Abstract

Stimuli that are spatially and/or temporally periodic, but too high in frequency to be subjectively resolvable, appear by definition uniform and steady. If processing is linear up to the stage at which resolution losses obliterate the stimulus modulation, this stimulus will match a uniform and steady stimulus of the same average luminance. The phenomena of difference-frequency gratings and contrast-modulation flicker are exceptions to this principle for unresolvable gratings in cone vision, and the direction of deviation from linearity suggests that a compressive or sensitivity-regulating nonlinearity precedes any neural spatial integration in the cone system. This nonlinearity is a dynamic one rather than an instantaneous compression. In the rod system, on the other hand, the spatially integrated signals are very nearly linear, even at saturating levels. In the short-wavelength cone system, compressive nonlinearity precedes both spatial and temporal integration, the latter being revealed in deviations from the Talbot-Plateau law under some conditions.

© 1992 Optical Society of America