible Contribution to Disorientation on Escalators
Authors: Munck-Fairwood Roger C
Published: January 2007

Incongruous and illusory depth cues, arising from ‘interference patterns’ produced by overlapping linear grids at the edges of escalator treads, may contribute to the disorientation experienced by some escalator users, which in turn may contribute to the causes of some of the many escalator accidents which occur. The apparent depth of the interference pattern from the viewer is analysed in terms of the cues deriving from size and viewer motion. Both of these cues support the depth of the target being infinite. Preliminary observations are reported which confirm this analysis. Remedies for the problem are suggested. The possible contribution of this illusion to disorientation on escalators, due to misjudgment of depth, is compared with another recently reported factor which is due to stereoscopic miscorrespondence of periodic targets.
The Role of Depth Stratification in the Solution of the Aperture Problem
Authors: Bressan Paola , Ganis Giorgio , Vallortigara Giorgio
Published: January 2007

When a plaid pattern composed of a stationary vertical grating and a horizontally drifting diagonal grating is shown behind a circular aperture, the pattern appears to move coherently in a vertical direction. When the bars of the stationary grating are narrower than those of the moving grating, only the latter is seen to move, in a direction orthogonal to its orientation (ie diagonal); but when the bars of the stationary grating are wider than those of the moving grating, vertical motion of the whole plaid predominates. It is argued that, in the absence of occlusion information, the motion of a plaid within an aperture depends on the unambiguous displacement of inner line terminators at the crossings of the two gratings. Relative motion and differences in bar width between the two gratings provide information about which set of bars is in front of the other. When these sources of information are consistent with each other, separation of the two gratings in depth occurs: inner line terminators no longer perceptually exist and the direction of motion becomes determined only by terminators at the edges, which causes a shift from vertical to orthogonal motion. Differences in luminance also provide (asymmetrical) information about depth relationships: when darker bars occlude lighter bars, the probability of orthogonal motion increases as a function of the difference in luminance, whereas when lighter bars are over darker bars, vertical motion prevails.
Perceiving Surface Orientation: Pictorial Information Based on Rectangularity Can Be Overriden during Observer Motion
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

Although the observer's motion can elicit perception of relative depth, it is less successful in doing so when competing pictorial information is available. However, the evidence for this may be affected by limited extents of motion and by equidistance tendencies. Results obtained when monocular observers judged the orientation-in-depth of trapezoidal and of rectangular surfaces, during lateral head motion of extents 0 cm to 30 cm, are described. When the motion extent was less than 30 cm, trapezoidal surfaces were misperceived because they were interpreted as rectangular; this pictorial information was overriden only when the motion extent was 30 cm. The results may reflect the sequential nature of motion information and the redundancy of information in normal viewing: pictorial information may take precedence when motion is limited, but motion information can be indefinitely augmented. Comments are directed to (i) the use of Ames ‘distorted rooms’ in this area of research, and (ii) the ‘ecological’ interpretation of pictorial information.
Recognition of Complex Auditory-Spatial Patterns
Authors: Lakatos Stephen
Published: January 2007

Two experiments were carried out to investigate the perception of complex auditory-spatial patterns. Subjects were asked to identify alphanumeric characters whose patterns could be outlined acoustically through the sequential activation of specific units in a speaker array. Signal bandwidths were varied systematically in both experiments. Signals in experiment 1 had sharp onsets and offsets; envelope shapes in experiment 2 were much more gradual. Subjects showed considerable ability in recognizing alphanumeric patterns traced with signals of varying acoustical composition. Reductions in the steepness of signal attack and decay produced limited declines in pattern recognition ability. Systematic trends in the relation between patterns and the distribution of incorrect responses suggest that subjects performed a pattern-matching task, in which identifications were made on the basis of component features. The unexpected pattern recognition abilities that subjects demonstrated in both experiments suggest that spatial hearing, like vision, has access to mechanisms for amodal spatial representations.
Evidence for Representations of Perceptually Similar Natural Categories by 3-Month-Old and 4-Month-Old Infants
Authors: Quinn Paul C , Eimas Peter D , Rosenkrantz Stacey L
Published: January 2007

