Dependence of visual evoked potentials on change of stimulated retinal area associated with different pattern displacements.

An attempt was made to distinguish between the effects of the moving edges and the change in the area of stimulated retina on pattern shift visual potentials, elicited by checkerboard pattern displacements varying through 0.25, 0.50, 0.75 and full pattern reversal. Twelve healthy subjects were stimulated binocularly with a horizontally orientated pattern (whole field 17 degrees, check size 28' of visual angle). Four of them were additionally presented with a diagonally orientated pattern. Two sets of 32 averages were taken for each stimulus condition and peak-to-peak amplitudes P50-N70 and P100-N140 were measured. The change of the stimulated retinal area is a quadratic function of the diagonally orientated pattern. The change in amplitude of P50-N70 fits well with the curve of the area change, but that in the amplitude of P100-N140 does not. Each of the amplitudes also seems to have a different orientation of hypothetical dipole vectors.