Macula and periphery: their contributions to the visual evoked potentials (VEP) in humans.

An alternating checkerboard pattern subtending a visual angle of 25 min arc is capable of eliciting remarkably high amplitudes of visually evoked potentials (VEP) outside a visual angle of 2.5 degree. These contributions cannot be neglected when evaluating a VEP response obtained with a larger field of stimulation. When the retina is consecutively stimulated by concentric frame-shaped stimuli, the algebraic sum of all single cortical responses augmented the cortical response obtained when stimulating the whole field simultaneously by approximately 30%. This finding may be explained by the inhibiting interactions within the receptive field organisation of the retina.