Binocular summation in man and monkey

Binocular summation, using spatial and temporal modulation sensitivity measurements, has been investigated for human and rhesus monkey observers. In experiments where the refractive errors of both eyes were optimally corrected, the binocular summation functions for both species were similar in magnitude and form, and showed higher summation ratios for temporally modulated stimuli than for spatially modulated stimuli. Monocular retinal image defocus produced a reduction in binocular summation for spatial gratings with the amount of reduction dependent on both the amount of relative defocus and the spatial frequency of the stimulus grating. In contrast, monocular defocus did not effect the magnitude of binocular summation for spatial gratings with the amount for any of the conditions investigated. Over-all, the results of these investigations indicate that binocular summation measures of binocular function may have some advantages over other tests of binocular function that could be utilized in the clinical examination of patients.