The intensity-dependent changes of the visual evoked responses in man to patterned and blank stimulation.

The visual evoked responses (VERs) to blank and checkerboard-patterned stimuli of 6 degrees angular subtense were recorded referentially (OZ--A2) in 10 dark-adapted subjects using a range of 5.27 log units of intensity (maximum luminance = 6420 cd/m2). The mean peak latencies of the prominent positive-negative deflection of the VERs to the blank stimuli exhibit an exponential shortening with the rise of log stimulation intensity. The peak latencies of the positive-negative deflection of the VERs to the checkerboard-pattern stimulation at low and moderate intensities are by about 50 ms shorter, with the latency of the negative peak of the response to the patterned stimulation corresponding to the positive peak latency of the response to the blank stimuli. Accordingly, the VERs to both types of stimulation are of opposite polarity. With a further increase of the stimulation intensity, the latency of the negative peak of the VER to patterned stimulation gradually lengthens due to the glaring effects of the patterned stimuli. Therefore, at high stimulation intensities the VERs to both types of stimuli are of the same polarity. The mean peak-to-peak amplitudes of the VERs to both types of stimulation differ significantly at high-intensity end of the photostimulation range only, the amplitude of the VER to the patterned stimulation being higher.