Discrimination of luminance increments and decrements

Discrimination of pulsed increments from decrements improves relative to detection when the adaptation level is decreased or stimulus duration is increased. Using Tanner's theory of recognition [J. Acoust. Soc. Am. 28, 882 (1956)], we show that the subject's internal decision variables corresponding to the increment and decrement stimuli also show increased statistical independence as adaptation is decreased or stimulus duration increases. We infer from this result that at high adaptation levels detection is based predominantly on information in one channel, whereas at low adaptation levels there is information from two channels. Similarly, for long durations, we infer two independent channels, which contribute little information about the sign of the stimulus at short durations.