The paired-preference procedure was used in a series of experiments to explore the abilities of infants aged 3 and 4 months to categorize photographic exemplars from natural (adult-defined) basic-level categories. The question of whether the categorical representations that were evidenced excluded members of a related, perceptually similar category was also investigated. Experiments 1–3 revealed that infants could form categorical representations for dogs and cats that excluded birds. Experiment 4 showed that the representation for cats also excluded dogs, but that the representation for dogs did not exclude cats. However, a supplementary experiment showed that the representation for dogs did exclude cats when the variability of the dog exemplars was reduced to match that of the cat exemplars. The results are discussed in terms of abilities necessary for the formation of more complex categorical representations.
New Depth to the Müller-Lyer Illusion
Authors: Glennerster Andrew , Rogers Brian J
Published: January 2007

It is demonstrated that when the two halves of the Müller-Lyer illusion are shown separately to the two eyes this can result in a perception of the binocularly viewed shaft as slanted in depth. For short fin lengths, the magnitude of this slant can be predicted by the extent of the ordinary two-dimensional illusion. This result is discussed in relation to Julesz's claim that stereoscopic matching of the images in the two eyes must precede whatever process is responsible for the Müller-Lyer illusion (whereas the reported illusion seems to imply the reverse). The cyclopean Müller-Lyer demonstration on which Julesz's argument is based is reexamined. It is suggested that the matching of coarse-scale features in the images in the two eyes may help to explain both the cyclopean and the reported three-dimensional Müller-Lyer illusion.
Recognition of Animal Locomotion from Dynamic Point-Light Displays
Authors: Mather George , West Sophie
Published: January 2007

To date, studies of biological motion have been restricted to displays of humans filmed (or synthesised by computer) with lights attached at the major joints. Observers can readily extract meaning from such displays. There have been no studies to assess the generality of this ability by assessing observers' accuracy in identifying various animals solely on the basis of biological motion. An experiment is reported for which biological-motion displays were created from the stop-action photographs taken by Muybridge in the last century. Naive observers could reliably identify the animals involved when biological-motion displays were animated, but not when they were given static views of dot positions. Thus the ability to interpret biological motion is general and is not restricted to human movements.
Stereoscopic Slant Reversals: A New Kind of ‘Induced’ Effect
Authors: Gillam Barbara
Published: January 2007

Data are presented from three experiments confirming an earlier finding that the stereoscopic slant perceived may be opposite to the geometrically predicted direction of slant (Gillam 1967). The stimulus for stereoscopic slant was created by imposing a disparity gradient on a frontal plane surface. Reversals are shown to occur readily for slants around a vertical axis but rarely for slant around a horizontal axis. Reversal frequency is greater for surfaces which have a regular pattern, providing good perspective information about slant. Cue conflict cannot explain reversals because adherence to perspective information predicts a perception of zero slant rather than reverse slant. A new explanation has been proposed attributing reversals to the ambiguity of horizontal disparity gradients and disambiguation of the disparity gradient by its relationship to the perspective gradient. It is shown that for any given disparity gradient there is a physical surface which would give rise to a slant reversed with respect to that normally predicted. Such a surface is eccentric in the field of view, with eccentricity given by the difference between the slants signalled by the disparity gradient and the perspective gradient. This explains why reversal responses to disparity gradients occur in the presence of perspective. It is proposed, on the basis of this analysis and the fact that reversals occur, that, like convergence and vertical disparity, perspective is a factor contributing to the correct scaling of disparity gradients in the horizontal meridian with respect to surface eccentricity.
How the Range Effect Contaminates Control Scores in Studies of Visual Illusions
Authors: Hotopf W H Norman , Brown Susannah A
Published: January 2007

