Singer, R.A., Berry, L.M. & Zentall, T.R. (2007).
Preference for a stimulus that follows a relatively aversive event: contrast or delay reduction?
Journal of the Experimental Analysis of Behavior, 87, 275-285.
Several types of contrast effects have been identified including incentive contrast, anticipatory contrast, and
behavioral contrast. Clement, Feltus, Kaiser, and Zentall (2000) proposed a type of contrast that appears to be
different from these others and called it within-trial contrast. In this form of contrast the relative value of
a reinforcer depends on the events that occur immediately prior to the reinforcer. Reinforcers that follow
relatively aversive events are preferred over those that follow less aversive events. In many cases the delay
reduction hypothesis proposed by Fantino (1969) also can account for such effects. The current experiments
provide a direct test of the delay reduction and contrast hypotheses by manipulating the schedule of
reinforcement while holding trial duration constant. In Experiment 1, preference for fixed-interval (FI) versus
differential-reinforcement-of-other-behavior (DRO) schedules of reinforcement was assessed. Some pigeons
preferred one schedule over the other while others demonstrated a position (side) preference. Thus, no
systematic preference was found. In Experiment 2, a simultaneous color discrimination followed the FI or DRO
schedule, and following training, preference was assessed by presenting the two positive stimuli simultaneously.
Consistent with the contrast hypothesis, pigeons showed a significant preference for the positive stimulus that
in training had followed their less preferred schedule.
Key words: : within-trial contrast, contrast, stimulus preference, delay reduction, cognitive dissonance, key peck, pigeons