The effects of terminal-link stimulus arrangements on preference in concurrent chains

Abstract

Pigeons served as subjects in two concurrent-chains experiments in which responding on one or the other of two side keys occasionally produced either a short- (Fl 10-s) or a long- (Fl 20-s) duration terminal-link schedule of food reinforcement according to equal variable-interval 30-s initial-link schedules. In Experiment 1, the terminal link was in effect randomly on either key, or always on the opposite key, in relation to the initial link from which it was entered. In addition, terminal-link stimuli were differential keylights, nondifferential keylights, or differential houselights. Preference tended toward indifference with a random location of a terminal link and nondifferential keylights. However, the birds preferred the shorter terminal link when the terminal link was always in effect on the same key, or always on the opposite key, with either differential or nondifferential keylights. The birds also preferred the shorter terminal link with a random location, nondifferential keylights, and differential houselights. In Experiment 2, the terminal link was always in effect on the center key. As before, terminal-link stimuli were differential keylights, nondifferential keylights, or differential houselights. Preference tended toward indifference with nondifferential keylights. However, the birds preferred the shorter terminal link with either differential keylights or differential houselights. Taken together, the data indicate that terminal-link stimuli in concurrent chains function as conditioned reinforcers, rather than simple discriminative stimuli, although other features of the terminal links such as stimulus location act in concert with the visual stimuli to influence preference.