Visual evoked potentials to binocular stimulation with disparate patterns.

Experiments with VEP to checkerboard stimulation in 4 subjects with normal stereoscopic vision showed that binocular interaction was the same for fused images and for linear pattern displacement induced by horizontal and vertical prisms, as long as the patterns were projected on the macular areas of both eyes. Also in a stereo-blind subject the impaired binocular VEP interaction remained unchanged during linear displacement of the patterns. Thus the previously reported differences in binocular VEP interaction between stereo-normal stereoblind subjects cannot be explained by binocular stimulation with unfused patterns in the latter group. With patterns displaced to different hemifields in the 2 eyes, no binocular interaction was recorded. Experiments with black-and-white gratings of different orientations to the 2 eyes showed that binocular VEP reactions remained the same even with patterns perpendicular to each other. However, the binocular interaction was disrupted when the subject viewed the perpendicular patterns through coloured filters.