bluuebunny/crossref_metadata_2025 huggingface dataset:
The ‘Uniqueness Constraint’ and Binocular Masking
Authors: McKee Suzanne P , Bravo Mary J , Smallman Harvey S , Legge Gordon E
Published: January 2007

In stereo-matching algorithms, the ‘uniqueness constraint’ requires that a feature in one stereo half-image be matched to, at most, one similar feature in the other half-image. Experiments are reported in which binocular contrast thresholds and depth-discrimination judgments have been used to determine whether the human stereo system makes unique matches. A single high-spatial-frequency target in the left eye was paired stereoscopically with two identical targets, presented near retinal correspondence (±3.5 min of disparity), in the right eye. Contrast-increment thresholds were measured for each of the targets in the right eye, and it was found that the target in the left eye masked both. Indeed, the amount of binocular masking for each member of the double target nearly equaled the masking observed when only a single target was presented to the right eye. Depth judgments confirmed that the target in the left eye had been matched to both targets in the right eye. It is concluded that uniqueness is not an absolute constraint on human stereo matching.
The Relationship between Stereoacuity and Stereomotion Thresholds
Authors: Cumming Bruce G
Published: January 2007

There are in principle at least two binocular sources of information that could be used to determine the motion of an object towards or away from an observer; such motion produces changes in binocular disparities over time and also generates different image velocities in the two eyes. It has been argued in the past that stereomotion is detected by a mechanism that is independent of that which detects static disparities. More recently this conclusion has been questioned. If stereomotion detection in fact depends upon detecting disparities, there should be a clear correlation between static stereo-detection thresholds and stereomotion thresholds. If the systems are separate, there need be no such correlation.

Four types of threshold measurement were performed by means of random-dot stereograms: (1) static stereo detection/discrimination; (2) stereomotion detection in dynamic random-dot stereograms (temporally uncorrelated); (3) stereomotion detection in temporally correlated random-dot stereograms; and (4) binocular detection of frontoparallel motion. Three normal subjects and five subjects with unusually high stereoacuities were studied. In addition, two manipulations were performed that altered stereomotion thresholds: changes in mean disparity, and image defocus produced by positive spectacle lenses. Across subjects and conditions, stereomotion thresholds were well correlated with stereo-discrimination thresholds. Stereomotion was poorly correlated with binocular frontoparallel-motion thresholds. These results suggest that stereomotion is detected by means of registering changes in the output of the same disparity detectors that are used to detect static disparities.
Integration of Stereo, Texture, and Outline Cues during Pinhole Viewing of Real Ridge-Shaped Objects and Stereograms of Ridges
Authors: Frisby John P , Buckley David , Horsman Janet M
Published: January 2007

Three experiments are reported in which the possible role of blur cues as a factor needing to be taken into account in cue-integration studies involving conflicts between stereo and texture/outline cues was investigated. The earlier suggestion was tested that uncontrolled blur cues might have caused the quite different patterns of cue integration reported for real ridge-shaped objects oriented vertically and for stereograms depicting similar surfaces. Blur cues were manipulated by pinhole viewing intended to render accommodation open loop. The results for real ridges were as predicted by the blur-cue hypothesis: pinhole viewing strengthened texture/outline cues in vertically oriented ridges, thereby diminishing the pattern of stereo dominance hitherto observed for these stimuli (and as observed here in non-pinhole-viewing control conditions and in horizontally oriented ridges). The results for the stereograms did not conform to predictions: pinhole viewing, assumed to remove blur cues from the cue-integration process, still produced the pattern observed in control conditions in which a texture/outline cue for a shallow ridge overwhelmed stereo cues for a steep ridge. This result is against the hypothesis that perhaps blur cues for the stereogram projection surface differentially favoured the shallow texture/outline cues. A new variant of the blur-cue hypothesis is offered to account for this result. The main conclusion from the study is: beware drawing firm conclusions from stereograms about the pattern of cue integration that can be expected when real objects are being viewed. The two situations can produce very different results as far as cue integration is concerned. This is a conclusion with serious implications for the use of stereograms for studying the integration of stereo with other cues.
Binocular Correspondence and Visual Direction
Authors: van de Grind Wim A , Erkelens Casper J , Laan Alfons C
Published: January 2007

