Acquisition of lever pressing in rats under a intermittent schedule of delayed reinforcement

Abstract

Lever-pressing by nine naive rats was acquired using delayed reinforcement delivered by a tandem Random Interval 30 s, Fixed Time t s schedule. For three rats each the value of t was 6, 12 or 24 s. Once responding was acquired, delay duration was progressively shortened to one-half of its preceding value, using the same subjects. During acquisition response rates were higher under shorter delays, i.e., in the form of a delay gradient. However, shortening the delay using the same subjects produced different effects on rate, depending on the delay value used during acquisition. This last finding was interpreted as evidence of a history effect.