Lawrence Weinstein

Negative incentive contrast effects with saccharin vs sucrose and partial reinforcement

Thirty male hooded rats received seven sessions of barpress training with sucrose (16% or 4%) and saccharin (.10% or 1.5%) as reward, followed by a shift from 16% to 4% sucrose and.10% to 1.5% saccharin. Four dependent measures indicated that concentrations of sucrose and saccharin that produced equivalent levels of performance produced equivalent negative contrast effects. In Experiment 2, 18 male hooded rats received four sessions of barpress training with (.10% or 1.5%) saccharin under an FR 7 schedule of reinforcement followed by a shift from.10% to 1.5%. Four of the five measures indicated negative contrast effects. Confounding inherent in the use of solid food or sucrose does not appear to account for negative incentive contrast effects.

Magnitude of incentive contrast as a function of amount of verbal reward change

In Experiment 1 a decrease in incentive magnitude resulted in negative incentive contrast effects, which were a positive function of the amount of verbal reward reduction. In Experiment 2 an increase in amount of reward produced positive incentive contrast effects, which were, as in Experiment 1, a monotonic function of the amount of reward change.

Effects of an increment in monetary incentive magnitude on instrumental responding and repeated increases in reward magnitude in humans

Human Ss performed at a reliably higher level for a tone previously paired with an increase in monetery incentive magnitude and consequent positive incentive contrast effects than did individuals for a tone previously associated with the larger control groups’s quantity of incentive. In Experiment 2, upward incentive contrast effects which resulted from a single increment in magnitude of monetery reinforcement were eliminated in individuals who experienced the increase in amount of money after an upshift in reward amount. These data are consistent with the notion that positive incentive contrast effects in human Ss are due to some form of appetitive motivational state.

Magnitude of human incentive contrast as a function of amount of training and age

In Experiment 1, increased amounts of preshift training produced larger negative contrast effects in human Ss; in Experiment 2, positive contrast was a monotonic function of amount of preshift training with humans. Experiment 3 demonstrated that negative contrast which occurs subsequent to a reduction in incentive size with older individuals, is eliminated in younger people; and, finally, Experiment 4 showed that upward contrast effects found with older individuals do not occur with younger Ss. It appears that magnitude of incentive contrast effects in humans is a positive function of amount and length of preshift training. It also seems that age of the S is a variable which controls the occurrence of human incentive contrast effects.

Effects of a reduction in reward magnitude on active avoidance behavior in humans

Human Ss actively avoided a tone previously paired with a decrease in monetary incentive magnitude and consequent negative contrast effects more often than did individuals the tone associated with the control group’s lower quantity of reward. These data agree with the notion that at the human level, negative incentive contrast effects are explainable in terms of an aversive motivation response.

Increase in incentive amount with verbal reinforcement

An increase in the amount of verbal reinforcement resulted in gradual, as opposed to sudden, increases in behavior and no evidence of positive incentive contrast effects. These results with human Ss agree with the data obtained from animal Ss and suggest that a shift in incentive size in humans affects learning as opposed to some more temporary mechanism.