Monocularly Evoked Cortical Potentials to Simultaneous Stimulation of Central and Peripheral Human Retina with Different Patterns

Abstract

In order to determine the relative contribution of different parts of the retina to the visually evoked cortical potential (VECP) the eye was exposed to separate, 90° phase-displaced checkerboard stimulation of central (4° in diameter) and peripheral (14° x 18°, center occluded) parts of the human retina. With high contrast central stimuli of 18 minutes of arc the VECP was always greater than the response to peripheral stimuli between 4 and 390 min of arc. With high contrast peripheral stimulation of 96 min of arc the central response to stimuli of 18 min of arc was suppressed only if the Stimulus to the central field was less than 10 per cent contrast, if the check size of the central stimulus was smaller than 6 min of arc, or if central vision was blurred to less than 0.25 visual acuity. Simultaneous phase-shifted stimuli of the central (18 min of arc) and the peripheral (96 min of arc) parts of the retina led always to a predominance of the central retina. This was not seen when the VECPs in response to separate stimulation of the central and peripheral parts of the retina were added with the aid of a computer.