Multiple shifts in reward amount were given to rats in a straight runway. Both positive and negative contrast effects were observed. A positive contrast effect was observed, however, only if the shift from small to large reward occurred while the subject was evidencing a negative contrast effect. Implications for current conceptions of reinforcement contrast are discussed.

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After receiving large rewards in a straight gray runway during Phase I, rats were given small rewards during placement trials (Phase 2) in a gray housing cage or in a gray goalbox. During Phase 3, only animals receiving small reward in housing cage placement trials showed a successive negative contrast effect (NCE). The results suggest that alley cues other than brightness mediate the NCE and are supportive of frustration theory.Animal research in instrumental conditioning is replete with data showing the effects of a shift in reward magnitude (Black, 1968) in the runway . Specifically, many studies have shown that rats shifted from large to small magnitude of reward run more slowly than rats maintained on small magnitude of reward, a phenomenon designated as the negative contrast effect (NCE) (e.g., Capaldi & Lynch, 1967;Crespi, 1942;Ehrenfreund, 1971; Gonzales, Gleitman, & Bitterman, 1962). Studies by Calef and his associates (Calef, 1972;Calef, Calef, Prochaska, & Geller, 1978; Calef, Hopkins, McHewitt, & Maxwell, 1973;Maxwell, Calef, Murray, Shepard, & Norville, 1976) have shown the frustration theory account of the NCE (Amsel, 1958(Amsel, , 1962 to be the most reliable. Frustration theory suggests that alley cues are particularly important in producing the NCE. According to Amsel (1958Amsel ( , 1962, alley cues such as brightness should elicit the "expectancy" (rg-sg) for large reward during the initial postshift period. After receiving less than "expected," the subjects should experience frustration and produce depressed speeds.Recently, Capaldi (1978) presented results that appear to conflict with a frustration interpretation of the NCE ("depression" effect). In the Capaldi study, animals that received a simultaneous shift in reward and alley brightness (large black to small white) produced approximately as much of a NCE as animals that received only a shift in reward (large white to small white). These results imply that alley cues (brightness) were not instrumental in mediating a NCE. In other words, if alley cues were praying a major role in mediating the "depression" effect, changing the brightness from one phase to another should have resulted in less rg-sg to large reward being elicited by the alley, which in turn Reprint requests should be sent to Richard S. Calef, West Virginia Wesleyan College, Buckhannon, West Virginia 26201.should have produced less frustration and depressed speeds.However, Capaldi's (1978) findings may be supportive of a frustration account of the "depression" effect in that brightness may not be the main alley cue playing a significant role in mediating a NCE. Other cues such as texture, size, shape, or the cover of the apparatus may have been the relevant cues associated with large reward expectancy, since these cues did not change from preshift to postshift periods. To eliminate the latter cues would necessitate presenting the postshift phase in an apparatus other than the runway. This, of course, would make the findings less applicable to previous NCE research produced in...

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