Abstract

Scotopic backgrounds can raise increment thresholds for photopic test stimuli (CXR) and vice versa (RXC). CXR is ubiquitous with variation of test stimulus duration (20-1000 ms) and size (6-120 min of arc) but varies tremendously with retinal eccentricity. At 4°, only 0.2-0.4 log unit of CXR is found, and only on small backgrounds. At 10°, up to 1.4 log unit of CXR is found, with at least 0.2 log unit on any size background. These results parallel previous findings for RXC¹ except that the direction of eccentricity dependence is reversed. The results are consistent with the center-surround model of interaction and parallel with spatial sensitization.

© 1985 Optical Society of America