Two classic theories of direction vision, one by Hering, the other by Wells, are expressed in mathematical form and compared. The Hering disparity field differs considerably from the Wells disparity field, but if both are scaled for the change of acuity with eccentricity their differences are much more subtle. This explains why it is hard to determine which theory predicts direction perception best, although the tests favour Hering's theory. It is proved that Wells's construction (his rule 3) follows directly from his first two rules and Aguillonius's assumption that the horopter in the fixation plane is a frontoparallel line. Wells's theory is clearly outdated and does not mesh well with modern three-dimensional geometry of binocular vision, which Hering's theory does. Moreover, Wells inextricably mixes distance and direction vision right from the start, whereas Hering properly treats the two-dimensional manifold of directions and the depth-gauging principles separately. The use of terms such as ‘Wells—Hering’ rules should be discouraged and both Wells and Hering should be remembered separately for their clearly distinct and independent contributions. The work of Hering is still relevant to modern theory and praxis of binocular vision. The extension of Hering's approach to vertical disparities is treated for stimuli in frontoparallel planes. It is shown that acuity-scaled vertical-disparity information sampled at a single glance is below resolution beyond about arm's length. It can only be used if eye movements are allowed. Throughout, the simplest derivations of the geometrical relations that it was possible to find are given, so that the review of binocular geometry might also be of some didactical use. Finally it is indicated in which direction it might be necessary to modernise the concept of binocular correspondence.
A Restatement and Modification of Wells-Hering's Laws of Visual Direction
Authors: Ono Hiroshi , Mapp Alistair P
Published: January 2007

The laws of visual direction proposed by Wells some 200 years ago and Hering over 100 years ago are restated as three laws with the terminology of these two pioneers. This restatement serves both to honour their work and to strengthen some of the weaknesses in their original treatises. Second, two simple experiments, or tests of the laws, which the readers can readily perform by using their fingers as stimuli, are illustrated. Third, one of the three laws is modified to incorporate recent findings. Fourth, two recent experiments relevant to these new laws are described briefly, and their theoretical and methodological implications are discussed.
The Influence of Visual Cues on the Localisation of Circular Auditory Motion
Authors: Lakatos Stephen
Published: January 2007

A relative inability of listeners to refer auditory motion properly to the front hemifield when a rapid circular trajectory is traced around them in the horizontal plane was investigated. It was hypothesised that the representations of visual space and auditory frontal space are linked in such a way that auditory cues alone are insufficient to determine the veridical path in the front hemifield when both the front and the rear hemifield receive circular auditory input in rapid sequence. Listeners discriminated the direction of a rapid apparent trajectory created by the sequential activation of various combinations of loudspeakers and light-emitting diodes spaced evenly in a circular array. The addition of visual stimuli to the front hemifield, even when lacking motional cues, improved discrimination significantly. Conversely, when the same portion of the trajectory presented to the front hemifield consisted only of visual stimuli, performance decreased markedly. Additional conditions, in which the trajectory was restricted to a 120 deg path in the frontal plane, confirmed these effects. The findings suggest that the presence of a visual cue enhances the perception of auditory directionality, even when it does not itself provide any motion information.
The Orthogonal Orientation Shift and Spatial Filtering
Authors: Morgan Michael J , Medford Andrew , Newsome Philip
Published: January 2007

A line abutting two tilted flanks is apparently shifted towards the orientation orthogonal to the flanks and at the same time is reduced in its apparent length. It has been suggested that both effects are caused by band-pass spatial filtering, followed by location of the end points of the line at the peaks in the filtered image. Here implications of the filtering explanation of these effects are explored further. In the first experiment, it was predicted that orientation thresholds (as opposed to biases) would be increased for short line lengths, and would be further increased by abutting bars. The predictions were confirmed. It was shown in experiment 2 that the orientation shift was reduced by a small (4 min arc) gap between target lines and orthogonal flanks. In experiment 3 the threshold elevations and the orientation shift produced by orthogonal and tilted flanks were compared. Last, in experiment 4, the threshold elevations and orientation shift produced by orthogonal and tilted flanks, at different retinal eccentricities varying from 0 to 3.2 deg were compared, and the prediction that the magnitude of the orientation shift would decrease with line length and increase with eccentricity was confirmed. The connection is explored between the orientation shift and the Zöllner illusion, and demonstrations are presented of the Zöllner effect in which target and inducing lines are of opposite contrast on a gray background. It is concluded that the Judd and Zöllner illusions do not depend upon a single mechanism.
Temporal-Signal Detection and Individual Differences in Timing
Authors: Brown Scott W , Newcomb Damon C , Kahrl Kathleen G
Published: January 2007

