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.

/pdf/incentive-contrast-a-review-of-behavioral-changes-following-1z6b6o4pl3.pdf

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

Free food or earned food? A review and fuzzy model of contrafreeloading

Animals will perform an operant response to obtain food when abundant free food is available. These data have implications for current learning theories, especially in terms of the motivational variables associated with such behavior. The present paper reviews the literature and provides an analysis that suggests that responding for food in the presence of free food is importantly controlled by stimulus change attendant upon response-dependent food presentation. This apparent stimulus-reinforcer effect on behavior is compared to that observed in other areas of animal learning research that include preference between schedules of response-dependent and response-independent reinforcement, preference between schedules of signaled and unsignaled reinforcement, autoshaping and automaintenance, and self-reinforcement in animals.

/pdf/the-free-food-contrafreeloading-phenomenon-a-review-and-4j2fg4tm2u.pdf

The free food (contrafreeloading) phenomenon: A review and analysis

Partial reinforcement: A selective review of the alleyway literature since 1960.

Partial reward either following or preceding consistent reward: A case of reinforcement level.

Shifts in percentage of reinforcement viewed as changes in incentive.

2 groups of 60 rats received either 75 or 285 runs in a runway before being given a choice between freeloading from a dish of pellets in the start box or running the maze for a single pellet The 285-trial Ss showed less willingness to perform the operant than the 75-trial Ss This is opposite to what Jensen (1963) had found in the Skinner box Schedule of reinforcement (100 vs 50%) during training did not significantly affect freeloading scores

Calvin M. Leung

Papers

Shifts in percentage of reinforcement viewed as changes in incentive.

"Freeloading" in a runway as a function of amount of training and type of reinforcement schedule.