The effects of drugs on the discrimination of color following a variable delay period: a signal detection analysis.

Six pigeons were trained in a chamber with three response keys. Following an observing response on the center key, either colored or noncolored (white) lights were projected on that key. A second center key observing response provided an opportunity to respond on one of the side keys, appropriate to the stimuli presented, to obtain food; responding on the incorrect side produced a 30-s time-out. A delay period of varying duration with no stimuli followed stimulus presentation; the length of the delay was determined 'on-line', such that performance would be maintained at about 80% correct. Lysergic acid diethylamide (LSD, 0.04-0.2 mg/kg) had no significant effect on the accuracy of the discrimination (overall percent correct responses), even at doses that produced cessation of responding in some animals. Amphetamine (1-4 mg/kg) and morphine (0.5-4 mg/kg) decreased accuracy by decreasing sensitivity (A') and had little effect on reaction time. Haloperidol (0.5-2 mg/kg) had no significant effect on any measure of performance. None of the drugs altered response bias (B").