Signal-detection procedures were used in three experiments to examine sensitivity and bias in time judgments and to evaluate individual differences in timing. The task required subjects to judge whether visual stimuli were presented for a certain target duration (the ‘signal’) or for a slightly longer duration. In experiment 1, subjects performed versions of the task involving both short (2 s) and long (12 s) target stimuli. Analyses of sensitivity and bias measures ( d' and β) provided evidence for consistency in timing performance within individuals. In experiment 2, subjects were tested on a detection task with 5, 10, or 15 s targets, followed by a temporal-reproduction task involving stimulus durations ranging from 3 to 17 s. Subjects with high temporal sensitivity showed less error in their reproductions than subjects with low temporal sensitivity. In experiment 3, subjects were pretested on a detection task with a 12 s target and then performed a temporal-production task where they attempted to generate a series of 12 s intervals under either control or informational feedback conditions. Feedback improved accuracy and reduced variability in temporal productions. However, the low-temporal-sensitivity subjects were more variable in their responses under both conditions than were the high-sensitivity subjects. The results point to the utility of a temporal-signal-detection task both as a means for studying individual differences in timing and as a pretesting technique for assigning subjects to high-sensitivity and low-sensitivity groups to reduce error in time-judgment data.
Perception of Simple and Complex Visual Stimuli: Decision Strategies and Hemispheric Differences in Same—Different Judgments
Authors: Irwin R John , Francis Margaret A
Published: January 2007

The accuracy with which observers could judge whether two visual stimuli were the same or different was measured with the rating method of detection theory. For judgments of whether two pictures referred to natural or manufactured things, the shape of the obtained receiver operating characteristic (ROC) was consistent with the observers adopting an optimal decision strategy. A similar result was found for judgments of complex but meaningless visual patterns. For judgments of whether two colours that differed along a simple sensory dimension were the same or different, however, the resulting ROC was consistent with the observers adopting a suboptimal differencing strategy. The accuracy of the judgments did not depend on the visual field to which the stimuli were presented.
Vision Comes to Mind
Authors: Cogan Alexander I
Published: January 2007

An overview is presented in which visual awareness is regarded as the epitome of the general mind—body problem. An experimental solution of the problem is considered first, followed by a philosophical outlook. It is argued that the scientific approach may eventually discover the neural correlate of visual awareness, but visual perceptions, even simple qualia like ‘brightness’ or ‘color’, occur in the mind of a conscious observer and are not reducible to observable activity of a specific set of neurons in the brain.
The Visual Discrimination of Relative Surface Orientation
Authors: Todd James T , Norman J Farley
Published: January 2007

In a series of three experiments, observers‘ discrimination thresholds for relative surface orientation were measured under full cue conditions, in which surfaces were specified by multiple sources of optical information including shading, texture, motion, and binocular disparity. The results revealed that observers’ sensitivity to relative surface orientation varies for different types of structural configuration. Weber fractions were approximately 8% for planar patches connected to form a dihedral angle. They increased to 11% for planar patches that were spatially separated, and jumped to over 26% for patches that were part of a smoothly curved surface.
All That Glitters: A Review of Psychological Research on the Aesthetics of the Golden Section
Authors: Green Christopher D
Published: January 2007

Since at least the time of the Ancient Greeks, scholars have argued about whether the golden section—a number approximately equal to 0.618—holds the key to the secret of beauty. Empirical investigations of the aesthetic properties of the golden section date back to the very origins of scientific psychology itself, the first studies being conducted by Fechner in the 1860s. In this paper historical and contemporary issues are reviewed with regard to the alleged aesthetic properties of the golden section. In the introductory section the most important mathematical occurrences of the golden section are described. As well, brief reference is made to research on natural occurrences of the golden section, and to ancient and medieval knowledge and application of the golden section, primarily in art and architecture. Two major sections then discuss and critically examine empirical studies of the putative aesthetic properties of the golden section dating from the mid-19th century up to the 1950s, and the empirical work of the last three decades, respectively. It is concluded that there seems to be, in fact, real psychological effects associated with the golden section, but that they are relatively sensitive to careless methodological practices.
You Can Tell by the Nose—Judging Sex from an Isolated Facial Feature
Authors: Chronicle Edward P , Chan Mei-Yin , Hawkings Charlotte , Mason Karen , Smethurst Kathryn , Stallybrass Kate , Westrope Kathryn , Wright Katie
Published: January 2007

Measurements taken from the nose are among the most important physical variables which discriminate statistically between male and female faces, yet several investigators have claimed that it is difficult to judge sex on the basis of noses presented in isolation. Previous work on the isolated nose has, however, involved the use of frontal views only, which may have obscured important physical differences between the noses of males and females. An investigation of the accuracy of judgments of the sex of isolated noses observed in frontal, profile, and three-quarter views by male and female subjects is reported. Judgment of sex was performed significantly more accurately than chance in all cases except for frontal views of female noses, where judgment was significantly less accurate than chance. Analysis of variance demonstrated a significant interaction of sex of nose and view of nose, such that male noses were identified better in frontal and in profile views, but female noses better in the three-quarter view. It is suggested that one possible reason for the seemingly contradictory role of the nose in previous studies of sex judgment is that all noses look more male in frontal views. For a nose to be perceived as female, its distinctive shape must be made available to the perceiver; this is most likely from the three-quarter view.
Is the Richness of Our Visual World an Illusion? Transsaccadic Memory for Complex Scenes
Authors: Blackmore Susan J , Brelstaff Gavin , Nelson Kay , Trościanko Tom
Published: January 2007

Our construction of a stable visual world, despite the presence of saccades, is discussed. A computer-graphics method was used to explore transsaccadic memory for complex images. Images of real-life scenes were presented under four conditions: they stayed still or moved in an unpredictable direction (forcing an eye movement), while simultaneously changing or staying the same. Changes were the appearance, disappearance, or rotation of an object in the scene. Subjects detected the changes easily when the image did not move but when it moved their performance fell to chance. A grey-out period was introduced to mimic that which occurs during a saccade. This also reduced performance but not to chance levels.

