Semester

Summer

Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Psychology

Committee Chair

Michael Perone

Abstract

Differential-reinforcement-of-low-rate (DRL) and differential-reinforcement-of-high-rate (DRH) schedules specify a certain pace of responding eligible for reinforcement. The present study assessed the value of a paced schedule of reinforcement using a concurrent-chains schedule. Pigeon's pecks on the left and right initial-link keys led to one of two terminal-link VI 60-s schedules, programmed on the center key. Completion of a terminal-link schedule always led to access to grain. The value of a terminal-link schedule was measured by the initial-link choice proportions. In the baseline, pecks on either initial-link key produced access to one of two unpaced terminal-link schedules every 60 s, on average. In subsequent experimental conditions, a paced and unpaced terminal-link was available. In the paced conditions restrictions were placed on interresponse times (IRTs) that would be eligible for reinforcement. These restrictions were based on a percentile of baseline IRT distribution. For the DRH conditions, IRTs had to be shorter than the 25th percentile of the distribution and for the DRL conditions IRTs had to be longer than the 75th percentile of the distribution. These durations were adjusted using a changing criterion design. Pacing contingencies had effects on initial and terminal link behavior. Terminal-link response rates were raised above baseline rates in the DRH conditions, and were lowered below baseline rates in the DRL conditions. Three of four pigeons showed an increase in choice for the unpaced schedule when compared to baseline, indicating an increase in value for the unpaced schedules. An analysis of the reinforcement and choice ratios indicate that these differences in value were not due to differences in reinforcement rate.

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