TEMPORAL LIMITS OF BRIGHTNESS INDUCTION AND MECHANISMS OF BRIGHTNESS PERCEPTION

The luminance of a squarewave grating was modulated in a manner such t hat every other stripe temporally varied between bright and dark and t he intervening stripes had constant luminance. This produces brightnes s induction in the constant stripes, roughly in antiphase to the lumin ance modulation. We used this stimulus as a probe to explore the tempo ral properties of brightness induction and the mechanisms determining perceived brightness. Over a range of spatial frequencies we measured: (1) the highest temporal frequency at which brightness induction occu rs; (2) the magnitude of induced brightness; and (3) the temporal phas e of the induced brightness modulation. We find that brightness induct ion ceases with luminance modulation above a cutoff temporal frequency that depends on spatial frequency. The magnitude of induced brightnes s modulation is greatest at low spatial frequencies and low temporal f requencies. Induced brightness lags behind the luminance modulation an d this phase lag increases as spatial frequency decreases. All of thes e findings can be understood as consequences of an induction process t hat takes longer to complete as the induction region increases in size . Copyright (C) 1996 Elsevier Science Ltd.