Simultaneous contrast as a function of test-field area.

Abstract

The brightness of a test-field rectangle was studied as a function of its area and the luminance of a nearby inducing-field rectangle. The area of the test field was varied by increasing its vertical dimension from 5.5'' to 33.0'' in visual angle. A binocular matching technique was used in which S indicated the test-field brightness by the luminance of a match-field set equal in brightness to the test field. Two experiments were performed. In the first the match area was held at a constant maximum value. In the second the match area was allowed to vary along with the test area. The dependent variable for both experiments was match-field luminance and the independent variables, test area, test luminance, and inducing luminance. Very little if any change occurred in the test-field brightness as a function of test-area variation in either experiments. This held true for a wide range of test and inducing luminances. As inducing luminance was increased, however, test brightness became depressed. A mathematical theory fit to the data was based upon physiological inhibitive interaction among individual cone receptors in the retina.