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PubMed1986

A spatial property of the retino-cortical mapping.

Striate cortex topography derives from a stretching of retinal space along the optic axis. At the retina, relative distances are preserved in a mapping of retinal space onto a spherical surface in the environment. At the cortex, relative distances along visual meridia in the cortical map are preserved in a mapping of striate cortex onto an environmental conic surface whose base is in the plane of the eye. This eco-cortical relationship can be considered a reference frame through which spatial relationships at the cortex might provide information about the environment. The present analysis provides an explanation of changes in cortical magnification with visual eccentricity in the primate and a detailed three-dimensional model of striate topography for the macaque monkey. In man, a conic environmental surface is shown to be uniformly resolvable along meridia in the visual field. Finally, the implications of this analysis of the structural properties of the retino-striate pathway and visual resolution are considered in relation to depth and distance perception.

Brain Mapping↗
PubMed1987

Effect of the number of grey levels on the detectability of a simple line signal in visual noise.

The number of grey levels, G, contained in a digitized image of an external event must affect the fidelity of reproduction of that event for physical reasons. The question arises as to whether there is a separate perceptual effect of G. Three experiments are described which investigate the effect of G on the visibility of a straight-line signal in visual noise using a signal detection analysis to separate the physical and perceptual effects of G. The results show that, for the type of displays employed, and for the specific task of detection of lines in visual noise, there was no effect of G on efficiency, which suggests that G had no separate perceptual effect.

Color Perception↗
PubMed1989

Corner effect in induced hue: evidence for chromatic band-pass filters.

An experiment is described which investigates the spatial determinants of the apparent difference in hue between the central grey patches of chromatic 'H' pattern pairs, an effect similar to that first demonstrated by Wright (1969, The Measurement of Colour, Hilger, London) in coloured gratings. The hue difference is shown to be analogous to the brightness difference in achromatic 'H' patterns demonstrated by Moulden and Kingdom (1989, Vision Res. 29, 1245-1259). The origin of both effects is argued to be the presence of the corner intersections in the 'H' patterns, which are powerful stimuli for cells with circularly-symmetric, centre-surround organization. It is suggested that the results of the experiment with the chromatic 'H' patterns implicates the operation of cells with a spectrally double-opponent, rather than single-opponent receptive field organization.

Color Perception↗
PubMed1990

Effects of stimulus complexity on simple spatial discriminations.

We have extended previous measurements on the detection of a target, differentiated in orientation or magnification from a number of identical reference elements. In these new experiments, we have used more than one class of reference element from which the target must be discriminated. For example, in the case of orientation discrimination, the reference elements are of two classes, which differ from each other in orientation, but are otherwise identical. Representatives of the two classes are present in equal numbers, and the target to be detected is presented at an orientation angle different from that of either class of reference element. Data for discrimination of target magnification or orientation are given for simple geometric elements, namely lines, squares and triangles. In nearly all cases, the characteristic time required for 50% probability of target detection, T1/2, is greater with two classes of reference elements than with a single class. In nearly all cases, T1/2 values for the mixed reference elements increase with the number of reference elements, N, corresponding to discrimination by serial processing. This remains the case even when detection is parallel (T1/2 independent of N) for either class of reference element used separately. We discuss the properties of the spatial discrimination mechanisms which give rise to these responses.

Depth Perception↗
PubMed1993

Surface decomposition accompanying the perception of transparency.

At the retina, each location can have only one value of luminance or color. When transparency is perceived, however, different surface qualities can be redistributed to two or more apparently superimposed layers. The experiments described here explored the characteristics of this surface decomposition. It is shown that the surface decomposition occurs rapidly, it affects even early stages of visual processing, and it involves attributes such as texture and motion as well as color and brightness. In the first experiment, the recognition advantage for transparent overlapping digits demonstrated that the surface decomposition accompanying transparency occurs within 60 ms. In the second, the separation of overlying orthogonal grids due to surface decomposition was found to influence the strength of the McCollough effect, an effect attributed to early cortical processing. Finally, when a transparent surface appears to extend over areas that are physically identical to the background, qualities of the transparent overlay such as texture and motion, as well as color or brightness (e.g., the neon color effect) appear to spread to the illusory overlay.

Color Perception↗
PubMed1994

The interaction of depth parameters in motion integration with polar plaids.