The relationship between mean control scores and mean experimental scores in 23 experiments on alignment illusions has been examined. Evidence is presented to show that, through the operation of the range effect, control scores are biased to a significant degree in the direction of experimental scores. The implications of this are considered, not only as regards the value of control scores in psychophysical studies, but also as further evidence of the dangers of within-subjects experimental designs when issues depend upon the values of extreme points in a range of values.
Quantitative Perceptual Estimates: Verbal versus Nonverbal Retrieval Techniques
Authors: Leibowitz Herschel W , Guzy Lawrence T , Peterson Ellen , Blake Patrick T
Published: January 2007

Examples of the inaccessibility of mental processes by means of verbal recall are described with particular reference to the accuracy of quantitative estimates of size, distance, and duration. Evidence is presented in support of the hypothesis that nonverbal retrieval techniques are more accurate than quantitative verbal estimates. Implications for the judicial process are considered.
Cross-Modal Transfer of Sequential Visual and Haptic Shape Information by Clumsy Children
Authors: Newnham Carol , McKenzie Beryl E
Published: January 2007

The ability of clumsy children aged 9 to 13 years to transfer sequential shape information between the haptic and visual modalities was examined in a matching-to-sample task. In both modalities, spatiotemporal integration of information relevant for shape was involved and transfer was examined between them by using intramodal transfer scores as covariates. The responses of clumsy children were not different from those of nonclumsy children of similar age, sex, and intelligence in the cross-modal condition involving matching of a haptic standard to a visual shape. However, when matching a visual standard to a haptic shape they were consistently both faster and less accurate. It was concluded that a specific visual-to-haptic translation process possibly involving poor visual memory for shape distinguishes clumsy children from their nonclumsy peers.
Preattentive Processing of Object Size: Implications for Theories of Size Perception
Authors: Stuart Geoffrey W , Bossomaier Terence R J , Johnson Sue
Published: January 2007

Information about the visual angle size of objects is important for maintaining object constancy with variations in viewing distance. Although human observers are quite accurate at judging spatial separations (or cross-sectional size), they are prone to error when there are other spans nearby, as in classical illusions such as the Müller-Lyer illusion. It is possible to reconcile these aspects of size perception by assuming that the size domain is sampled sparsely. It was shown by means of a visual search procedure that the size of objects is processed preattentively and in parallel across the visual field. It was demonstrated that an object's size, rather than its boundary curvature or spatial-frequency content, provides the basis for parallel visual search. It was also shown that texture borders could be substituted for luminance borders, indicating that object boundaries at the relevant spatial scale provide the input to size perception. Parallel processing imposes a severe computational constraint which provides support for the assumption of sparse sampling. An economical model based on several broadly tuned layers of size detectors is proposed to account for the parallel extraction of size, the Weberian behaviour of size discrimination, and the occurrence of strong interference effects in the size domain.
Nonstationarity and the Measurement of Psychophysical Response in a Visual Inspection-Time Task
Authors: Deary Ian J , Caryl Peter G , Gibson Gavin J
Published: January 2007

Inspection time (IT) is an index of speed of early visual processing that correlates significantly with measures of higher cognitive ability. An obstacle to the understanding of this important association is the lack of an agreed mechanistic model of the processes involved in IT performance. It is argued here that, whereas in current attempts to model IT processing, stationarity in IT performance is assumed, it is necessary to address this key issue empirically. Two practised subjects undertook 38 400 trials on a standard two-choice visual IT discrimination task. Testing was spread evenly over 60 days. Isotonic regression analysis revealed that both subjects showed nonstationarity in performance over very long periods. The results were not merely due to long-term practice effects; one subject improved in some durations but worsened at others. Therefore, current attempts at modelling in which stationarity in IT performance is assumed must be altered to incorporate the temporal dynamics of IT performance, which might have individual differences.
The Perception of Spatial Structure with Oblique Viewing: An Explanation for Byzantine Perspective?
Authors: Derȩgowski Jan B , Parker Denis M , Massironi Manfredo
Published: January 2007