These results reveal the poverty of transsaccadic memory for real-life complex scenes. They are discussed with respect to Dennett's view that much less information is available in vision than our subjective impression leads us to believe. Our stable visual world may be constructed out of a brief retinal image and a very sketchy, higher-level representation along with a pop-out mechanism to redirect attention. The richness of our visual world is, to this extent, an illusion.
Duration Illusions in a Train of Visual Stimuli
Authors: Rose David , Summers Joanna
Published: January 2007

The first stimulus in a sequential train of identical flashes of light appears to last longer than those in the middle of the train. Four flashes (each 600 or 667 ms) were presented and the first was shortened until it appeared to have the same duration as that of the next. The duration of the first stimulus was found to be overestimated by about 50%. The illusion was unaffected by stimulus contrast, size, or interflash interval (between 100 and 600 ms). For some subjects, the last stimulus in the train also appeared to be about 50% longer than the penultimate flash. The results are discussed in terms of theories of how attention, arousal, and stimulus processing can affect duration perception. The mechanisms activated are peculiar to the visual system, since no similar illusion of duration was consistently experienced with a train of auditory tones.
Second-Order Texture Contrast Resolves Ambiguous Apparent Motion
Authors: Mather George , Anstis Stuart
Published: January 2007

When a black and a white square on a grey surround exchange places, it was previously shown that on a dark surround it is the white square, and on a light surround it is the black square, that is seen in apparent motion (AM). Thus the higher-contrast square carries the AM. We now show that the same is true for second-order AM of texture-defined squares. Squares were defined by four different textures: by anisotropy (horizontal versus vertical random dashes), by alphanumeric letters, by hash marks, or by dot size. The result was that the square that differed more from the surround in texture properties carried the second-order AM. Judgments of texture salience revealed a high correlation between salience and apparent motion. In a third experiment, crossover AM between dissimilar textures was investigated, and it was found that the more salient textures carried the AM. Results cannot be explained by the concept of ‘texture activity’, but instead indicate that the system extracts a measure of ‘texture contrast’ prior to analysis of salience and apparent motion.
Is Judging Time-to-Contact Based on ‘Tau’?
Authors: Smeets Jeroen B J , Brenner Eli , Trébuchet Sonia , Mestre Daniel R
Published: January 2007

An investigation was undertaken into whether judgments of time-to-contact between a laterally moving object and a bar are based on the direct perception of an optical variable (tau), or on the ratio between the perceived distance and perceived velocity of the object. A moving background was used to induce changes in the perceived velocities without changing the optical variables that specify time-to-contact. Background motion induced large systematic errors in the estimated time-to-contact. It is concluded that the judgment of time-to-contact is primarily based on the ratio between the perceived distance and the perceived velocity, and not on tau.
The Aftereffect to Relative Motion Does Not Show Interocular Transfer
Authors: Symons Lawrence A , Pearson Pauline M , Timney Brian
Published: January 2007

The motion aftereffect is strongest after viewing a moving field embedded in a patterned stationary surround, which suggests that relative motion is an important signal for its generation. The contribution of relative motion to binocular aspects of the motion aftereffect was assessed. Subjects viewed uniformly moving random dots surrounded by a stationary random-dot annulus. These displays could be presented in a variety of combinations to each eye separately or to both eyes, during adaptation and test. It was found that, although the presence of relative motion during adaptation significantly extended the duration of the monocular motion aftereffect, it did not augment interocular transfer. The presence of stationary surround contours in the nonadapting eye did not influence the aftereffect in the adapting eye. The enhancement provided by stationary surround contours is largely dependent on their presence during adaptation. The presence or absence of surround contours during the test phase did not influence the duration of the aftereffect. These findings are consistent with previous suggestions that the motion aftereffect is, in part, the result of adaptation to relative motion that occurs relatively early in the visual pathway—before binocular integration.
Gratings That Induce Perceptual Distortions Mask Superimposed Targets
Authors: Chronicle Edward , Wilkins Arnold J
Published: January 2007

