Observational learning in monkeys.

Observer monkeys were housed next to demonstrator monkeys that were conditioned to respond on a multiple reinforcement schedule whose components were fixed-ratio 32, variable-interval 3-min, and extinction 5-min followed by an additional 30 sec of extinction during which every response started a new 30-sec interval. After observational periods from 113 to 210 hr long, during which observers could not perform the response and were given no extrinsic reinforcers, their first-response latencies to fixed ratio and variable interval were as short as the demonstrators; and their rates of responding were well above pre-observational baseline levels. About 8 hr later, a temporal pattern of responding appropriate to the multiple schedule emerged, including non-emission of responses during extinction. Controls lacking the chance to observe did not develop typically patterned responding after 60 hr in one case and, in two other cases, after 80 hr during which, on two occasions, every one of 50 responses was reinforced. In a second experiment, the stimulus lights associated with fixed ratio and variable interval were presented simultaneously. Subjects chose one of the schedules by responding to one of the levers beneath the lights. All subjects initially chose fixed ratio. Seeing the demonstrators switch to variable interval, due to increases in the fixed-ratio requirement, had no effect upon observers, which continued to choose fixed ratio.