Response strength as a function of drive level and pre- and postshift incentive magnitude.

Abstract

To ascertain (a) the function describing how D and K combine and (b) the effect of incentive magnitude shifts as a function of D, speed measures were obtained on four groups of rats involving two drive levels and two reward levels. After 90 trials on the original reward level, the reward of each group was shifted to that of the other for 25 additional trials. Statistical analyses revealed a significant interaction (P = .05) between D and K, indicative, not of a multiplicative function but of a negatively accelerated one such as exponential addition. Both main effects were highly significant but t tests were significant only between the two low- drive groups and between the two low-reward groups. After the shift in incentive magnitude, changes in running speed occurred in the expected direction but the differences were much greater under high drive than under low drive. It was hypothesized that such differences (i.e., Crespi effect) were an increasing function of D and the extent of the shift in incentive magnitude. The shift data were interpreted in terms of the hypothetical anticipatory emotional response mechanism (re[forward arrow] Se).