Exteroceptive control of response under delayed reinforcement

Three white rats, after 50 continuous reinforcements, were exposed successively, under dim illumination, to reinforcement delays of 1, 3, 5, 7.5, 10, 15, and 20 sec, with prolonged training at the 20-sec level. Behavior was maintained at each level, and an increase in interval was accompanied by an increase in post-reinforcement pause. Subsequently, under both 20- and 30-sec delays, the animals were tested during half of each daily session to determine the effect of introducing darkness during each delay interval. The result of this stimulus “support” was to regularize and increase response rate for each animal at both interval values