Visual Responses to Time-Dependent Stimuli* II Single-Channel Model of the Photopic Visual System

A relatively simple model of the first two links in the visual receptor system is proposed in order to explain the data reported in Part I on amplitude sensitivity to sinusoidally flickering stimuli at photopic adaptation levels of white light [ J. Opt. Soc. Am.51, 422 ( 1960)]. The model consists of a linear filtering stage followed by a nonlinear pulse-encoding stage. The first stage is regarded as essentially “noiseless” at photopic levels; amplitude thresholds are treated as thresholds for the transmission of variable intervals between pulses. With the aid of the model, suprathreshold responses can be inferred from the measured threshold behavior. In this way, transient responses comparable with various other psychophysical, neural, and electroretinographic data are predicted; the resulting agreement is considered fairly good in view of the parsimony of the proposed model.