Date of Graduation

2003

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Behavioral Medicine and Psychiatry

Committee Chair

Michael Perone

Committee Co-Chair

Kennon A. Lattal

Committee Member

Cynthia M. Anderson

Committee Member

Stanley H. Cohen

Committee Member

Kristine Krajnak

Abstract

Transitions from rich-to-lean conditions of reinforcement often produce extended pausing in operant responding and may underlie maladaptive behavior in natural settings. Reducing their disruptive effects is of basic and applied interest. Experiment 1 assessed the effects of the overall reinforcement rate on pausing. Pigeons were exposed to a multiple fixed-ratio (FR) 50 FR 100 schedule. The number of rich (FR 50) and lean (FR 100) components varied across conditions. Pausing during the rich-to-lean transition was inversely related to the overall rate of reinforcement for two of three pigeons. As the number of rich components comprising the multiple schedule increased, pausing decreased. In Experiment 2, three pigeons were exposed to a multiple FR FR schedule whose components differed in reinforcer magnitude. Across conditions, the accuracy of the stimulus correlated with the small-reinforcer cue was degraded by occasionally delivering large reinforcers following signaled large-to-small transitions. Across a wide range, degrading the accuracy of the small cue had no systematic effect on pausing, although local effects were observed. In Experiment 3, four pigeons were exposed to a multiple FR FR schedule whose components differed in reinforcer magnitude. Stimuli associated with the past reinforcer were presented along with stimuli correlated with the upcoming reinforcer. Experiment 3 attempted to attenuate the role of the past reinforcer by (a) occasionally presenting an inaccurate past-reinforcer cue, and (b) inserting blackouts between components. These manipulations had no systematic effect on pausing. The results are interpreted in terms of response strength; the role of conditioned reinforcement is discussed; and parallels with successive negative contrast are drawn. Applications to natural settings are discussed. In general, pausing during negative shifts in reinforcement context appears to be highly resistant to change.

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