Abstract

As part of our attempt to construct a computable model of the dynamics of light adaptation, we consider a class of models that contain four stages: (1) early noise, (2) a deterministic filtering and gain-changing stage, (3) late noise, and (4) a decision rule that is either an ideal (signal-known-exactly) detector or a peaktrough detector. With the ideal-detector and without late noise, the observer's sensitivity as a function of mean luminance and temporal frequency is not affected by the filtering and gain-changing stage. Consequently, if the early noise consists entirely of quantal fluctuations, sensitivity will always be a square-root function of mean luminance and a uniform (flat) function of temporal frequency. This latter prediction is contradicted by all known data; either the ideal-detector is the wrong decision rule, or sensitivity is almost always limited by sources of noise other than quantal fluctuations. With the peaktrough detector, however, with or without late noise, the observer's sensitivity as a function of temporal frequency does reflect the sensitivity of the low-level filtering and gain-changing stage. Late noise is needed, however, if the observer's sensitivity as a function of mean luminance is to go through both a square-root region and a Weber region.

© 1990 Optical Society of America