Brown induction is both quick and proximity dependent

Abstract

Bright surround stimuli will change the hue of a target from yellow to brown. To help characterize the mechanisms of brown induction, we ask how fast this occurs and whether the latency depends on the proximity of surround stimuli to the target. Five observers viewed a 2° diameter foveal target disk surrounded by a large, bright (124 cd/m² CIE 1964) annular surround with a gap of 0°, 0.25° or 1° between target and surround. Both surround and target stimuli were presented for either 1 s or 30 ms, with only small fixation dots visible for 3 s between stimulus presentations. Observers adjusted the luminance of the target to the highest light level at which the target appeared pure brown, with no trace of yellow: the higher this “brown boundary”, the more effective the surround is at inducing brown. This boundary varied from 1 to 13 cd/m² under the present conditions. We found that brown induction (a) occurs rapidly (within 30 ms) and strengthens slightly with longer-duration (1 s) stimuli, and (b) becomes stronger with closer proximity of target and surround regardless of stimulus duration. Thus, brown induction is found for brief stimuli and maintains both strength and proximity dependence with longer test duration. In this regard, brown induction differs from brightness contrast, which loses both strength and proximity dependence with increased stimulus duration, and from color contrast, which loses strength but not proximity dependence with increased stimulus duration (Kaneko & Murikama, 2013).