Brightness contrast from adjacent and nonadjacent lights

Abstract

The brightness of a small patch of light depends on the luminance of the light itself and other lights nearby. We examine the neural level within the visual system at which a remote noncontiguous light in the visual field affects the brightness of a test patch. Consider a 20′ test, a 3° surround, and a 3-5.4° outer ring adjacent to the surround. Initially we quantified the change of brightness caused by the remote outer ring by directly matching a comparison standard to the brightness of the test-with-surround, first with and then without the outer ring. As expected, the outer ring affected the brightness matches. In the next experiment, the test and comparison standard were presented haploscopically: in each eye, an outer ring enclosed a circular field surrounding a small patch, as before. The patch in the left eye was the comparison patch and was presented to the left of center (although still well within the circular surround); the patch in the right eye was the test patch, presented to the right of center. The fused percept was a single outer ring, a single surround, and two small separated patches. The outer ring had little or no effect on the haploscopic brightness matches. The results can be accounted for by adjacent surrounds affecting neural signals at the retinal level and more remote lights affecting signals after binocular combination. A necessary condition of the outer rings disturbing a brightness match may be that the two surrounds are seen as different in brightness.