Flicker and suprathreshold spatial summation: Evidence for a two-channel model of achromatic brightness

Abstract

Spatial summation of brightness was measured in the light-adapted periphery for targets that either flickered at 20 Hz or remained steady during a 1-sec exposure. For each target condition, stimuli of different diameters were adjusted in intensity to match a constant foveal reference target in subjective brightness. For comparison, increment thresholds were also measured. Large differences were found among the resulting equal-brightness functions of three normal observers. The data are consistent with a two-channel model of achromatic brightness. The spatial and temporal properties of the two brightness channels resemble those of the tonic and phasic systems of electrophysiology. © 1984 Psychonomic Society, Inc.