CHOICE AND DELAY OF REINFORCEMENT: EFFECTS OF TERMINAL‐LINK STIMULUS AND RESPONSE CONDITIONS

In two experiments, pigeons were exposed to concurrent‐chains schedules in which a single initial‐link variable‐interval schedule led to access to terminal links composed of fixed‐interval or fixed‐delay schedules. In Experiment 1, an 8‐s (or 16‐s) delay to reinforcement was associated with the standard key, while reinforcer delay values associated with the experimental key were varied from 4 to 32 s. The results of Experiment 1 showed undermatching of response ratios to delay ratios with terminallink fixed‐delay schedules, whereas in some pigeons matching or overmatching was evident with the fixed‐interval schedules. In Experiment 2, one pair of reinforcer delay values, either 8 versus 16 s or 16 versus 32 s, was used. In the first condition of Experiment 2, different delays were associated with different keylight stimuli (cued condition). In the second condition, different terminal‐link delays were associated with the same stimulus, either a blackout (uncued‐blackout condition) or a white key (uncued‐white condition). To examine the role of responses emitted during delays, the keys were retracted during a delay (key‐absent condition) in the third condition and responses were required by a fixed‐interval schedule in the fourth condition. Experiment 2 demonstrated that the choice proportions for the shorter delay were more extreme in the cued condition than in the uncued‐blackout condition, and that the response requirement imposed by the fixed‐interval schedules did not affect choice of the shorter delay, nor did the key‐absent and key‐present conditions. These results indicate that the keylight‐stimulus conditions affected preference for the shorter of two delays and that the findings obtained in Experiment 1 depended mainly on the keylight‐stimulus conditions of the terminal links (i.e., the conditioned reinforcing value of the terminal‐link stimuli).