Flicker fusion characteristics of rod photoreceptors in the toad.

Critical fusion frequency (CFF) of toad rods was examined at various intensities using intracellular recordings. Data were compared to CFF measurements (as a function of intensity) obtained with the electroretinogram (ERG) and with a horizontal cell. In all instances the rod (and rod mediated) responses produced a curve which increased monotonically to a high frequency asymptote at about 6 Hz. The curves obtained with the ERG and the horizontal cell were double branched. The upper branch exhibited a Purkinje shift and thus must have been produced by cones. Even when using a red background to suppress cone sensitivity, there was no sign of a second rod mediated branch in the CFF curves from this retina.