Size specificity and interocular suppression: Monocular evoked potentials and reaction times

Abstract

Changes in visual evoked potentials (VEPs) and reaction time (RT) to checkerboards flashed to the left eye were investigated as a function of the size of checks in checkerboards continuously viewed by the right eye. The checkerboards, ranging in check size from 9′ to 95′ of arc, were presented to corresponding retinal areas by means of a haploscope. The results indicated that continuous stimulation of one eye suppressed VEP amplitude in response to flashing the other eye. The interocular suppression was size specific: VEP amplitude became progressively smaller as the check size of the suppressing stimulus approached that of the test stimulus (12′ or 35′ of arc) and was smallest when both eyes were stimulated by the same check size. Interocular suppression was reflected to a lesser degree in the RT data. The results are consistent with the hypotheses that there are binocularly innervated size-specific channels located central to the optic chiasm and that saturation of such a channel by continuous stimulation of one eye, with the appropriate check size, will occlude responsivity of that channel to transient stimulation of the other eye.