| Abstract: | Measured electrophysiological analogs of visual masking by light in single retinula (photoreceptor) cells of the lateral eye of Limulus. The intensity required for a 30-msec test flash to produce a criterion response increment in the presence of a 400-msec masking flash was determined over a range of stimulus onset asynchronies. The variation of the criterion intensity with stimulus onset asynchrony yielded a masking function quite similar to that obtained in human psychophysics, which suggests that this kind of response integration occurs in the most peripheral cell and that network interactions are not needed to account for masking by light. The implication that photoreceptor dynamics alone determine masking was examined: The criterion test flash intensity increased with receptor potential increases, but the relation could best be described by a bilinear function. It is suggested that the upper limb of the bilinear function may represent receptor saturation. Results are consistent with the notion that masking by light is a special case of the increment threshold and that receptor dynamics adequately account for dynamic factors in masking by light at this level of the visual system. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) |
