Contrast discrimination in the cat.

Cats were trained to discriminate between two sinusoidal grating patterns differing only in contrast. The smallest discriminable contrast difference was determined for a number of different baseline contrast levels, and the resulting contrast increment thresholds plotted in the form of a contrast discrimination function. The resulting function was linear when plotted on log/log coordinates and the slope of this function varied with spatial frequency. These behavioural results are compared to the contrast/response properties of retinal and cortical neurones.