Abstract
Two monkeys were trained to press and hold down a telegraph key in the presence of a red light. Subsequent release of the key in response to a white cross superimposed on the red background was followed by reinforcement. Key release in response to a white circle on the red background was never reinforced. Latencies for the key release response to the reinforced stimulus (cross) were considerably shorter and less variable than those to the unreinforced stimulus (circle).