We studied the relation between anatomical structure and functional properties of cells in area V2 of the macaque. Visual function was assessed in the alert animal during fixation of gaze. Recording sites were reconstructed with respect to cortical lamination and the cytochrome oxidase pattern. We measured orientation and direction selectivity, end-stopping, sensitivity to binocular disparity and ocular dominance, and determined more complex functions like sensitivity to anomalous contours and lines defined by coherent motion. Orientation selectivity was found in all parts of area V2, with high frequencies in the pale and thick stripes of the cytochrome oxidase pattern, and with lower frequency in the thin stripes. Representations of anomalous contours were found in the pale and thick stripes with similar frequencies, but generally not in the thin stripes, which have been thought to process colour. Lines defined by coherent motion were most frequently represented in the thick stripes; they were less frequent in the pale stripes, and (as with anomalous contours) were not found in the thin stripes. Sensitivity to binocular disparity was found in all types of stripes, but more frequently in the thick stripes, where the exclusively binocular neurons were also concentrated. By contrast, no segregation was found for direction selectivity and end-stopping. All neuronal properties were distributed evenly across cortical laminae. We conclude that mechanisms for figure-ground segregation involve the pale and the thick stripes of the cytochrome oxidase pattern, perhaps with greater emphasis on 'shape from motion' and 'stereoscopic depth' in the thick stripes, while more elementary neuronal properties are distributed almost evenly across the stripe pattern.

Functional Organization of Area V2 in the Alert Macaque

Subjective contours, tilt aftereffects, and visual cortical organization

Human visual perception is a fundamentally relational process: Lightness perception depends on luminance ratios, and depth perception depends on occlusion (difference of depth) cues. Neurons in low-level visual cortex are sensitive to the difference (but not the value itself) of signals, and these differences have to be used to reconstruct the input. This process can be regarded as a 2-dimensional differentiation and integration process: First, differentiated signals for depth and lightness are created at an earlier stage of visual processing and then 2-dimensionally integrated at a later stage to construct surfaces. The subjective filling in of physically missing parts of input images (completion) can be explained as a property that emerges from this surface construction process. This approach is implemented in a computational model, called DISC (Differentiation-Integration for Surface Completion). In the DISC model, border ownership (the depth order at borderlines) is computed based on local occlusion cues (L- and T-junctions) and the distribution of borderlines. Two-dimensional integration is then applied to construct surfaces in the depth domain, and lightness values are in turn modified by these depth measurements. Illusory percepts emerge through the surface-construction process with the development of illusory border ownership and through the interaction between depth and lightness perception. The DISC model not only produces a central surface with the correctly modified lightness values of the original Kanizsa figure but also responds to variations of this figure such that it can distinguish between illusory and nonillusory configurations in a manner that is consistent with human perception.

/pdf/surface-construction-by-a-2-d-differentiation-integration-4k44m8nxti.pdf

Surface construction by a 2-D differentiation-integration process: a neurocomputational model for perceived border ownership, depth, and lightness in Kanizsa figures.

Subjective contours are characterized by both the appearance of an illusory border and an increase in apparent brightness within the illusory border. Theories have typically addressed only one of these perceptual attributes. The present experiments measured both apparent brightness and apparent border sharpness of stimuli that varied parametrically in number and width of inducing elements and stimulus configuration. It was found that apparent brightness is influenced more by number of inducing elements, whereas apparent sharpness increases more with inducing element width. Stimulus configuration may influence brightness and sharpness differentially. Thus, to be complete, theoretical accounts of subjective contours must address both perceptual attributes.

/pdf/stimulus-determinants-of-brightness-and-distinctness-of-3f0mq09sg8.pdf

Stimulus determinants of brightness and distinctness of subjective contours.

Illusory figures: a (mostly) atheoretical review

The possibility that subjective contours are an artifact of brightness contrast was explored. In one experiment, inducing luminance was found to have different effects on the clarity of subjective contours and the magnitude of brightness contrast. The results of a second experiment indicated that differences of luminance in a stimulus display are necessary for subjective contours to be sustained, whereas chromatic differences are not. It is concluded that subjective contour and brightness contrast are distinct perceptual phenomena but share a dependency on the processing of edge information transmitted through the achromatic channels of the visual system.

https://www.jstor.org/stable/info/1421648

Sensory information and subjective contour.

Magnitude estimates of target brightness and clarity were obtained in a metacontrast paradigm as a function of stimulus onset asynchrony (SOA), target and mask duration, and fixation location. Under conditions of backward masking, effects on brightness and clarity were in opposite directions at short SOAs (i.e., judgments reflecting less clarity were accompanied by judgments that indicated increases in target brightness). However, at long SOAs and under conditions of forward masking, estimates of target brightness and clarity moved in the same direction. The results are discussed in the context of the “sustained-transient” theories of visual masking, and it is concluded that, in their present forms, these theories cannot completely handle the data we have reported.

/pdf/differential-effects-of-metacontrast-on-target-brightness-4x83pevave.pdf

Differential effects of metacontrast on target brightness and clarity

Following adaptation to a rectangular grating, subjects observed a shift in the perceived duty cycle of a test grating (Burton, Nagshineh, & Ruddock, 1977; DeValois, 1977). This suggests that size information about black and white pattern components may be analyzed independently. We have tested this hypothesis by combining adaptation to a 2-cpd rectangular wave grating (narrow white bars and wide black bars or vice versa) with adaptation to a 4-cpd sine wave (narrow white and black bars. The data do not support the independent analysis of white and black components, but they may be accounted for by mechanisms sensitive to the relative phase relations among the spatial frequency components of the input.

/pdf/evidence-against-independent-processing-of-black-and-white-cvtrp40r48.pdf

Evidence against independent processing of black and white pattern features.

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Sensory information and subjective contour.

Differential effects of metacontrast on target brightness and clarity

Evidence against independent processing of black and white pattern features.