In many situations, a patch of light appears several times brighter when briefly flashed than when viewed for longer durations. This aspect of visual perception is known as temporal brightness enhancement, or the Broca-Sulzer effect. Brightness enhancement has been measured by several psychophysical methods. The magnitude of the effect is known to be influenced by such physical properties of the test target as luminance, area, and chromaticity. The proposed study intends to measure the magnitude of the brightness enhancement effect using a target of constant physical properties in conjunction with various surround stimuli appearing outside the target area. A previous experiment (Corwin and Giambalvo, 1974) demonstrated that a steady surround can greatly reduce the magnitude of brightness enhancement. The proposed study intends (1) to determine whether a sufficiently intense surround can totally obliterate brightness enhancement, and (2) to establish the extent to which the reduction in brightness enhancement is due to lateral inhibitory influences or to adaptation produced by stray light. This will be done by measuring brightness-versus-duration curves for a test target viewed in conjunction with surround fields varying in luminance, spatial configuration, and time of appearance with respect to the test target. The results of the proposed experiments may help to decide among alternative explanations of the brightness enhancement effect.