COMPARISON OF THE PATTERN-REVERSAL VISUAL-EVOKED POTENTIAL MEDIATED BY SEPARATE CONE SYSTEMS

With the purpose of recording responses mediated by the 3 cone systems visual evoked potentials (VEPs) were elicited by the reversal of mono chromatic checkerboards superimposed upon strong monochromatic backgro unds (yellow, purple and blue-green). The sensitivity to light of vari ous wave lengths were measured as the reciprocal of the intensity nece ssary to elicit a VEP amplitude of 3 mu V. The spectral sensitivity cu rves based on this VEP amplitude criterion in the presence of blue-gre en, purple and yellow adaptation showed peak sensitivities in the red, the green and the blue part of the spectrum, respectively. This indic ates that the responses reflect separate modulation of the 3 different cone mechanisms. The potentials obtained with yellow adaptation diffe red from those obtained with purple and blue-green adaptation. The amp litude versus log intensity function was flatter and the latency of th e major positive peak was increased by 20-25 msec. Repeated examinatio ns of 4 subjects suggest that the method yields reliable latency measu rements of responses mediated by separate cone mechanisms.