Incentive contrast: A review of behavioral changes following shifts in reward

Abstract

The literature relevant to incentive contrast effects is reviewed, with emphasis on the data published since the reviews by Black (1968) and Dunham (1968). Contrary to the evidence available for the earlier reviews, the current literature indicates that positive contrast is a reliable phenomenon. Its occurrence is facilitated by use of a constant delay of reward, use of a long runway, or possibly by a shift while a negative contrast effect, resulting from a previous shift, is still present in the animals' behavior. Positive contrast also occurs in consummatory behavior when sucrose or saccharin solutions are shifted. Conditions that are ineffective in producing positive contrast are reviewed, as are the effects of numerous variables on both successive and simultaneous contrast. In addition, positive and negative contrast effects resulting from shifts in delay or percentage of reward, contrast resulting from shifts in sucrose, saccharin, or ethanol solutions, contrast in choice behavior, and transsituational contrast are reviewed. The relationship of the data to several theoretical interpretations of contrast is also considered.Interpretation of the behavior changes that occur when a familiar reward is replaced by a novel, usually less preferred, reward has played an important role in the theoretical analysis of animal learning. For example, Tolman (1932) cited the behavior of a monkey when the familiar reward of a banana was replaced by a piece of lettuce as evidence favoring his view that animals learn expectancies of particular rewards in a learning situation. The behavioral description was obtained in a delayed-response experiment by Tinklepaugh (1928): "She [the monkey] extends her hand to seize the food. But her hand drops to the floor without touching it. She looks at the lettuce but (unless very hungry) does not touch it. She looks under and around her. She picks the cup up and examines it thoroughly inside and out. She has on occasion turned toward observers present in the room and shrieked at them in apparent anger. After several seconds spent searching, she gives a glance toward the other cup, which she has been taught not to look into, and then walks off to a nearby window. The lettuce is left untouched on the floor" (p. 224).In addition to supporting Tolman's expectancy interpretation of animal learning, this description contains elements that continue to be relevant as possible explanations of the behavioral changes that Appreciation is due Alexandra Avdzej for assistance in library research and to HowardBecker, SusanChecke, and MaryFlaherty for their comments on the manuscript. Preparation for this article was aided by grants from the Rutgers Research Council. The author's mailing addressis: Psychology Department, Busch Campus, Rutgers University, New Brunswick, New Jersey08903. occur subsequent to reward shifts, that is, the apparent presence of an emotional response elicited by the shift and the possibility that the animals search for the missing reward, given the opportunity.A rat study by Elli...

Excitation and inhibition in unblocking.

“…Last, it is worth noting that unblocking experiments bear at least a superficial similarity to instrumental incentive contrast experiments (see Flaherty, 1982, for a recent review). Subjects are trained with either large or small rewards in the first phase, and then the rewards are either shifted to the other reward value or maintained in the second phase.…”

Animals prefer reinforcement that follows greater effort: Justification of effort or within-trial contrast?

“…Procedurally, the positive contrast effect reported by Clement et al (2000) appears to be most similar to that involved in anticipatory contrast (Flaherty, 1982) because in each case there is a series of paired events, the second of which is better than the first. High effort is followed by discriminative stimuli in the case of the Clement et al procedure, and a low concentration of saccharin is followed by a higher concentration of sucrose in the case of anticipatory contrast.…”

“…Furthermore, the behavior assessed is typically consummatory behavior rather than running speed. For example, rats often drink less of a weak saccharin solution if they have learned that it will be followed by a strong sucrose solution, relative to a control group for which saccharin is followed by more saccharin (Flaherty, 1982). This form of contrast differs from others in the sense that the measure of contrast involves differential rates of the consumption of a reward (rather than an independent behavior such as running speed).…”

“…This analysis suggests that the mechanism responsible for anticipatory contrast (Flaherty, 1982) and, in the case of behavioral contrast, responding in anticipation of a worsening schedule (Williams, 1981), is likely to be a compensatory or learned response. In this sense, these two forms of contrast are probably quite different from the perceptual-like detection process involved in incentive contrast.…”

Response to Ahrendt, Houlihan, and Buchanan

“…To begin with, the findings seem relevant to the literature on incentive contrast-behavioral changes due to shifts in reinforcer value. Dozens of studies with a range of species have shown that downward shifts in reinforcer value induce predictable changes in behavior, including aggression and other behavior incidental to the reinforcement contingencies (Flaherty, 1982;Pellegrini et al, 2008). What is notable about these findings is that a reinforcer capable of sustaining behavior in its own right loses its value when contrasted with a higher-valued reinforcer.…”