Temporal properties of spatial contrast vision.

The temporal characteristics of spatial contrast vision at and above threshold were assessed psychophysically using sinusoidal gratings and a contrast-matching method. Temporal frequency response curves became flatter as contrast level increased. An impulse response model was fitted to these flicker data, and used to make predictions about temporal integration and two-pulse summation. The predictions fitted the experimental data well, except under conditions where the Broca-Sulzer effect occurred. The latter was not predicted by the biphasic impulse response that otherwise worked well. Temporal filtering became moderately transient and operated over a shorter time-scale as contrast increased, and above threshold temporal properties varied little with spatial frequency. The data and modelling supported the idea that subjects exploited probability summation at threshold while using a peak detection criterion above threshold. Systematic visual field asymmetries in contrast perception are also described. Single- and multiple-channel models of temporal processing are discussed.