Behavioral contrast in pigeons and rats: A comparative analysis

Abstract

The effects of reinforcement rate on behavioral contrast were examined in pigeons and rats. Each species was exposed to a series of 12 multiple variable-interval schedules, divided into four 3-schedule series. Each series consisted of a standard contrast manipulation, and baseline schedules provided a different rate of reinforcement in each of the series. The functions relating reinforcement rate to the magnitude of contrast were different across species. Rats showed a U-shaped function, with reliable contrast occurring only at high reinforcement rates. Pigeons showed an inverted U -shaped function, with contrast occurring on all schedules except the schedule providing the lowest rate of reinforcement. Pigeons discriminated between schedule components better than rats did, although differences in discrimination were probably not responsible for the differences in contrast. The results suggest that behavioral contrast in rats may be a different phenomenon from behavioral contrast in pigeons. The results cannot be explained by current theories, which view contrast as the product of a single general process.

Habituation to the Reinforcer May Contribute to Multiple‐schedule Behavioral Contrast

“…First, it is incomplete because it cannot account for all observations of contrast. However, there is broad agreement that contrast is multiply determined (e.g., de Rose, 1986;Dougan, Farmer-Dougan, & McSweeney, 1989;Dougan et al, 1985Dougan et al, , 1986Hassin-Herman, Hemmes, & Brown, 1992;Williams, 1983), a view that is supported by explicit evidence. As we have argued, some evidence shows that contrast occurs in the absence of differential habituation when the conditions of reinforcement in the following component are changed.…”

Dynamic changes in the size of behavioral contrast.

“…To determine if positive and negative contrast occurred, percent deviation from baseline scores were calculated by dividing the rate of responding in the constant component during the contrast phase by the rate of responding in this component during the averaged baseline phase, multiplying the result by 100 and then subtracting 100. Such a transformation normalizes the data and has been used as an index of contrast in other studies (see Dougan, Farmer-Dougan & McSweeney, 1989). Deviation scores were calculated for each subject.…”

Behavioral contrast: Research and areas for investigation

“…The vast majority of research on contrast has been conducted with nonhumans, specifically pigeons (Dougan, Farmer‐Dougan, & McSweeney, ). Of the research on contrast with human subjects, most has been human‐operant in nature (i.e., with arbitrary, non‐socially significant behavior), and only ratio‐based schedules have been used.…”