Psychological distance to reward: The aversiveness of the first component stimulus in a chain

Pigeons served in two experiments examining the aversiveness of the first-component stimulus (S1) in a fixed-time (FT) chained schedule using a two-key escape procedure. Responding on a chain key was reinforced by a chained schedule while pecking a switch key produced brief blackouts on the chain key. In Experiment 1, pigeons were first trained on a chain FT 30 s FT 30 s (i.e. overall duration 60 s) using the chain key alone (Phase I); then they were allowed to turn off the chain-key light by pecking the switch key without affecting reinforcement programmed by the chained schedule (Phase II); finally, the blackout contingency on the switch key was discontinued (Phase III). Results showed that pigeons pecked the switch key only during C1 but not C2 and this behavior was maintained only when the pecks produced blackouts of S1 (Phase II). Hence escaping from C1 was negatively reinforcing and the phenomenon was attributed to the aversiveness of S1. Experiment 2 assessed the effect of the overall duration of the chained schedule on switch-key responses using the same procedure. With the three durations investigated (20 s, 40 s and 60 s), results showed that the switch-key rate was a positive function of the overall duration. Thus the aversiveness of S1 increased as the duration lengthened. These findings are consistent with those from choice studies in that segmentation of a schedule extends its 'psychological distance to reward'.