Individual differences in pulse brightness perception

When brightness-pulse duration relations are studied with a simultaneous brightness discrimination procedure, three classes of observers emerge (Bowen & Markell, 1980). These classes are defined by whether or not observers perceive temporal brightness enhancement (the Broca-Sulzer effect) under two asynchrony conditions for pulses to be compared: simultaneous onset and simultaneous offset. Type A observers perceive brightness enhancement for both asynchrony conditions; Type B observers perceive brightness enhancement for simultaneous offset of pulses but not for simultaneous onset; Type C observers do not generate the Broca-Sulzer effect under either asynchrony condition. Here we present supplementary measures on observers of all three types: (1) magnitude estimation of the brightness of single pulses of light of varying duration, (2) modulation sensitivity for sin~wave flicker, and (3) contrast sensitivity for moving sine-wave gratings. The magnitude estimation data differentiated the three types of observers, but flicker and motion sensitivity did not. The three classes of observers probably differ in the perceptual criteria they employ in judging the brightness of isolated pulses of light; they probably do not differ in their underlying neurophysiological responses.