Many parameters have been investigated as to their effect on the way in which the visual system is able to integrate different motion directions at the same visual location. Of special interest have been parameters that determine the depth relationship between surfaces, such as disparity, relative contrast, and occlusion versus transparency. The preferred stimulus for this research has been the 'plaid', usually constructed from two linear gratings. The present study concentrated not on these Cartesian plaids, but on polar plaids, made from a combination of concentric circles and radial gratings. These kinds of plaids also have a special theoretical significance: within the Lie Transformation Group approach to visual pattern processing, Cartesian and polar stimuli represent different invariances in the visual world. This study compared Cartesian, polar and hybrid plaids as to their propensity to be perceived as coherently moving stimuli. Cartesian and polar plaids were similar in terms of the effects of intersection luminance and relative contrast on coherence, polar plaids being consistently less coherent. Hybrid plaids did not usually cohere at all. Adaptation to an unambiguously coherent plaid decreased perceived coherence when tested with a bistable plaid from the same, and not from the other Lie group, i.e. there was within-group adaptation but no between-group adaptation. Polar plaids also offer the possibility of studying the influence of another depth parameter on motion integration: expansion or contraction of circular gratings, which represent motion-in-depth toward or away from the observer. This motion-in-depth was tested for interaction with disparity or relative contrast in the determination of motion integration. The results were negative under the present conditions. Thus not all depth parameters contribute equally to the determination of the stimulus depth relations affecting the motion integration process.

Depth Perception↗
PubMed2002

Illuminant estimation as cue combination.

This work briefly describes a model for illuminant estimation based on combination of candidate illuminant cues. Many of the research issues concerning cue combination in depth and shape perception translate well to the study of surface color perception. I describe and illustrate a particular experimental approach (perturbation analysis) employed in the study of depth and shape that is useful in determining whether hypothetical illuminant cues are actually used in color vision.

Color Perception↗
PubMed2004

Bayesian combination of ambiguous shape cues.

We investigate how different depth cues are combined when one cue is ambiguous. Convex and concave surfaces produce similar texture projections at large viewing distances. Our study considered unambiguous disparity information and its combination with ambiguous texture information. Specifically, we asked whether disparity and texture were processed separately, before linear combination of shape estimates, or jointly, such that disparity disambiguated the texture information. Vertical ridges of various depths were presented stereoscopically. Their texture was consistent (in terms of maximum likelihood) with both a convex and a concave ridge. Disparity was consistent with either a convex or concave ridge. In a separate experiment the stimuli were defined solely by texture (monocular viewing). Under monocular viewing observers consistently reported the convex interpretation of the texture cue. However, in stereoscopic stimuli, texture information modulated shape from disparity in a way inconsistent with simple linear combination. When disparity indicated a concave surface, a texture pattern perceived as highly convex when viewed monocularly caused the stimulus to appear more concave than a "flat" texture pattern. Our data confirm that different cues can disambiguate each other. Data from both experiments are well modeled by a Bayesian approach incorporating a prior for convexity.

Bayes Theorem↗
PubMed2004

Slant from texture and disparity cues: optimal cue combination.

How does the visual system combine information from different depth cues to estimate three-dimensional scene parameters? We tested a maximum-likelihood estimation (MLE) model of cue combination for perspective (texture) and binocular disparity cues to surface slant. By factoring the reliability of each cue into the combination process, MLE provides more reliable estimates of slant than would be available from either cue alone. We measured the reliability of each cue in isolation across a range of slants and distances using a slant-discrimination task. The reliability of the texture cue increases as |slant| increases and does not change with distance. The reliability of the disparity cue decreases as distance increases and varies with slant in a way that also depends on viewing distance. The trends in the single-cue data can be understood in terms of the information available in the retinal images and issues related to solving the binocular correspondence problem. To test the MLE model, we measured perceived slant of two-cue stimuli when disparity and texture were in conflict and the reliability of slant estimation when both cues were available. Results from the two-cue study indicate, consistent with the MLE model, that observers weight each cue according to its relative reliability: Disparity weight decreased as distance and |slant| increased. We also observed the expected improvement in slant estimation when both cues were available. With few discrepancies, our data indicate that observers combine cues in a statistically optimal fashion and thereby reduce the variance of slant estimates below that which could be achieved from either cue alone. These results are consistent with other studies that quantitatively examined the MLE model of cue combination. Thus, there is a growing empirical consensus that MLE provides a good quantitative account of cue combination and that sensory information is used in a manner that maximizes the precision of perceptual estimates.

Cues↗
PubMed2004

Perceived surface color in binocularly viewed scenes with two light sources differing in chromaticity.

We examined the effect of perceived orientation on the perceived color of matte surfaces in rendered three-dimensional scenes illuminated by a blue diffuse light and a yellow punctate light. On each trial, observers first adjusted the color of a matte test patch, placed near the center of the scene, until it appeared achromatic, and then estimated its orientation by adjusting a monocular gradient probe. The orientation of the test patch was varied from trial to trial by the experimental program, effectively varying the chromaticity of the light mixture from the two light sources that would be absorbed and reemitted by a neutral test patch. We found that observers' achromatic settings varied with perceived orientation but that observers only partially discounted orientation in making achromatic settings. We developed an equivalent illuminant model for our task in which we assumed that observers discount orientation using possibly erroneous estimates of the chromaticities of the light sources and/or their spatial distribution. We found that the observers' failures could be explained by two factors: errors in estimating the direction to the punctate light source and errors in estimating the chromaticities of the two light sources. We discuss the pattern of errors in estimating these factors across observers.

