Some effects of procedural variations on choice responding in concurrent chains

Abstract

The present research used pigeons in a three-key operant chamber and varied procedural features pertaining to both initial and terminal links of concurrent chains. The initial links randomly alternated on the side keys during a session, while the terminal links always appeared on the center key. Both equal and unequal initial-link schedules were employed, with either differential or nondifferential terminal-link stimuli across conditions. The research was designed to neutralize initial- and terminal-link spatial cues in order to gain a clearer understanding of the roles of conditioned reinforcement and delayed primary reinforcement in choice. With both equal and unequal initial links and with differential terminal-link stimuli, all pigeons reliably preferred the chain with the shorter terminal link. However, with equal initial links and nondifferential stimuli, all pigeons were indifferent. With unequal initial links and nondifferential stimuli, some pigeons were also indifferent, while others actually reversed and preferred the chain with the shorter initial link, even though it was followed by the longer terminal link. The decrease if not reversal of the previous preferences implies that preferences in concurrent chains are a function of the conditioned reinforcement afforded by terminal-link stimuli, rather than delayed primary reinforcement.

Keywords: choice; concurrent chains; conditioned reinforcement; delay of reinforcement; key peck; pigeons.

Fig 1

The design of the principal comparisons in the two experiments. The initial links always appeared on the side keys, and across conditions the schedules could be equal or unequal. The terminal links always appeared on the center key, and across conditions the terminal-link stimuli could be differential or nondifferential. Each experiment involved a different procedure for arranging the initial links.

Fig 2

The choice proportions in favor of chain VI 30 s FI 10 s when pitted against chain VI 30 s FI 20 s using the procedure of Experiment 1. The data are presented for each pigeon, when the terminal-link stimuli were differential (Diff) and nondifferential (Non), and are the averages of the individual conditions in Table 1.

Fig 3

The choice proportions in favor of chain VI 20 s FI 10 s when pitted against chain VI 10 s FI 20 s using the procedure of Experiment 1. The data are presented for each pigeon, when the terminal-link stimuli were differential (Diff) and nondifferential (Non), and are averages of the individual conditions in Table 1.

Fig 4

Terminal-link response rates in Experiment 1 from conditions with equal VI 30-s initial links. The figure shows the rates of responding in the FI 10 s terminal link, and in the first and second halves of the FI 20 s terminal link, with differential stimuli (top panel) and a nondifferential stimulus (bottom panel) in the terminal links. The data are presented for each pigeon, and are averages of the individual conditions in Table 1.

Fig 5

Terminal-link response rates in Experiment 1 from conditions with unequal initial links. The figure shows the rates of responding in the FI 10 s terminal link, and in the first and second halves of the FI 20 s terminal link, with differential stimuli (top panel) and a nondifferential stimulus (bottom panel) in the terminal links. The data are presented for each pigeon, and are averages of the individual conditions in Table 1.

Fig 6

The choice proportions in favor of chain VI 30 s FI 10 s when pitted against chain VI 30 s FI 20 s using the procedure of Experiment 2 (equal initial links). The data are presented for each pigeon, when the terminal-link stimuli were differential (Diff) and nondifferential (Non), and are averages of the data from the individual conditions reported in Table 2.

Fig 7

The choice proportions in favor of chain VI 20 s FI 10 s when pitted against chain VI 10 s FI 20 s using the procedure of Experiment 2 (unequal initial links). The data are presented for each pigeon, when the terminal-link stimuli were differential (Diff) and nondifferential (Non), and are averages of the data from the individual conditions reported in Table 2.

Fig 8

Terminal-link response rates in Experiment 2 from conditions with equal VI 30-s initial links. The figure shows the rates of responding in the FI 10 s terminal link, and in the first and second halves of the FI 20 s terminal link, with differential stimuli (top panel) and a nondifferential stimulus (bottom panel) in the terminal links. The data are presented for each pigeon, and are averages of the individual conditions in Table 2.

Fig 9

Terminal-link response rates in Experiment 2 from conditions with unequal initial links. The figure shows the rates of responding in the FI 10 s terminal link, and in the first and second halves of the FI 20 s terminal link, with differential stimuli (top panel) and a nondifferential stimulus (bottom panel) in the terminal links. The data are presented for each pigeon, and are averages of the individual conditions in Table 2.