Human reaction time to negative contrast stimuli.

Simple motor reaction time (RT) to 100 percent negative contrast stimuli was measured for various background luminances as well as after bleaching a fraction of retinal photopigments. RT decreased to asymptotical value with the increase of background intensity. The intensity-dependent portion of RT behaved identically for 100 percent positive and negative contrast. Moreover, RT to 100 percent negative contrast was extended by bleaching and falls down during the adaptation to the lower background luminance. The results were discussed on the basis of the Pulfrich latency researches.