REINFORCEMENT DURATION AND THE PEAK SHIFT IN POST‐DISCRIMINATION GRADIENTS 1

Abstract

Pigeons were trained to key‐peck for food, first with single‐stimulus training and then with successive discrimination (multiple schedule) training. In the multiple schedule, two different wavelengths were each correlated with equally frequent variable‐interval reinforcement but different durations (6 sec vs. 2 sec) of access to grain. For some birds, the different durations of feeding cycle were cued by different intensities of the food hopper light. For some of these “cued” birds, single‐stimulus training had been carried out with 6‐sec feedings and when multiple‐schedule training was introduced, the novel stimulus was correlated with 2‐sec feedings. For the others, 2‐sec feedings were originally used, and the novel stimulus was then present during the 6‐sec reinforcement duration. The cueing procedure enhanced discrimination performance, and was necessary for the consistent production of a peak shift. In addition, the condition in which original training had been carried out with 6‐sec feedings, and thus reinforcement duration was reduced in the presence of the novel stimulus, led to the best performance.