Initial-link duration and acquisition of preference in concurrent chains

Abstract

Initial-link response allocation in concurrent chains becomes less extreme as the absolute duration of the initial links increases (Fantino, 1969). The present study asked whether initial-link duration affected how quickly response allocation reached asymptote (i.e., acquisition of preference). Six pigeons were trained on a concurrent-chains procedure in which the terminal links were fixed-interval (FI) 8 sec FI 16 sec or FI 16 sec FI 8 sec and were reversed every 20 sessions. Across conditions, all possible combinations of transitions between variable-interval (VI) 8-sec (short) and VI 24-sec (long) initial-link schedules were studied. Overall, the rate of acquisition was faster when the durations of the initial links preceding the reversal were short rather than long, and when the durations of the initial links following the reversal were long rather than short. By contrast, initial-link duration had no effect on acquisition or asymptotic measures of temporal control of terminal-link responding. These results support the core principle of delay-reduction theory (Fantino, 1969) that the impact of a conditioned reinforcer varies directly with initial-link duration, but also suggest that temporal learning during the terminal links proceeds independently ofinitial-link duration.

A Decision Model for Steady‐state Choice in Concurrent Chains

“…Specifically, studying how response allocation changes when the terminal‐link schedules are altered—that is, the dynamics of choice—may lead to a model that not only accounts for changes in response allocation, but makes accurate steady‐state predictions as well. In the present article, we show that the decision model proposed by Grace and McLean (2006) and Christensen and Grace (2008) to account for acquisition phenomena leads to an expression for the effects of terminal‐link schedules on steady‐state choice. In brief, the model assumes that when food is obtained in a terminal link, subjects make a discrimination—a decision—about whether the delay from terminal‐link onset to food was relatively short or long.…”

“…Grace and McLean (2006) noted that these results—particularly the lack of disruption in Experiment 2—were potentially problematic for models of choice based on conditioned reinforcement. If response allocation depended on the learned value of the terminal‐link stimuli, then it should have been easier for choice to adjust in Experiment 1, where the right terminal link changed between two values, than in Experiment 2, where the right terminal link was sampled from a potentially infinite population of values.…”

“…Overall, the relationship appeared to be sigmoidal, with a greater difference between the clusters than within them (see their Figure 4). Grace and McLean (2006) suggested that a process akin to categorical discrimination may have influenced responding—that is, the pigeons learned to respond more in each session to whichever alternative led to the shorter terminal link delay, but how much that delay was shorter than the alternative had little influence over choice.…”

“…Grace and McLean (2006) proposed a model which could account for the different patterns of results in the maximum‐variation condition. They assumed that after reinforcement in a terminal link, pigeons made a decision about whether the preceding reinforcement delay was short or long relative to a criterion.…”

“… Grace and McLean (2006) proposed a decision model for acquisition of choice in concurrent chains which assumes that after reinforcement in a terminal link, subjects make a discrimination whether the preceding reinforcer delay was short or long relative to a criterion. Their model was subsequently extended by Christensen and Grace (2008, 2009a, 2009b) to include effects of initial‐ and terminal‐link duration on choice.…”