Neural dynamics of brightness perception: features, boundaries, diffusion, and resonance.

Abstract

A real-time visual processing theory is used to unify the explanation of monocular and binocular brightness data. This theory describes adaptive processes which overcome limitations of the visual uptake process to synthesize informative visual representations of the external world. The brightness data include versions of the Craik-O’Brien-Cornsweet effect and its exceptions, Bergstrom’s demonstrations comparing the brightnesses of smoothly modulated and step-like luminance profiles, Hamada’s demonstrations of nonclassical differences between the perception of luminance decrements and increments, Fechner’s paradox, binocular brightness averaging, binocular brightness summation, binocular rivalry, and fading of stabilized images and ganzfelds. Familiar concepts such as spatial frequency analysis, Mach bands, and edge contrast are relevant but insufficient to explain the totality of these data. Two parallel contour-sensitive processes interact to generate the theory’s brightness, color, and form explanations. A boundary-contour process is sensitive to the orientation and amount of contrast but not to the direction of contrast in scenic edges. It generates contours that form the boundaries of monocular perceptual domains. The spatial patterning of these contours is sensitive to the global configuration of scenic elements. A feature-contour process is insensitive to the orientation of contrast, but is sensitive to both the amount of contrast and to the direction of contrast in scenic edges. It triggers a diffusive filling-in reaction of featural quality within perceptual domains whose boundaries are dynamically defined by boundary contours. The boundary-contour system is hypothesized to include the hypercolumns in visual striate cortex. The feature-contour system is hypothesized to include the blobs in visual striate cortex. These preprocessed monocular activity patterns enter consciousness in the theory via a process of resonant binocular matching that is capable of selectively lifting whole monocular patterns into a binocular representation of form-and-color-in-depth. This binocular process is hypothesized to occur in area V4 of the visual pre striate cortex.