ANALYSIS OF REACTION TIMES TO COLOURED STIMULI

Abstract

Reaction times were measured for 10- and 500-ms coloured stimuli at three different threshold intensity levels. The stimulus intensity of a 1 degree foveal flash detected with a probability of 0.5 was taken as the threshold intensity level. All flashes were superimposed on a 1000-td white background. The reaction time distributions were classified in terms of sustained- and transient-like responses. The distributions for the 0.5-s blue, red and white flashes all appear sustained-like at the subthreshold and threshold intensity levels. As the blue, red and white flashes were probably detected by different systems (colour-opponent and luminance) it appears that the sustained-like response is not a prerogative of any particular detection system. The responses to the blue flashes are on average about 80 ms longer than those to the white and red flashes. This difference can be attributed to a somewhat slower operation of either the blue-sensitive cones or of the blue/yellow opponent system. The responses to the white 10-ms flashes are about 120 ms faster than those to the 500-ms flashes. This considerable difference may reflect the faster response of the transient system.