Differential visual evoked cortical responses to direct and peripheral stimulation in man

Clearly defined differential summated cortical evoked responses are demonstrated for central and peripherally applied visual stimuli. Central vision is associated with a low amplitude positive peak at 75 msec and a prominent high voltage positive peak at around 100 msec; later relatively low amplitude positive peaks are generally also observed. With peripheral stimulation at 15 degrees and greater the 75 msec positive peak is accentuated; the 100 msec positive peak becomes inconspicuous, and the later positive peaks at 165 msec and greater are strongly enhanced. These data support the hypothesis that the positive peaks are the cortical responses to the differential actions of the rod and cone cell components of the retina.