UC San Diego

Lateral interactions between visual stimuli were studied using luminance patterns that consisted of a low-contrast "center" and a high-contrast "surround" Contrast threshold for a center stimulus was measured in the presence of two surround stimuli. In a map of sensitivity changes created in the center by the surround, we found focal areas of sensitivity increments: facilitatory "islands" whose positions in the maps depended on the spatial frequency and contrast of the surround stimuli. Numerical modeling of the center-surround interactions suggested that such islands could only arise in a nonlinear system. By replacing the spatially extended center stimulus with a localized stimulus, we found that this nonlinearity is likely to have a sensory source rather than be associated with making sensory decisions. We complete this study by mapping the neural "field" created by the surround across spatial location and by studying how properties of the field depends on properties of the surround