Models of retinal signal processing at high luminances

SummaryIn psychophysics the relation between the threshold luminance increment and the background luminance for visual increment detection, is known to become linear for high luminances. This so called Weber-law means that at high luminances the threshold is caused by the detection apparatus, and not by the quantum noise of the stimulus itself. A simple machine implementing the Weber-law is discussed. This machine obviates the need for an internal noise source (or dark light). It is the combined result of an apparatus that reduces the output event rate by causing the quantum to spike ratio to follow the input intensity, and a detection criterion that needs a constant number of extra output events to generate a positive response. The dynamic properties of the machine are described by the solutions of a simple though nonlinear differential equation. The supra threshold properties prove to mimic several of the responses known to occur at ganglion cell level in the cat's retina. A tentative model of an on-center receptive field is presented, and results obtained by simulating this model on a digital cumputer are compared with some recent electrophysiological findings. Finally a possible extension of the model to a full on-center/off-surround receptive field model is discussed.