Earlier work has confirmed that (i) observers can judge divergent receding lines, placed directly in front of them, to be parallel, and (ii) converging lines which are displaced laterally, so that they are viewed obliquely, can also be judged to be parallel. The former observation is in accord with traditional views of perspective while the latter, which is in accord with the depictions of objects found in Byzantine painting, is not in accord with perspective but is predicted by the relative magnitude of the visual angles subtended by the near and far ends of the pair of lines. To investigate whether these effects occurred when the stimulus was clearly three-dimensional, experiments were conducted with a novel apparatus, consisting of a framework of computer-controlled motor-driven luminous rods. This could be remotely adjusted so that all visible sides appeared to be parallel, ie to resemble a cube. Results showed that observers set the sides of this trapezohedron framework as diverging when it was viewed immediately in front of them, a result which is concordant with linear perspective, ie they see the normal projection of a cube as having converging edges. When the framework was displaced from the median plane so that it was viewed obliquely, the sides were set as converging and the magnitude of this effect was significantly related to angle of view, ie observers see the normal projection of a cube as having diverging sides. These results confirm the suggestion that ‘Byzantine perspective’ is a legitimate reflection of perceptual experience, but they do not provide an explanation why the perception of laterally viewed objects was adopted as a model for centrally depicted patterns.
Visual Processing of Facial Distinctiveness
Authors: Benson Philip J , Perrett David I
Published: January 2007

Three experiments are reported in which the role of facial distinctiveness in line-drawing representations of famous faces has been examined. In the first subjects were asked to select their impressions of best likeness interactively from a continuous range of drawings generated in real-time. On average, 42% of caricatures were considered to be the best likeness of famous individuals. The distinctiveness of the target faces related by independent observers correlated with the degree of exaggeration faces received to produce an optimal likeness. More distinctive faces required less caricaturing. In the second experiment caricature levels chosen as best likenesses were investigated. Caricatures of famous faces were recognised more quickly (by 36% of subjects) and more accurately (by 28%) than the true veridical drawings. Thus caricature enhancement can improve recognition in terms of both speed and accuracy. In the third experiment the role of distinctiveness and its interaction with external and internal facial features was investigated. The external (outer) hairline present in the previous experiment was found to provide a powerful frame of reference for the perceptual assessment of individuals' appearances; estimations of best likeness without external features present were, on average, veridical. It is concluded that accurate line drawings of even highly familiar faces are poor at conveying identity. Distinctiveness enhancement improves their likeness and their recognisability. Such caricatured drawings provide improved access to memories of famous faces, which lends strong support to models of human-face memory and processing based on norm-based coding. When required to decide upon the veracity of line drawings based only upon internal features subjects were able to make accurate judgments of veridicality. As well as validating the interaction approach to best-likeness judgments, this result further indicates the difficulty in making judgments of identification based on piecemeal and sparse configural information.
Long-Range Apparent Motion as a Result of Perceptual Organisation
Authors: Oyama Tadasu , Naito Katsuo , Naito Hiromi
Published: January 2007

Five kinds of percept have been found to occur when two different stimulus objects are simultaneously presented, exchanging positions with each other in successive exposures. These five percepts can be classified as follows: (i) Appearance—Disappearance (succession), (ii) Lateral Motion, (iii) Depth Motion, (iv) Transmutation (in colour, brightness, and/or shape), and (v) Overlapping (simultaneity). Results of three experiments indicate that relative dominance among these five percepts systematically depends upon differences between the two stimulus objects in colour, luminance, shape, and size. The relative dominance depended upon the stimulus onset asynchrony (SOA) between successive presentations and on the spatial separation between the two objects. Lateral Motion became more dominant as a result of (a) an increase in the number of stimulus attributes differing between the two objects, (b) an increase in the SOA, or (c) a decrease in the distance between the two objects. Colour difference, even without a luminance difference, was one of the determinants for Lateral Motion. Depth Motion frequently occurred when the two objects differed in size and the SOA and the distances between them were relatively great. Transmutation occurred when the objects differed in colour, luminance, or shape. Perceptual modes (ii) to (iv) can be understood as different results of perceptual organisation that always maintains perceptual identity of objects and maintains perceptual constancy of their attributes as much as possible. Long-range apparent motion could be a result of such perceptual organisation.
Effects of Attention on Perception of Features and Figural Organisation
Authors: Tsal Yehoshua
Published: January 2007

