Independent Spatial-Frequency-Tuned Channels in Binocular Fusion and Rivalry

Monocular masking studies show that the visibility of a one-dimensional sinusoidal grating remains unchanged in the presence of masking noise filtered so as to contain spectral components that are at least two octaves away from the spatial frequency of the grating (Stromeyer and Julesz 1972). In the present study, random-dot stereograms were bandpass filtered in the two-dimensional Fourier domain, and masking noise of various spatial frequency bands was added to the filtered stereograms. Masking noise bands containing equally effective noise energy were selected such that their bands were either overlapping with the stereoscopic image spectrum or were two octaves distant. The first case resulted in binocular rivalry; however, in the second case stereoscopic fusion could be maintained in the presence of strong binocular rivalry owing to the masking noise. This finding indicates that spatial-frequency-tuned channels are not restricted to one-dimensional gratings but operate on two-dimensional patterns as well. Furthermore, these frequency channels are utilized in stereopsis and work independently from each other, since some of these channels can be in binocular rivalry while at the same time other channels yield fusion. The main binocular experiments are demonstrated.