' "Mf ^ SEEING PERCEIVING '68 V BRILL Seeing and Perceiving 25 (2012) 545-560 brill.com/sp Features of the Human Rod Bipolar Cell ERG Response During Fusion of Scotopic Flicker Allison M. Cameron '^ * and Jacqueline S. C. Lam' Division of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 0200, Australia ^ ARC Centre of Excellence in Vision Science, The Australian National University, Canberra, ACT 0200, Australia ' The ANU Medical School, The Australian National University, Canberra, ACT 0200, Australia Received 19 June 2011 ; accepted 7 April 2012 Abstract 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 è-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 ¿-wave, and (2) threshold determinations of the CFF using a two- alternative forced-choice method (flicker vs. fused illumination). The results of this experiment suggest that è-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. © Koninklijke Brill NV, Leiden, 2012 Keywords Electroretinogram, retinal rod bipolar cell, flicker fusion 1. Introduction When a light stimulus is intermittently presented at a low frequency, the periods of light and darkness are perceptible as distinct visual sensations that 'flicker'. As the frequency of presentation is increased, the difference between successive sensations * To whom correspondence should be addressed. E-mail: allison.cameronl@gmail.com © Koninklijke Brill NV, Leiden. 2012 DOIilO.l 16.3/187847612X648792