Interindividual variation and additivity of the visual evoked potentials to the local checkerboard stimulation of the central and paracentral retina.

Visually evoked cortical potentials to reversing checkerboard stimulation were recorded from normal subjects. Different locations of the central visual field of maximally 8 degrees radius were stimulated. Stimulation of various parts of the central visual field changed the waveform and the amplitude of the responses of different subjects very individually. This makes it impossible to make a universal decision, how large field or which part of the central field contributes most to pattern evoked cortical potentials. The responses to the upper half field stimulation showed greatest variation making the VEP recording worthless in detecting altitudinal visual field defects. The computed sum of the half field responses was of similar waveform and amplitude to the response to the full field stimulation. The good additivity of the responses applied to all parts of the central visual field tested.