Subject cooperation and the visual evoked response.

The effects on the visual evoked response (VER) of subject behavior, such as accuracy of fixation, stability of eye position, and degree of concentration, are poorly documented. Experiments were performed on 20 normal subjects to investigate the effects on the VER of eye movements, off-center stimulation, concentration on another task, and voluntary defocusing. It was found that there are some conditions under which a normal subject can produce an abnormal VER which could lead to misdiagnosis.