Drugs and visual perception: effects of LSD, morphine and chloropromazine on accuracy, bias and speed.

Ten pigeons were trained to discriminate between the intensities of two white lights (projected behind a center response "key") using a discrete trial procedure in which choice behavior involved pecking at red or green lights projected behind left or right side keys. LSD (0.02-0.08 mg/kg) did not alter the accuracy of the brightness discrimination (percent correct) although it did lower response speed and may have differentially affected spatial (position) bias. Morphine (2.5--10.0 mg/kg) decreased accuracy of discrimination as well as response speed and had greater effects on trials when the bright stimulus was presented than when the dim stimulus was presented. Chlorpromazine (7.5-3.0 mg/kg) lowered accuracy without significantly altering any other measure of performance.