Four studies are reported that demonstrate effects of attention on early perceptual processes. These studies show that directing attention to stimulus location influences perceived brightness, perceived length, and the overall organisation of the Müller-Lyer figure and ambiguous figures. Since in all four studies the dependent measure was dissociated from the attentional instructions, the results are not open to traditional criticism of late-selection advocates, and therefore provide strong support for early-selection views of attention.
Invariance from the Euclidean Geometer's Perspective
Authors: Van Gool Luc J , Moons Theo , Pauwels Eric , Wagemans Johan
Published: January 2007

It is remarkable how well the human visual system can cope with changing viewpoints when it comes to recognising shapes. The state of the art in machine vision is still quite remote from solving such tasks. Nevertheless, a surge in invariance-based research has led to the development of methods for solving recognition problems still considered hard until recently. A nonmathematical account explains the basic philosophy and trade-offs underlying this strand of research. The principles are explained for the relatively simple case of planar-object recognition under arbitrary viewpoints. Well-known Euclidean concepts form the basis of invariance in this case. Introducing constraints in addition to that of planarity may further simplify the invariants. On the other hand, there are problems for which no invariants exist.
A New Twist on the Rotating-Trapezoid Illusion: Evidence for Neural-Adaptation Effects
Authors: Long Gerald M , Toppino Thomas C
Published: January 2007

In a series of experiments, the selective-adaptation paradigm was applied to the rotating-trapezoid illusion in an effort to demonstrate neural-adaptation effects in the figural reversal of this classic illusion. Prior to viewing the standard trapezoid, the observer adapted to a rectangle rotating unambiguously in the same direction as the trapezoid or in the opposite direction. In accordance with the neural hypothesis, illusion strength was greatest when the two figures rotated in the same direction and weakest when the two figures rotated in opposite directions. Results were confirmed with two separate dependent variables: the observer's ‘first look’ at the illusion after adaptation and the observer's reversal rate during a test period. These findings were discussed in terms of (a) the basic similarity of results for the rotating trapezoid and reversible figures such as the Necker cube and (b) the need for a multiprocess model of both classes of illusions which emphasizes bottom—up and top—down processes.
Intraattribute and Interattribute Motion Induction
Authors: von Grünau Michael , Faubert Jocelyn
Published: January 2007

The phenomenon of motion induction occurs, for example, when a bar that is presented next to a spot, which itself was presented slightly earlier, is not correctly perceived to appear everywhere simultaneously, but seems to grow out of the spot. The spot is said to prime one end of the bar. Experiments have been designed to throw more light on the local and global aspects of this phenomenon, in particular to establish whether this illusory motion percept can be observed when the spot and the bar stimuli are defined with respect to the background by one of a variety of attributes, such as luminance, color, stereodepth (crossed and uncrossed), texture, and motion (start and stop). It was found that all attribute combinations supported motion induction readily, but that the strength of the perceived motion (as measured by magnitude estimation) varied and depended more on the attribute defining the bar than on the attribute of the spot. Luminance and color gave the most vivid effects, whereas motion and depth showed the least vivid effects. The influence of the amount of luminance and color contrast on the strength of the effect was also determined and it was found that these variables affected motion induction most at very low contrast levels close to detection threshold. It is concluded that the illusory motion in this effect depends only slightly on the particular visual attribute channel that carries the stimulus information. This is consistent with the contention that it is a high-level, attention-related effect, phenomenologically similar to polarized gamma movement.
Ambiguous Pictorial Depth Cues and Perceptions of Nonrigid Motion in the Three-Loop Figure
Authors: Broerse Jack , Li Rongxin , Ashton Roderick
Published: January 2007

