Behavioral Contrast on Mixed Schedules

Keypecking by 4 pigeons was studied on mixed schedules of reinforcement. Positive behavioral contrast was found when the schedule was shifted from Mixed VI VI to Mixed VI Extinction only when the VI schedule value was small relative to the component duration.

Behavioral Contrast during the Acquisition of Speechreading

Two hearing-impaired children were taught to speechread the names of 18 objects divided into three sets. A multiple baseline across sets of objects was obtained for each subject. Tokens presented contingent upon correct responses to certain sets of names increased the frequencies of those correct responses. Both subjects exhibited positive behavioral contrast during the acquisition of speechreading; correct responses to one set increased above the previously established level when the contingencies for a second set changed from token reinforcement to extinction. The obtained contrast effect was conducive to learning and the procedure was effective in teaching the children to speechread the training words.

Behavioral Contrast in Pigeons with Qualitatively Different Reinforcers

Three white Carneaux pigeons were trained to respond on a mult VI 1-min. (milo reinforcement), VI 1-min. (pea reinforcement) schedule when each component was associated with a different key, feeder, and reinforcer. The experiment was divided into four phases. In Phases 1 and 3, baseline rates of responding were established. In experimental Phases 2 and 4, one component of the multiple schedule was changed to extinction. During the experimental phases, response rates decreased in the extinction component and increased in the unchanged component (positive behavioral contrast). The increase in responding in the unchanged component was greater when the more valued reinforcer was extinguished. These findings are very similar to those reported by Beninger and Kendall (1975) and extend the positive contrast effect to another species, pigeons.