Masking is known to depend upon the relationship between the spatial-frequency content of target and mask. This relationship has been held constant in three experiments in order to investigate the separate contribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg−1 (experiment 1) and a duty cycle of 50% (experiment 3). In experiment 2, the thresholds were strongly affected by the size of the background grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was linearly related to the area of visual cortex to which the grating projected. The spatial parameters of gratings that maximise masking are therefore the same as those that have been shown to be optimal for the induction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.
Surface Gradients, Contours and the Perception of Surface Attitude in Images of Complex Scenes
Authors: Christou Chris , Koenderink Jan J , van Doorn Andrea J
Published: January 2007

Sophisticated computer graphics were used to generate images of three-dimensional blocks-world scenes to investigate the perception of surface attitude. Three types of surface primitive (planar blocks, cylinders, and ellipsoids) were combined to form structured settings. The experiments were designed to investigate whether surface-based information such as gradients in shading and texture provide any significant advantage in attitude judgments over information derived from object contours. Images of shaded, textured, and line-drawn surfaces formed the stimulus set. The subjects' task consisted of setting an attitude probe on different parts of the scene so that the probe appeared to be locally coplanar with the perceived surfaces.

Analysis of settings according to attitude components, slant and tilt, shows remarkable agreement in slant settings for the shaded and line-drawn scenes but poor correlation between shaded and textured scenes. Similarly, tilt was also easily judged in shaded and line-drawn scenes and the experiments indicate that explicit surface boundaries are important for stable tilt perception. In general, the results suggest that, for the simple surfaces employed here, surface cues provide little extra information beyond that which is derived from contours.
The Role of the Angle Components in the Wings-in and Wings-out Forms of the Müller-Lyer Illusion
Authors: Predebon John
Published: January 2007

The effect of selective amputations of the angle components in the wings-in (underestimated) and wings-out (overestimated) forms of the Müller-Lyer illusion was examined in two experiments. The stimulus figures consisted of one, two, or four angles. In experiment 1 the method of paired comparisons was used to scale the figures on the psychological continuum of length, and in experiment 2 the method of reproduction was used to obtain quantitative measures of illusion magnitude. There was good agreement between the scaling and the length-reproduction measures of the illusion. The illusory effects in all figures were significant, and the extent of the underestimation and overestimation of the wings-in and wings-out figures, respectively, increased as the number of angles increased. In general, selective amputation of the angle components produced similar patterns of illusory effects in the wings-in and wings-out figures. These findings are discussed with reference to the issue of whether the two forms of the conventional (ie four-angle) Müller-Lyer illusion are similar or distinct illusion types.
Interactions of Monocular and Cyclopean Components and the Role of Depth in the Ebbinghaus Illusion
Authors: Papathomas Thomas V , Feher Akos , Julesz Bela , Zeevi Yehoshua
Published: January 2007

A study of size interactions of objects in three-dimensional space is reported. The canonical form of the Ebbinghaus illusion—test circles surrounded by large or small inducers—was used. Both monocularly visible (M) and purely cyclopean (C) objects were displayed stereoscopically to isolate the monocular and cyclopean components of the illusion. The results of two experiments indicate that: (i) depth plays a significant role when the test circles are cyclopean, but not when they are monocularly visible; and (ii) the size of C objects is affected equally by C and M inducers, but the size of M objects is affected much more strongly by M than by C inducers. In conclusion, possible explanations are offered for the main trends in the data, the most interesting of which is that cyclopean tests seem to be interacting only with the cyclopean component of monocularly visible inducers.
‘Generic-View Principle’ for Three-Dimensional-Motion Perception: Optics and Inverse Optics of a Moving Straight Bar
Authors: Kitazaki Michiteru , Shimojo Shinsuke
Published: January 2007

The generic-view principle (GVP) states that given a 2-D image the visual system interprets it as a generic view of a 3-D scene when possible. The GVP was applied to 3-D-motion perception to show how the visual system decomposes retinal image motion into three components of 3-D motion: stretch/shrinkage, rotation, and translation. First, the optical process of retinal image motion was analyzed, and predictions were made based on the GVP in the inverse-optical process. Then experiments were conducted in which the subject judged perception of stretch/shrinkage, rotation in depth, and translation in depth for a moving bar stimulus. Retinal-image parameters—2-D stretch/shrinkage, 2-D rotation, and 2-D translation—were manipulated categorically and exhaustively. The results were highly consistent with the predictions. The GVP seems to offer a broad and general framework for understanding the ambiguity-solving process in motion perception. Its relationship to other constraints such as that of rigidity is discussed.
Comments on Parks's “Prior Experience of Form and Illusory Figures: New Demonstrations”
Authors: Wenderoth Peter
Published: January 2007

