Body Weight, Short-Term Satiation and the Response to Reward Magnitude Shifts

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Abstract
It was confirmed that highly reliable “over-shooting“ (O-SH) and “undershooting” (U-SH) can be obtained when a stimulus associated with a contrasting magnitude of reward intrudes briefly into a session in which the animal receives either a high or low magnitude of reward as a baseline condition (Baltzer and Weiskrantz, 1970). These effects may be related to Crespi “elation” and “depression” effects, but it is also possible that they are dependent on differences in the amount of food ingested on the two baseline conditions. The effects of variations in body weight and pre-feeding in the rat were examined. The optimal level for obtaining the effects lies around the 95% body weight level. With body weight held constant, alterations in short-term satiation induced by pre-feeding before all sessions did not significantly change the magnitude of intrusion effects except in one extreme instance that might be accounted for by a basement effect. Differences in satiation level between the two baseline conditions can affect powerfully the magnitude of O-SH and U-SH, but nevertheless when such differences are eliminated reliable effects are still found. Arguments are advanced as to how short-term satiation and long-term deprivation factors might account for the magnitude of O-SH and U-SH, and reasons offered for considering that O-SH and U-SH have an emotional basis.