The time course of interocular suppression in normal and amblyopic subjects

The authors measured the time course of interocular suppression of five normal subjects and eleven patients with amblyopia (strabismic and/or anisometropic). Orthogonal gratings were presented dichoptically for durations that ranged from 10-6000 msec. All normal observers reported fusion or superimposition of the orthogonal gratings for short stimuli and reported binocular rivalry for stimuli longer than 150 msec. At long presentation times, all amblyopes constantly suppressed the pattern that was presented to their amblyopic eye. Six amblyopes showed superimposition of the two patterns at short presentation times. Of these, three had time courses similar to those of normal observers; the other three had a much shorter onset of suppression (about 80 msec). The remaining five amblyopes perceived only the pattern of the dominant eye at short stimulus durations; at intermediate durations, they reported partial superimposition of the stimuli, whereas at the longest stimulus durations, again only the stimulus of the dominant eye was perceived. The results suggest that binocular rivalry in normal observers and strabismic suppression in amblyopes are mediated by different mechanisms. The heterogeneity of the time courses of suppression in amblyopes might result from differences in the disturbances of early visual development (age at onset of strabismus and/or anisometropia, origin, and therapy).