Effects of LSD on a visual discrimination between real and illusory stimuli by macaca mulatta

Includes bibliographical references (pages 47-50)Rhesus monkey--Behavior.Four rhesus monkeys were trained on a simultaneous visual discrimination between a real ???M&M??? candy and a 3-D projection of a ???M&M??? (illusory stimuli). Two animals were reinforced for responses made only to the real, red M&M (color relevant group) and the other two animals were reinforced for responses made only to the real M&M, irrespective of color (reality relevant group). Following acquisition of the task, probe trials (trials in which color was irrelevant) were randomly presented among the regular sessions to ascertain which cue, color or reality, the animals were responding to. Initial probe tests revealed that monkeys trained with color relevant and reality irrelevant\ud were impaired in accuracy when color was removed whereas monkeys trained with reality relevant were unimpaired by changes in color. After several days of probe tests, however, both groups were able to discriminate on the basis of reality. Therefore further drug analyses treated all animals as one group.\ud Two hallucinogens, lysergic acid diethylamide (LSD), and dimethyltryptamine (DMT), both known to cause hallucinogenic effects, i.e., perceptual changes, were then administered in an attempt to disrupt previous accurate discriminations between the real and illusory stimuli. Other drugs, chlorpromazine (CPZ) and caffeine (CAF), which do not normally produce hallucinations in man, were also administered. The accuracy of performance for both groups was impaired (discrimination ratios < 50% and latency > 30 seconds) following the administration of the highest dose (128 meg/kg)* of LSD. A dose of 2 mg/kg of DMT, comparable to doses of 16 and 32 meg/kg of LSD, also disrupted performance on both measures, although not so dramatically. CPZ and CAF disrupted performance latency but not accuracy. These results suggest that hallucinogens produce changes in reality perceptions, i.e., perceptions between real and illusory stimuli