Parks presented two example figures to illustrate that (i) familiarity can enhance illusory contour effects by completing an otherwise incomplete form and (ii) such contours are enhanced when their presence can explain an otherwise familiar but incomplete form. While familiarity probably does enhance illusory contours, additional perceptual factors may be involved in Parks's demonstrations.
Effect of Size and Frame of Visual Field on the Accuracy of an Aiming Movement
Authors: Coello Yann , Grealy Madeleine A
Published: January 2007

The aim of this study was to analyse the effects of manipulating the size and contour of the visual field on the accuracy of an aiming task. Subjects were required to perform pointing movements without seeing their moving hand. The target was displayed in either a wide structured visual field (control condition), a narrow visual field with orthogonal frame, or a narrow visual field with circular frame. The visual information surrounding the target was always provided prior to movement onset, but during the execution of the movement on only half of the trials. Overall, the results showed that undershooting was a common performance characteristic in all of the conditions. In comparison to the control performance, an increase of the degree of undershoot was found when the target was displayed inside a narrower visual field. An additional radial error was found when the contour of the visual scene was circular, but only when the visual context was available during the movement. The same pattern of results was observed for variable error. However, angular errors were not found to vary over the different conditions. Overall, the findings suggested that the visual context contributed to the assessment of the target locations, and the subsequent motor programming. Furthermore, visual information aided the on-line control of the unseen hand, but the extent of this was dependent on the size and shape of the frame denoting the visual scene. Finally, in the absence of any unexpected perturbation, the en-route amendment of the arm trajectory, based on visual information processing, seemed to be more related to distance than azimuth control.
Global Precedence in Visual Search? Not So Fast: Evidence Instead for an Oblique Effect
Authors: Durgin Frank H , Wolfe Sarah E
Published: January 2007

The evidence from an earlier report of global precedence in visual search is reexamined. Two new experiments are reported. The results of the first experiment indicate that the confusability of oblique orientations (a class-2 oblique effect) rather than global precedence was responsible for the earlier results. The results of the second experiment show that the effect critically depends on the presence of heterogeneous distractors rather than on differences in raw processing speed for different spatial scales. The possible role of symmetry is discussed.
Induced Effects of Backgrounds and Foregrounds in Three-Dimensional Configurations: The Role of T-Junctions
Authors: Zaidi Qasim , Spehar Branka , Shy Michael
Published: January 2007

In three-dimensional configurations, and two-dimensional pictures of such configurations, simultaneous contrast induction from proximate backgrounds affects perceived brightness, color, and internal contrast to a greater extent than induction from coplanar or occluding surrounds or from more distant backgrounds. In the projected image the presence of occluding flanks or retinally adjacent distant backgrounds is indicated by T-junctions. However, the presence of T-junctions inhibits induced contrast irrespective of the three-dimensional percept. The configurations in this paper refute the notions that perceived coplanarity or perceptual belonging necessarily enhance induced contrast.
An Account of Brightness in Complex Scenes Based on Inferred Illumination
Authors: Schirillo James A , Shevell Steven K
Published: January 2007

Achromatic brightness matches between two small patches were measured in a display containing ten larger regions of different luminances. The spatial organization of the ten regions was varied while keeping constant the immediate surround (and thus local contrast) of each patch as well as the average luminance of the entire stimulus. Various spatial arrangements were designed to alter the illumination inferred by the observer without changing the ensemble of luminances actually in view. Some spatial arrangements of the ten regions were consistent with five (simulated) surfaces under two distinct levels of illumination, with one luminance edge within the display (an ‘apparent illumination edge’) dividing the stimuli into an area of lower illumination and an area of higher illumination. In other spatial arrangements the ten regions were configured so that no luminance edge in the display could be interpreted as an ecologically valid illumination edge that provides a parsimonious interpretation of the ten regions; these conditions were designed to induce observers to infer ten surfaces under a single illuminant. When the ten regions were arranged with an apparent illumination edge, the patch within the area of lower perceived illumination was perceived as dimmer than when the same patch and immediate surround were presented with no apparent illumination edge. The results are interpreted by positing that the apparent illumination edge causes an observer to group together regions under the same perceived illuminant, with a consequent effect on brightness: lowering or raising the level of a perceived illuminant causes a patch of fixed contrast to be perceived as less bright or more bright, respectively, just as occurs when lowering or raising the level of real illumination. It is suggested that changes in brightness in a complex scene that result from a change in real illumination may be caused by a difference in inferred illumination at the perceptual level, not by simply a change in the amount of light absorbed by photoreceptors.
Ambiguities in Colour Constancy and Shape from Shading
Authors: Jakobsson Torbjörn , Bergström Sten Sture , Gustafsson Karl-Arne , Fedorovskaya Elena
Published: January 2007

