Features of the human rod bipolar cell ERG response during Fusion of Scotopic Flicker

The ability of the eye to distinguish between intermittently presented flash stimuli is a measure of the temporal resolution of vision. The aim of this study was to examine the relationship between the features of the human rod bipolar cell response (as measured from the scotopic ERG b-wave) and the psychophysically measured critical fusion frequency (CFF). Stimuli consisted of dim (∼0.04 Td • s), blue flashes presented either singly, or as flash pairs (at a range of time separations, between 5 and 300 ms). Single flashes of double intensity (∼0.08 Td • s) were also presented as a reference. Visual responses to flash pairs were measured via (1) recording of the ERG b-wave, and (2) threshold determinations of the CFF using a twoalternative forced-choice method (flicker vs. fused illumination). The results of this experiment suggest that b-wave responses to flash pairs separated by <100 ms are electrophysiologically similar to those obtained with single flashes of double intensity. Psychophysically, the percepts of flash pairs <100 ms apart appeared fused. In conclusion, the visual system's ability to discriminate between scotopic stimuli may be determined by the response characteristics of the rod bipolar cell, or perhaps by the rod photoreceptor itself.