The three-loop figure is a two-dimensional (2-D) pattern that generates (mis)perceptions of nonrigid three-dimensional (3-D) structure when rotated about its centre. Such observations have been described as counterexamples to the principle whereby a moving object is presumed to be rigid, provided that a rigid interpretation is possible (ie the ‘rigidity constraint’). In the present investigation we demonstrated that stationary three-loop figures exhibit many of the classic properties of multistable/ambiguous figures, with any one of several possible 3-D configurations being reported at any one instant. Further investigation revealed that perceived nonrigidity during rotation was markedly reduced (and rigidity enhanced) when the figure was modified with static pictorial depth cues (eg shading, interposition). These cues had no effect on the overall proportion of time that observers reported 3-D organisations in stationary versions of the figure, but significantly reduced the frequency of perceptual reorganisation, and increased the duration for reporting a particular organisation. Since each of the perceived 3-D structures in a stationary ambiguous 2-D figure has a unique kinetic counterpart (ie rigid transformation), we attribute the nonrigid structure perceived when the figure rotates to the integration of these otherwise inconsistent kinetic components; and have further illustrated this with modified versions of a Penrose impossible triangle. Under kinetic versions of the classical size/distance invariance hypothesis, the rigidity constraint may be considered to represent a special instance of size/shape constancy, in which case counterexamples involving (mis)perceptions of nonrigid structure are comparable to other well-known exceptions to such principles of minimum object change (eg classical illusions).
A Transparent Motion Aftereffect Contingent on Binocular Disparity
Authors: Verstraten Frans A J , Verlinde Reinder , Fredericksen R Eric , van de Grind Wim A
Published: January 2007

Under transparent motion conditions overlapping surfaces are perceived simultaneously, each with its own direction. The motion aftereffect (MAE) of transparent motion, however, is unidirectional and its direction is opposite to that of a sensitivity-weighted vector sum of both inducing vectors. Here we report a bidirectional and transparent MAE contingent on binocular disparity. Depth (from retinal disparity) was introduced between two patterns. A fixation dot was presented at zero disparity, that is, located between the two adaptation patterns. After adaptation to such a stimulus configuration testing was carried out with two stationary test patterns at the same depths as the preceding moving patterns. For opposite directions a clear transparent MAE was perceived. However, if the adaptation directions were orthogonal the chance of a transparent MAE being perceived decreased substantially. This was subject dependent. Some subjects perceived an orthogonal transparent MAE whereas others saw the negative vector sum—an integrated MAE. In addition the behaviour of the MAE when the distance in depth between adapting and test patterns was increased was investigated: it was found that the visibility of the MAE then decreased. Visibility is defined in this paper as: (i) the percentage of the trials in which MAEs are perceived and (ii) the average MAE duration. Both measures decreased with increasing distance. The results suggest that segregation and integration may be mediated by direction-tuned channels that interact with disparity-tuned channels.
Auditory Aftereffects following Simulated Motion Produced by Varying Interaural Intensity or Time
Authors: Ehrenstein Walter H
Published: January 2007

Simulated auditory motion, ie step-ramp modulated interaural intensity (Δ I) or time (Δ t) was presented via headphones as an adapting stimulus (narrow-band signal of 1 kHz mean frequency). After adaptation, settings of a stationary test stimulus were systematically shifted in the opposite direction when the experimental parameter was Δ I, but not when it was Δ t. Further studies with Δ t motion with the use of mean frequencies of 100 Hz or 6 kHz showed an aftereffect only at 6 kHz. Unlike visual motion aftereffects, no counter-motion was observed; rather the test stimulus appeared stationary, but settings of its interaural midline were displaced in a direction opposite to the direction of adaptation (on average by 1.2 dB or 30 μs for Δ I-simulated and Δ I-simulated motion, respectively). This displacement effect decayed with time after adaptation. The frequency dependence found for Δ t motion suggests that the low-frequency mechanism of directional hearing that uses interaural ongoing-time (phase) differences is not able to adapt. The observed auditory aftereffects may be analogous to visual motion aftereffects since they are direction specific; however, because they lack apparent motion they also resemble disparity-specific stereoscopic aftereffects.
Depth from Binocular Rivalry without Spatial Disparity
Authors: Howard Ian P
Published: January 2007

