A stereoscopic view of visual processing streams.

Recent anatomical and physiological studies of the visual pathway suggest the existence of at least three parallel processing streams in the lateral geniculate/primary cortex structure--a magno/interblob stream for motion and transient information; a parvo/interblob stream for high spatial frequency, static information; and a parvo/blob stream for chromatic and low spatial frequency information. How does this functional typology relate to the processing for stereoscopic depth? Human stereopsis may be viewed as consisting of three distinct types of disparity processing: coarse, local stereopsis suitable for stereomovement processing by the magno/interblob stream; fine, global stereopsis suitable for the processing of complex random-dot stereograms by the parvo/interblob stream; and simple, protostereopsis for processing size differences between the two eyes by the parvo/blob stream. Extensive psychophysical evidence supports the identification of these three disparity processes with the three processing streams.