Motivating operations affect stimulus control: a largely overlooked phenomenon in discrimination learning.

Several recent studies have explored what Michael (e.g., 1982) termed the value-altering effect and the behavior-altering effect of motivating operations. One aspect of the behavior-altering effect that has garnered no recent attention involves changes in stimulus control produced by motivating operations. To call attention to this aspect of the behavior-altering effect, we herein review 11 studies that are concerned with the influence of varying levels of food or water deprivation on stimulus generalization. These studies suggest that motivating operations influence stimulus control (a) by changing the evocative strength of not just an established discriminative stimulus, but also of stimuli that are physically similar to it; (b) by changing the range of stimuli that evoke the operant in question; and (c) by exerting these effects in a graded fashion. These findings are potentially of conceptual and applied significance, and it appears that further research examining how motivating operations alter stimulus control, including some studies suggested herein, is warranted.