A new visual phenomenon—called the AMBEGUJAS phenomenon—is presented, together with some descriptive data from two initial exploratory experiments. The phenomenon is basically one of shape from shading, but ambiguous as to both shape and colour. There are two spontaneously alternating and mutually exclusive perceived 3-D shapes, and—as the most surprising observation—the colour impressions of these two shapes are markedly different. The stimulus situation is very simple with two differently coloured illuminations (with sharp edges) adjacently cast onto a flat, grey striped surface. In one 3-D shape almost the whole chromatic content disappears, and the surface goes towards its veridically grey colour. In the other the perceived object assumes the two illumination colours as clear surface colours. The decolorised percept is interpreted as a striking example of colour constancy: a perceptual solution with the classical ‘discounting of the illuminant’. Experiments show that the phenomenon is robust and appears in varying display layouts and different combinations of chromatic illuminations.
Blur and Contrast as Pictorial Depth Cues
Authors: O'Shea Robert P , Govan Donovan G , Sekuler Robert
Published: January 2007

Studies have shown that blur can act as a pictorial cue to depth perception. But blurring a stimulus reduces its contrast, and studies have also shown that contrast can act as a pictorial cue to depth perception. To determine whether blur and contrast have separate influences on depth perception, each variable was independently manipulated in two experiments. Observers reported depth alternations in a simple reversible figure. Both contrast and blur were found to influence depth perception, but blur had its greatest effect at moderate contrasts. When blurred and sharp stimuli were equated on either Michelson or RMS contrast, blur continued to affect depth perception. Hence blur can act as a depth cue independently of contrast. It is speculated that blur is effective as a pictorial cue because of its usual association with other depth cues, particularly in pictures and photographs.
Motion Extrapolation and Velocity Transposition
Authors: Sokolov Alexander N , Ehrenstein Walter H , Pavlova Marina A , Cavonius C Richard
Published: January 2007

A study of the effect of the size of a moving target and the extent of its visible motion on motion extrapolation is reported. Targets (a horizontal pair of dots separated by either 0.2 or 0.8 deg) moved across a 10 deg rectilinear path and were then occluded. Observers pressed a key when they thought the leading dot of a hidden target had reached a randomly specified position (0–12 deg from the point of occlusion). In experiment 1, in agreement with velocity-transposition predictions, at moderate (5 deg s−1) and rapid (10 deg s−1) velocities extrapolation times were longer for large targets than for small ones. At slow velocity (2.5 deg s−1) this effect was reversed. In experiment 2 the effect of target size at moderate velocity was found for a short (2.5 deg) visible path. However, the extrapolation time increased with shorter (2.5 deg versus 10 deg) paths. A proposed account of these effects suggests that the visual system performs a spatiotemporal scaling, according to the velocity-transposition principle, not only of visible motion but also of extrapolated motion.
Spatial Scale Interactions and Image Statistics
Authors: Brady Nuala
Published: January 2007

In natural scenes and other broadband images, spatial variations in luminance occur at a range of scales or frequencies. It is generally agreed that the visual image is initially represented by the activity of separate frequency-tuned channels, and this notion is supported by physiological evidence for a stage of multi-resolution filtering in early visual processing. The question whether these channels can be accessed as independent sources of information in the normal course of events is a more contentious one. In the psychophysical study of both motion and spatial vision, there are examples of tasks in which fine-scale structure dominates perception or performance and obscures information at coarser scales.

It is argued here that one important factor determining the relative salience of information from different spatial scales in broadband images is the distribution of response activity across spatial channels. The special case of natural scenes that have characteristic ‘scale-invariant’ power spectra in which image contrast is roughly constant in equal octave frequency bands is considered. A review is presented of evidence which suggests that the sensitivity of frequency-tuned filters in the visual system is matched to this image statistic, so that, on average, different channels respond with equal activity to natural scenes. Under these conditions, the visual system does appear to have independent access to information at different spatial scales and spatial scale interactions are not apparent.
The Use of Image Blur as a Depth Cue
Authors: Mather George
Published: January 2007

Images of three-dimensional scenes inevitably contain regions that are spatially blurred by differing amounts, owing to depth-of-focus limitations in the imaging apparatus. Recent perceptual data indicate that this blur variation acts as an effective cue to depth: if one image region contains sharply focused texture, and another contains blurred texture, then the two regions may be perceived at different depths, even in the absence of other depth cues. Calculations based on the optical properties of the human eye have shown that variation in blur as a function of depth follows the same course as variation in binocular disparity with depth. Computational modelling has shown that the effect of blur on single-step edges is very similar to its effect on random fractal patterns, because the two stimuli have similar Fourier amplitude spectra. Blur discrimination thresholds for the two stimuli were also very similar, and could be predicted by a model based on high-spatial-frequency discrimination. A comparison of blur discrimination thresholds with the range of binocular stereopsis indicates that blur and disparity cues cover different distance ranges: stereopsis is most effective for distances relatively close to fixation, while blur information should be more effective for larger distances.
Spatial Scale and Saccade Programming
Authors: Findlay John M , Gilchrist Iain D
Published: January 2007

