First, a series of simple descriptive equations are presented which suffice to describe the effects of variation of reward in differential conditioning. Central to these equations is the assumption that contrasted reward inhibits performance. Second, a variety of behavioral phenomena observed in the double-alley apparatus are interpreted as reflecting discrimination behavior and, therefore, the operation of an inhibitory effect of contrasted reinforcement.

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The results of two differential instrumental conditioning experiments showed that nondifferentially-re.inforced control groups ran faster in the 5+ alley ,in which discrimination 5s within the same squads received the more favorable inc entive, than in the 5-alley. This differential responding was tentatively attributed to odors exuded by discrimination 5s.

A total of 72 preshift and 144 postshift trials in the double alley runway was given to 48 female hooded rats randomly assigned to the following 3 groups: Groups 100-50, 100-0, and 0-0, designated according to preshift and postshift percentage reinforcement in the 1st goal box (Gi). Following the introduction of nonreinforcement, 2nd alley starting speeds for both Group 100-0 and Group 100-50 on Gi nonreinforced trials were enhanced. The facilitative effects of nonreinforcement dissipated for Group 100-0, but persisted for Group 100-50. Group 100-50 1st alley starting speeds increased while Group 100-0 speeds decreased following the introduction of nonreinforcement. The results were interpreted as supportive of the frustration theory assumption that the parameters of frustration are dependent upon the strength of reward expectancy in the 1st alley.1 This experiment represents a portion of a dissertation submitted to the Psychology Department of the State University of Iowa in partial fulfillment of the requirements for the PhD degree. The author wishes to acknowledge his indebtedness to Kenneth W. Spence for advice and assistance throughout the course of the investigation. The experiment was conducted during the author's tenure as a National Science Foundation Cooperative Graduate Fellow.

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