Positive and negative contrast effects as a function of shifts in percentage of reward

Abstract

Two experiments examined the effects of shifts in reward percentage on acquisition of an instrumental running response. In Experiment 1, a group shifted from 33% reward to 100% reward ran faster following the shift than did a group that received 100% reward throughout training; that is, a positive contrast effect was observed. In Experiment 2, animals shifted from 100% to 33% reward exhibited a negative contrast effect; that is, they ran slower following the shift than did control animals that received 33% reward in both phases of the experiment. The results were discussed in terms of Capaldi's reinforcement-level theory.Capaldi (1978) It is clear that, in addition to explaining the effects of reward percentage on Rn, the reinforcement-level model can be extended to make predictions concerning acquisition effects of reward percentage. The experiments reported here examined two such predictions. EXPERIMENT 1According to the reinforcement-level model, positive contrast (i.e., faster running in a group shifted from small to large reward than in a group that always receives the large magnitude) occurs whenever an animal receives a larger reward than it expects. This discrepancy between expected and obtained reward for the upshifted animals results in a greater accumulation of habit, which elevates responding above that of nonshifted control

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

“…All five papers that included the proper controls found evidence of a SucNCE when schedules were made leaner (Dyck et al, 1977;Fox, 1972; McHose & Peters, 1975;Seybert, 1979). In the McCain et al study, the NCE occurred only on the third shift in a LSLS sequence of shifts.…”

“…For example, SucPCEs should be long lasting. This sometimes happens (e.g., Mellgren, 1971aMellgren, , 1973Seybert, 1979),but sometimes does not (e.g., McHose & Moore, 1978;Premack & Hillix, 1962;Seybert & Mellgren, 1971). McHose and Moore, whose paper was designed to compare the magnitude and the duration of both contrasts, found them similar in magnitude and SucPCEs to be of relatively short duration.…”

“…Leung and Jensen (1968) found evidence of SucPCEs when rats were shifted from 33070 or 17% schedules to 100% reinforcement. SucPC was also obtained by Lehr (1974) in two experiments and by Shanab and Cavallaro (1975) in one experiment, all involving 50% to 100% shifts, by Seybert (1979) in a 33% to 100% shift, and by Fox (1972) and Dyck, Dresel, Thiessen, and DiLollo (1977) in 25% to 50% shifts. Only two studies failed to find SucPCEs: one by Roop and Nation (1976) in a 50% to 100% shift and one by McCain, Lobb, and Newberry (1976) in a 25% to 75% shift.…”

The reversed work-ethic effect: Monkeys avoid stimuli associated with high-effort1

“…For example, subjects that are shifted from a larger to a smaller reward in a runway run slower following the shift than subjects that always receive a smaller reward (Flaherty, 1982). Although most of these studies shifted the amount of reward to produce the contrast effect, some studies (Fox, 1972;Seybert, 1979) showed the contrast effect by shifting the amount of effort to obtain a reward, as in studies on the work-ethic effect discussed here.The deteriorated performance is attributed to frustration that is produced by a less attractive reward compared to an anticipated reward or by demanding more effort to obtain a reward (Amsel, 1958; see also Amsel, 1992;Bower, 1961). Previous studies have shown that the negative contrast effect was widely evidenced in rats (Crespi, 1942;Seybert, 1979;Vogel, Mikulka, & Spear, 1968) and even human infants (Kobre & Lipsitt, 1972); however, extensive studies have failed to obtain the negative contrast effect in pigeons (Papini, 1997).…”

“…The deteriorated performance is attributed to frustration that is produced by a less attractive reward compared to an anticipated reward or by demanding more effort to obtain a reward (Amsel, 1958; see also Amsel, 1992; Bower, 1961). Previous studies have shown that the negative contrast effect was widely evidenced in rats (Crespi, 1942; Seybert, 1979; Vogel, Mikulka, & Spear, 1968) and even human infants (Kobre & Lipsitt, 1972); however, extensive studies have failed to obtain the negative contrast effect in pigeons (Papini, 1997). From this viewpoint, monkeys in the present experiment would experience frustration with the FR20‐schedule (high‐effort) when they had obtained a reward by low‐effort (i.e.…”