Stimulus alternation and fast retinal potentials: photopic anc scotopic contributions.

Human retinal oscillatory potentials in response to an alternating checker-board pattern stimulus were studied in two subjects over an intensity range of 7.5 log units. Under scotopic conditions, two wavelets (S1 and S2) could be recorded. At an intensity of 1.9 photopic log Td four high frequency oscillations (O1--O4) were noticed and a discontinuity was observed in the corresponding luminance curve of the b-wave together with a sudden decrease in the magnitude of the standard deviation of the amplitude measures. The oscillations were noticed only on the ascending slope of the b-wave. With increasing stimulus intensity, their latency decreased at a slower rate than that of the b-wave and their number decreased. Each wavelet had an amplitude maximum at a certain stimulus intensity level. It was suggested that O1--O4 were generated by the activation of the photopic system and that S1 and S2 were of scotopic origin.