Abstract

Many studies have shown interaction between the long-wavelength rod-cone mechanism and the rod mechanism. Quasi-linear additions of rod- and cone-related photic responses are most clearly implicated in the increment threshold studies of Buck, Frumkes, and MacLeod and the flicker studies of MacLeod and van den Berg, but have been suggested by a wide variety of other electrophysiological and psychophysical techniques. Quasi-linear rod-cone interactions are discerned when light flashes stimulate both rods and cones and the underlying mechanism can be understood in terms of a convergence of like polarity signals at some common neural locus. Highly nonlinear interactions between the same two spectral mechanisms have been recently and independently demonstrated by Alexander, Arden, Coletta, and Goldberg. Nonlinear rod-cone interactions involve a suppressive influence of rods on cone-mediated flicker sensations which is maximal when rods are totally dark-adapted. We now directly compare these two sets of mechanisms both by means of psychophysical procedures in humans and intracellular recording in subhuman species. These types of rod-cone interaction must be considered distinct since they have different magnitudes and different space and time constants. But since both types are observed in the same neurons in the distal most retina, they reflect the operation of the same elements simultaneously interacting with one another in several different manners.

© 1985 Optical Society of America