Efeito de Contraste na Preferência de Macacos-Prego (Sapajus apella) por Reforçadores

Abstract

The effectiveness of different food items as reinforcers on the control of behavior might vary with the context in which these reinforcers are produced. In capuchin monkeys (Sapajus apella), three potential determinants of such a context-dependent reinforcer valuation are: The presence of other reinforcers on the experimental setting, the prior history with more valued reinforcers and observing conspecifics producing higher-valued reinforcers. Brosnan and de Waal (2003) assessed how capuchin monkeys‟ performance on a token exchange task varied depending on whether a conspecific received the same or a better food as reinforcer for performing the same task. The results revealed that the target subjects rejected the food when the conspecific received the better food for the same task. The effect was later called the „inequity aversion‟ effect because it was alleged that monkeys opposed to reinforcement inequity. Procedural variations among studies, however, impose ambiguity and caution on interpreting the effect. Factors other than the inequity between subjects, such as the presence of the more-valued reinforcer in the experimental setting and “frustration” might well account for the rejections. Frustration can be defined as an instance of behavioral contrast in which changes in the reinforcement associated with one condition impact the behavior controlled by another reinforcement under a different condition. The present study aimed at properly isolating contrast effects in a token exchange task. Nine monkeys (Sapajus apella) were exposed to three conditions. In the first one, token exchange produced a less preferred food – cucumbers. The second one produced a preferred food – grapes. In the third condition, token exchange produced cucumbers again. It was expected that experience with the preferred food would lead to less acceptance or more rejections of the less preferred one on the third condition as compared to the first condition. The global results suggest a successive and transient negative contrast effect, and are unprecedented in this animal species. The generality of the results and the scope of conclusions impose caution though for there was considerable variability between subjects. Future studies should try and replicate the effect with more subjects and ensure performance stability in each condition before introducing the ensuing conditions.