Dynamics of choice and frequency of environment change

Recent research has examined the effects on behavioral adjustment of a range of within-session changes in the reinforcer ratio available from two alternatives. Regularities between extended patterns of behavior (choice) and a distribution of food deliveries (expressed as a food-rate ratio) have emerged from such studies. To assess the generality of these findings, the present study manipulated rats' experience in the choice situation. Sixteen rats were divided into two groups of eight rats each. Seven non-signaled food-rate ratios were arranged to occur for responses on two concurrently available levers. Group 1 experienced a different food-rate ratio every day; each ratio provided 70 food deliveries, and none of the seven ratios operated for 2 consecutive days. Group 2 experienced the same sequence of food-rate ratios, except that each food-rate ratio remained in effect for 17 consecutive days (providing 70 food deliveries per session), after which a different food-rate ratio was selected for the next 17 sessions. In all cases, preference was adjusted to changes in food-rate ratios. Estimates of sensitivity to changes in food-rate ratios increased with an increasing number of sessions (i.e., experience in the choice situation). © 2008 Elsevier B.V. All rights reserved