THE EFFECT OF STIMULUS SIZE ON HUMAN CORTICAL POTENTIALS-EVOKED BY CHROMATIC PATTERNS

The effect of stimulus size on the pattern onset-offset visual evoked potential elicited with stimuli of two different wavelengths is studie d under intensive yellow adaptation: (1) The onset response obtained w ith a 460 nm pattern is of negative polarity (N1) and saturates in amp litude with a stimulus radius of 7 deg. The onset response obtained wi th a 550 nm pattern is of positive polarity and continues to increase up to the maximum size (32.2 deg). (2) The peak time of N1 (460 nm) de creases with increasing stimulus size, that of P1 (550 nm) remains con stant. These results are discussed as reflecting either varying retina l and brain anatomy, or cone activity, color-opponent activity, or lum inance contrast activity. (C) 1997 Elsevier Science Ltd.