Some new stereoscopic effects are reported that arise from dichoptic stimuli containing no binocular disparity. In one effect, identical arrays of small black discs are presented to the two eyes and slightly smaller white discs are superimposed on one of each pair of black discs. This creates the impression of a surface with holes in it, through which is seen a surface with fluctuating black and white areas. This is referred to as the ‘sieve effect’. The white discs must subtend less than about 1 deg of visual angle. With larger discs the black and white areas no longer exhibit alternating rivalry but combine to produce binocular lustre. This destroys the sieve effect. The sieve effect is weak or nonexistent when the black and white discs are the same size, showing that well-defined binocular rims are required for the effect. When the monocular white discs are reduced to dots, the impression of a surface seen through holes gives way to the impression of an array of dots behind or standing out from the background. In this case the monocular dots permanently dominate the homogeneous backgrounds in the other eye and the impression of depth can be explained in terms of apparent parallax or of disparity due to the instability of vergence.
Visual Processing of the Motion of an Object in Three Dimensions for a Stationary or a Moving Observer
Authors: Regan David , Hamstra Stanley J , Kaushal Suneeti , Vincent Alex , Gray Robert , Beverley Kenneth I
Published: January 2007

A rate of change of relative disparity is a sufficient binocular stimulus for the perception of motion in depth. For motion within the meridian that contains the eyes, disparity change associated with approaching motion is processed through four channels, each tuned to a different direction of motion in depth. Directional discrimination is most acute but detection sensitivity falls to a minimum for a trajectory passing approximately midway between the eyes. This can be explained if discrimination depends on the relative activity of the four channels. Two binocular retinal-image correlates of the direction of the motion of an object in depth are the ratio between the velocities of the retinal images of the object in the left and right eyes [(dφ/d t)R/(dφ/d t)L], and the ratio between the translational velocity of the binocularly fused image and the rates of change of disparity [(dφ/d t)/(dγ/d t)]. Directional discrimination is possible by using the second cue alone. An isotropic rate of expansion of the retinal image is a sufficient monocular stimulus for the perception of motion in depth. There is no evidence that expansion is processed through channels tuned to the direction of motion in depth. Two monocular correlates of the direction of the motion of an object in depth are the ratio between the translational velocity and the rate of expansion of the retinal image of the object [(dφ/d t)/(dθ/d t)], and the ratio between the velocities of opposite edges of the retinal image [(dα1/dt)/(dα2/d t)]. Subjects are able monocularly to discriminate the direction of motion in depth with high acuity (better than 0.1 deg threshold) in the vertical, horizontal, or oblique meridians, even when the direction and the speed of translational motion are removed as cues. Visual discrimination of time to contact with an approaching object can be disconfounded from discrimination of its rate of expansion and vice versa with a threshold separation ratio of as much as 100:1.
Depth Relief
Authors: Koenderink Jan J , van Doorn Andrea J , Kappers Astrid M L
Published: January 2007

A study is reported of the depth relief in a simple three-dimensional scene consisting of a white, rough sphere on a planar support, illuminated in a natural manner. Viewing conditions included monocular and binocular as well as ‘synoptical’ viewing. In the synoptical condition the eyes are optically superimposed. The local surface attitude was probed via a gauge figure that had to appear as a circle painted upon the surface of the object. The measurements allow a reconstruction of the depth relief, which can be compared with the (known) range map. Idiosyncratic differences between three subjects were found that are the exact reverse of what was found for these same subjects for the case of pictorial relief reported in an earlier paper. Apparently the subjects put different weights on sources of sometimes conflicting, sometimes corroborative evidence. The relief is deepest for binocular vision, flatter for monocular vision, and flatter still for synoptical vision. Deviations from veridicality that cannot be explained by mere depth scaling exist and may be due to the nature of the monocular cues.
The Theory of the Curvature-Constraint Line for Amodal Completion
Authors: Takeichi Hiroshige , Nakazawa Hitoshi , Murakami Ikuya , Shimojo Shinsuke
Published: January 2007

