The research examines various phenomena of spatial interaction in human vision, including both excitatory and inhibitory interactions, in order to understand how they contribute to the perception of the spatial properties of visual stimuli. The experiments are psychophysical, but are guided by findings from the electrophysiological literature. There is special concern with the concept of tuned channels and with how spatial interactions contribute to tuning. Tuning with respect to size (size-tuning), shape (shape-tuning), and orientation (orientation- tuning) will be studied. The extent to which spatial interactions are color-coded will also be examined. The independent variables will be the spatial distribution and wavelength of light within and about the test stimulus and the exposure of various adapting stimuli prior to test observations. Dependent measures will be the abilities of subjects to detect and identify the stimuli. Adults with normal vision will serve as subjects. Illumination will be at photopic levels.