Binocular interactions in normal and anomalous binocular vision: effects of flicker.

Temporal modulation thresholds were determined for monocular viewing and for binocular viewing of stimuli presented in phase or in counterphase to each eye of observers with normal binocular vision and those lacking stereopsis. The results showed that in individuals with normal binocular vision sensitivity was much greater for in-phase than for counterphase stimulation at low temporal frequencies, but that this superiority declined at higher temporal frequencies. Averaged across frequencies, binocular sensitivity for in-phase stimulation was 40-50% higher than monocular sensitivity. In contrast, in the observers lacking stereopsis the ratios of binocular in-phase/monocular sensitivity averaged 1.02, and there were no significant differences in sensitivity to in-phase and counterphase stimulation. This failure of binocular integration at threshold does not result from differences in transmission time between the 2 eyes. However, while individuals lacking stereopsis showed an absence of binocular interaction for uniform-field flicker at threshold, they showed suprathreshold dichoptic temporal frequency masking which was similar to that found in normal persons.