Amodal completion of partly occluded figures is analyzed as natural computation. Here amodal completion is shown to consist of four subproblems: representation, parsing, correspondence, and interpolation. Second, each problem is shown to be basically solvable on the basis of the generic-viewpoint assumption. It is also argued that the interpolation problem might be the key problem because of mutual interdependence among the subproblems. Third, a theory is described for the interpolation problem, in which the generic-viewpoint assumption and the curvature-consistency assumption are presumed. The generic-viewpoint assumption entails that the orientation and the curvature should not change at the point of occlusion. The curvature-consistency assumption entails that the hidden contour should have the minimum number of inflections to maintain continuity in orientation and curvature. The shape of the interpolated contour represented qualitatively in terms of the number of inflections can uniquely be determined when the location of the terminators and local orientation and curvature of the visible contours at the terminators are given. Fourth, it is shown in an instant psychophysics that the theory is highly consistent with human performance.
Perceiving the Orientation in Depth of Real Surfaces: Background Pattern Affects Motion and Pictorial Information
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

Motion information contributes weakly to veridical depth perception of real stimuli. To test whether background pattern might enhance veridicality, observers judged the orientations in depth of pictorially matched trapezoidal and rectangular surfaces, with and without a rectangular grid of vertical stripes in a frontal plane behind surfaces; viewing was monocular with lateral head motions of 15 cm extent. The grid did not enhance veridicality; instead, surfaces actually or pictorially slanted to the frontal plane were judged more slanted with the grid present. In a second experiment, observers were static or moved through 30 cm; the grid had little effect during stasis, but again elicited judgments of greater slant during motion, despite broadly veridical responses without the grid. Results from actual slant are interpreted in terms of motion contrast and suggest that motion information may be important in conveying differences in orientation. Results from pictorial slant suggest that the influence of pictorial information increases as its complexity increases.
Perceptual Latency and Complex Random-Dot Stereograms
Authors: Bradshaw Mark F , Rogers Brian J , De Bruyn Bart
Published: January 2007

Naïve observers of random-dot stereograms depicting complex surfaces often find that they require several tens of seconds before the impression of depth emerges. With practice, however, perception times often decrease markedly: perceptual learning occurs. Current explanations of these effects were assessed in two experiments. In the first experiment the perception times of naïve observers for random-dot stereograms which depicted the same complex shape but contained different ranges of disparity were measured. In the second experiment the minimum times required by experienced observers to perceive a given complex shape in stereograms that contained different ranges of disparity were determined. Perception times for the naïve observers were all very fast (<3 s) and showed no evidence of perceptual learning. There was no effect of disparity range on perception times in either experiment. It was found that very large-disparity (80 min arc) complex stereograms could be perceived quickly, even by naïve observers. It is concluded that the long initial latencies previously reported are not due to surface complexity nor to the range of disparities present. Other factors, such as dot size, dot density, and the correlation of the stereo images, appear to be important determinants of efficient stereoscopic performance when viewing complex random-dot stereograms.
A Structure-from-Motion Scheme That Looks for Parallels, and its Implications for Apparent Reversals in Rotating Trapezia
Authors: Cowie Roddy
Published: January 2007

Apparent reversals in rotating trapezia have been regarded as evidence that human vision favours methods which are heuristic or form dependent. However, the argument is based on the assumption that general algorithmic methods would avoid the illusion, and that has never been clear. A general algorithm for interpreting moving parallels has been developed to address the issue. It handles a considerable range of stimuli successfully, but finds multiple interpretations in situations which correspond closely to those where apparent reversals occur. This strengthens the hypothesis that apparent reversals may occur when general algorithmic methods fail and heuristics are invoked as a stopgap.
“The Analogy between Stereo Depth and Brightness”: A Reexamination
Authors: Lunn Peter D , Morgan Michael J
Published: January 2007

A forced-choice experiment is reported, the results of which demonstrate that the cyclopean analogues of the Hermann grid, the embedded squares, and Mach bands can be readily observed. It is concluded that the earlier failure by Brookes and Stevens to observe these cyclopean analogues does not prove that spatial filtering of horizontal disparity is fundamentally different from the spatial filtering of the luminance image.