Foveal information processing at photopic luminances.

Abstract

A tentative model of information processing in the human fovea at photopic luminances is described, that handles both luminosity and chromaticity signals. The model consists of a “scaling-ensemble”, a group of sealers with common scaling-factor that provide an effective compression of the dynamic range of the input signals. The scaling factor adapts in such a way that the model conforms to Weber's law for the detection of short, small flashes on a bright background. The dynamics of the adaptation is such that the model effectively computes the logarithmic time derivative of the input signal. The model predicts the outcome of several psychophysical experiments. The predictions include Weber's law, Bloch's law, the apparent brightness of suprathreshold flashes as a function of adaptation level, the influence of spatial inhomogeneities on the perception of flicker, and the transfer function for moving sinusoidal bar patterns for both luminosity and chromaticity modulations. The influence of involuntary eye-movements on the perception of spatial patterns is also discussed. Finally an attempt is made to locate the components of the model in the anatomical structure of the retina. A tentative scheme of neural connections in the human fovea is presented.