The global effect in eye orienting occurs when saccades land at the ‘centre of gravity’ of a target stimulus configuration. Short-latency saccades are particularly prone to this effect whereas longer-latency saccades may show more influence of fine detail. Alternative explanations of these effects are considered and data are presented from an experiment in which the influence of different stimulus features on the global effect in a search task was examined. The effect shows a substantially different time course for target-distractor combinations differing in contrast polarity (black vs white) than for combinations differing in shape (circle vs square). It is concluded that the global effect cannot be explained either as a high-level strategic effect or as an effect of automatic fast processing of low-spatial-frequency information in early sensory channels. Instead it is suggested that the visual-spatial-integration characteristic of the global effect is an integral and unavoidable part of the process of selection of saccadic response.
Integration of Physical and Semantic Information in Object Processing
Authors: Boucart Muriel , Humphreys Glyn W
Published: January 2007

Physiological studies report independent processing pathways for form and colour information. A more-complex picture on human subjects has previously been reported. A sequential matching task was used that was based on a physical property of an object and in which semantic relations between stimuli were manipulated. Performance was affected by semantic information when matching was based on a property of the form of an object (its orientation, shape, or size). Effects of semantic information were eliminated when matching was based on the colour of a local part of an object but were found again when subjects matched pictures on the basis of the percentage of a colour integrated across the shape boundary. The results suggest independent selection mechanisms in vision in which selection by local colour can be based on inhibition of the form-processing pathway whilst processing of the global configuration of the form of an object activates automatically the identification process.
Depth Interactions between Inclined and Slanted Surfaces in Vertical and Horizontal Orientations
Authors: Pierce Byron J , Howard Ian P , Feresin Catina
Published: January 2007

Depth interactions between a frontal test surface and an adjacent induction surface were measured as a function of the type of disparity in the induction surface and of the vertical/horizontal orientation of the boundary between the surfaces. The types of disparity were 4° horizontal-shear disparity, 4° vertical-shear disparity, and 4° rotation disparity; 4% horizontal-size disparity, 4% vertical-size disparity, and 4% overall-size disparity. Depth contrast in a frontal surface was produced by surfaces containing horizontal-size disparity but not by those containing horizontal-shear disparity. Vertical-shear and vertical-size disparities produced induced effects in both the induction and the test surface, which is here explained in terms of deformation-disparity processing. Effects of rotation disparity on the test surface can be accounted for in terms of cyclovergence, deformation disparity, and perhaps also depth contrast. The fact that horizontal-size disparity produced more depth contrast than horizontal-shear disparity is due to an anisotropy of disparity processing rather than the relative orientation of the surfaces. Ground surfaces appeared more slanted than ceiling surfaces. Surfaces containing horizontal disparities produced a sharp boundary with the test surface because horizontal disparities are processed locally. Surfaces with vertical disparities produced a gradual boundary with the test surface because vertical disparities are processed over a wider area.
The Role of Typical Contours in the Encodement of Objects in Three-Dimensional Arrays
Authors: Deręgowski Jan B , McGeorge Peter
Published: January 2007

Two experiments are reported in which the relationship between the orientation of the typical contour of a lamella in relation to the observer, and the ability of the observer to learn the correct position and orientation of sets of lamellae in three-dimensional arrays, was examined. For lamellae presented with their typical contour in a plane other than the observer's frontoparallel plane, the results of both experiments indicated that participants encoded lamellae in such a way that their typical contour appeared to be closer to the observer's frontoparallel plane than the respective stimulus. The relationship of the present findings to previous results on children's drawings and to the concept of the picture plane are considered.
Grouping by Proximity or Similarity? Competition between the Gestalt Principles in Vision
Authors: Quinlan Philip T , Wilton Richard N
Published: January 2007

The nature of the psychological processes that underlie the Gestalt principles of grouping by proximity and grouping by similarity is examined. Similarity was defined relative to the principles of grouping by common colour and grouping by common shape. Subjects were presented with displays comprising a row of seven coloured shapes and were asked to rate the degree to which the central target shape grouped with either the right or the left flanking shapes. Across the displays the proximal and featural relationships between the target and flankers were varied.

These ratings reflected persuasive effects of grouping by proximity and common colour; there was only weak evidence for grouping by common shape. Nevertheless, both common colour and common shape were shown to override grouping by proximity, under certain conditions. The data also show that to understand how the Gestalt principles operate it appears necessary to consider processes that operate within and between groups of elements that are initially identified on the basis of proximity. Whether such groups survive further analysis depends critically on the featural content of the constituent elements.