Theory of flicker and transient responses. I. Uniform fields.

Photopic flicker data are explained in terms of a theoretical model of two retinal processes. The first is a linear diffusion process (presumably in the receptors), with a large dynamic range (∼105). The second is a nonlinear inhibiting network (neural feedback at the synapses of the plexiform layers) that adaptively controls the sensitivity and time constants of the model. The magnitude of its transfer function fits the flicker data quantitatively at all frequencies, over a wide range of adaptation levels. The corresponding small-signal impulse responses are also calculated: their latencies and leading edges (associated with receptor activity) are invariant with adaptation level; the remaining phases of these transient waveforms (associated with the graded potentials of secondary neurons) adapt strongly, in accord with current histology and micro-electrode findings.