Color Perception↗
PubMed2006

Illusory spreading of watercolor.

The watercolor effect (WCE) is a phenomenon of long-range color assimilation occurring when a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour; the brighter color spreads into the entire enclosed area. Here, we determined the optimal chromatic parameters and the cone signals supporting the WCE. To that end, we quantified the effect of color assimilation using hue cancellation as a function of hue, colorimetric purity, and cone modulation of inducing contours. When the inner and outer contours had chromaticities that were in opposite directions in color space, a stronger WCE was obtained as compared with other color directions. Additionally, equal colorimetric purity between the outer and inner contours was necessary to obtain a large effect compared with conditions in which the contours differed in colorimetric purity. However, there was no further increase in the magnitude of the effect when the colorimetric purity increased beyond a value corresponding to an equal vector length between the inner and outer contours. Finally, L-M-cone-modulated WCE was perceptually stronger than S-cone-modulated WCE for our conditions. This last result demonstrates that both L-M-cone and S-cone pathways are important for watercolor spreading. Our data suggest that the WCE depends critically upon the particular spatiochromatic arrangement in the display, with the relative chromatic contrast between the inducing contours being particularly important.

Adult↗
PubMed2006

Motion from occlusion.

Vision uses specific image features or cues to infer physical properties of the world. Here, we use a novel illusion to show that occlusion, traditionally thought of as a cue to depth, is also a powerful cue to motion. A display of stacking disks that contains only occlusion as a cue to depth generates a vivid sense of movement that is likely computed in early or middle levels of visual processing.

Cues↗
PubMed1989

Auditory, visual, and multisensory nonverbal social perception in adolescents with and without learning disabilities.

Adolescents with and without learning disabilities (14, 16, and 18 years old) were tested to determine whether they differed in auditory, visual, and/or multisensory (combined auditory/visual) social perception abilities. Differences between the two groups in growth of auditory, visual, and multisensory social-perception abilities were also measured. Results of the data analyses revealed that adolescents with learning disabilities were not as adept at understanding nonverbal social information regardless of whether the information was visual or multisensory in nature. Further, nonverbal social-perception ability for both visual and multisensory information improved with increasing age for both populations. Finally, adolescents with learning disabilities continued to demonstrate comparatively poorer social-perception abilities through the 18-year level.

Adolescent↗
PubMed1980

Releasers of imprinting: instinctive preferences for liver models and those with painted sign-stimuli.

White Leghorn chicks hatched and raised in isolation were tested for their preference to situations where age-mates or silhouettes of age-mates were paired against hens, other adult animals, or silhouettes of hens with various sign-stimuli painted on. Silhouettes with painted sign-stimuli elicit quite different developmental patterns of preference, with the hens of the more complex silhouettes being prepotent. The hen silhouette models increase in prepotency when they are moving, with one exception. A Mallard drake emerged as powerful releasing object, suggesting that its large, yellow beak may be a supernormal stimulus.

Animals↗
PubMed1989

Dual attention to dynamically structured naturalistic events.

Videotapes of two naturalistic events, a basketball-like game and a vocalizing human face, were presented in a dual-task situation, with subjects responding to target events in individual episodes. The fact that the stimulus episodes consisted of natural motions permitted subjects to base their attention on the partially determinate structure that characterizes such motions. Simultaneous visual presentations were in full transparent overlap. the auditory presentations were overlapped spatially. Performance on the dual task improved significantly in all experimental conditions over two days of practice. Performance approached control-group ceiling levels for events available to different modalities (hearing and sight). When information was available only in a single modality, performance was lower over-all, but practice effects were still significant. The results are discussed in the context of a cognitive skills approach to attention.

Adult↗
PubMed1976

Evaluation of ego strength based on certain Rorschach variables.

Despite the importance of the assessment of ego strength for appropriate assignment of clients for psychotherapy and/or rehabilitation, existing techniques have not fulfilled expectations. A method for assessing ego strength through the Rorschach Test independent of clinical criterion is proposed. In addition to certain variables of Klopfer's RPRS (M+, FM+, FC+ plus CF+), sharply preceived space responses are included. They constitute a highly intercorrelated global measure of ego strength and are also highly correlated to a relatively independent Rorschach variable of global ego efficiency, i.e. integrated whole responses. In accordance with prediction, non-controlled color responses as well as accuracy of form perception did not correlate in a non-clinical sample with either measure of ego strength.

Adult↗