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...

In four experiments, the once daily availability of saccharin (.15%) preceded the availability of sucrose (32% or 2%). Experiment 1 showed that the intake of saccharin was reduced when it preceded 32% sucrose but not when it preceded 2% sucrose, as compared with saccharin-alone conditions. Experiment 2 showed that less saccharin was consumed when the saccharin preceded sucrose by 5 min than when there was a 30-min intersolution interval. Experiment 3 replicated this finding and showed that the presentation of the two solutions through the same or different access holes in the apparatus was not relevant to the result. Experiment 4 showed that there was an inverse relationship between saccharin intake and the length of the intersolution interval in the range of 1 to 30 min. These data were interpreted to indicate that the animals learn the predictive relationship between the saccharin and sucrose solutions and that the intake of the saccharin is reduced by an anticipatory contrast mechanism-a mechanism that may have restricted temporal parameters.The juxtaposition of sucrose solutions of high and low concentration leads to a reduced intake of the solution of lower concentration compared with conditions in which only the lower concentration is experienced. This diminished intake occurs when the lower concentration is presented after the animal has had extended or minimal experience with the higher concentration (Flaherty, Ciszewski, & Kaplan, 1979; Flaherty, Troncoso, & Deschu, 1980;Vogel, Mikulka, & Spear, 1968), as well as when the two solutions are repeatedly alternated in availability (Flaherty & Largen, 1975;Flaherty & Sepanak, 1978).The diminished intake is termed a negative contrast effect-successive negative contrast when the lower concentration is presented after some experience with the higher concentration, and simultaneous negative contrast when the two solutions are repeatedly juxtaposed. There is some evidence that these two types of contrast may be controlled by somewhat different mechanisms (e.g., Flaherty, Lombardi, Wrightson, & Deptula, 1980).Recently we have found indications of another type of contrast, anticipatory contrast (Flaherty & Checke, Note 1). In the course of a study investigating possible conditioning of the glucoregulatory system with saccharin as a CS and sucrose as aVeS, we saw some evidence that the intake of saccharin was reduced when it served as a predictor of sucrose. The studies described in this paper explored this phenomenon. EXPERIMENT 1The purpose of the first experiment was to determine whether the presentation of a sucrose solution 5 min after the daily availability of a .J5070 saccharin solution would lower the intake of saccharin. A second purpose was to determine whether the concentration of the sucrose solution was important in determining the degree of suppression of saccharin.The basic procedure in this experiment, as well as in most of the other experiments in this paper, was as follows. A tube containing a .15% saccharin solution was made available for a 3-mi...

Contrast in consummatory behavior occurs readily when a less preferred substance follows a preferred substance. A previous experiment indicated that contrast in consummatory behavior may also develop when a less preferred substance precedes a preferred substance in brief daily exposures. In the present experiment, the same animals sometimes received 0.15% saccharin followed, 15 sec later, by 32% sucrose (.15-32) and sometimes received 0.15% saccharin followed by the same 0.15% saccharin solution (.15-.15). One solution pair was given each day, and the two conditions, .15-32 and .15-.15, occurred in alternation across days. The two different solution conditions were correlated with different cues. Saccharin intake from the first tube was lower when the second tube contained 32% sucrose than when it contained .15% saccharin, both in original discrimination training and following a reversal of the cue-solution pairings. These results support the conclusion that contrast in this situation is based on the anticipation of the impending 32 % sucrose each day, rather than on a retrograde comparison with the 32 % sucrose received the previous day. These data are considered in terms of Pavlovian conditioning outcomes when the CS is a stimulus with hedonic value.

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Rats suppress intake of an acceptable substance (e.g., 0.15% saccharin) when it is followed by a preferred substance (e.g., 32% sucrose) in once per day pairings. The role of a learned devaluation of the initial solution in suppressed intake (anticipatory negative contrast) was investigated. The findings included the following: (a) Flavors or odors as within-subject cues precluded the occurrence of anticipatory contrast, conditioning flavor and odor preferences instead, which appeared to antagonize suppressed intake. (b) Anticipatory contrast was obtained when within-subject context cues, temporal alternation cues, or drinking-spout cues were used. (c) Preference tests conducted with the spout cues showed that devaluation of the initial substance was not necessary for the occurrence of negative anticipatory contrast.