Positive contrast as a function of component duration using a within-session procedure

Pigeons pecked keys for food reinforcers delivered by multiple schedules. Three experiments examined changes in the size of positive contrast with changes in component duration. They used a within-session procedure which measured rates of responding during the baseline and contrast phases within the same session. Contrast was largest for shorter components, a result similar to that found using traditional procedures. Therefore, the present results provide preliminary support for the use of the within-session procedure to study contrast. They also showed that the inverse relation between key-peck contrast and component duration is a robust finding which survives major changes in procedure. Finally, they suggest that different functions relate the size of contrast to component duration for key pecking and treadle pressing.