Neural dynamics of form perception: boundary completion, illusory figures, and neon color spreading.

A real-time visual proces:sing theory is used to analyze real and illusory contour formation, contour and :brightness interactions, neon color spreading, complementary color induction, and filling-in of discounted illuminants and s<;otomas. The theory also physically interprets and generalizes Land's retinex theory. These phenomena are traced to adaptive processes that overcome limitations of visual uptake to synthesize informative visual representations of the external world. Two parallel contour sensitive proces:ses interact to generate the theory's br:ightness, color, and form estimates. A boundary contour process is sensitive to orientation and amount of contrast but not to direction of contrast in scenic c~dges. It synthesizes boundaries sensitive to the global configuration of scenic elernents. A feature contour process is insensitive to orientation but sensitive to both amount of contrast and to direc1:ion of contrast in scenic edges. It triggers a diffusive filling-in of featural quality within perceptual domains whose boundaries are determined by completed boundary contours. The boundary contour process is hypothesized to include (:ortical interactions initiated by hypercolumns in Area 17 of the visual cortex. The feature contour process is hypothesized to include cortical interactions initiated by the cytochrome oxydase staining blobs in Area 17. Relevant data from striate and prestriate visual cortex, including data that support two predictions, are reviewed. Implications for other perceptual theories and axioms of geometry are discus:sed.