Thesis Defense: 'Effects of Variability in Duration and Delay of Reinforcement on Food-Responding in Rats' by Whitney Bakarich, March 3

Monday, March 3, 2:30-4 p.m. Social Sciences Building, Room 223

Whitney Bakarich, master's candidate in the Clinical Psychology Program at UAA, will defend her thesis, "Effects of Variability in Duration and Delay of Reinforcement on Food-Responding in Rats."

Abstract: Understanding the variables that maintain reinforcer effectiveness has important implications for basic research to inform applied behavior analysis. The goal of the study was to investigate the combined effects of rate of reinforcement and variability in duration and delay on within-session changes in operant responding in two experiments. In each experiment, Wista rats lever pressed for liquid sucrose on three fixed interval (FI) schedules of reinforcement. In Experiment 1, subjects lever pressed for liquid sucrose by either a constant or varied duration of access to reinforcement. In Experiment 2, subjects were exposed to a constant or variable delay of reinforcement. Each experiment was a 2 (Condition: constant or variable reinforcement) X 3 (Rate of reinforcement: FI 8-s, 16-s and 32-s) X 12 (2.5-minute interval) counterbalanced design. Results showed two fundamental properties of behavior undergoing habituation: stimulus rate and variety effects. First, within-session decreases in responding were steeper (greater habituation) at higher rates (e.g., FI 8-s) than lower rates (e.g., FI 32-s). Second, within-session rates of responding declined slower (slower habituation) when access to the reinforcer was presented in a variable versus constant manner. Because habituation occurs for both ingestive and noningestive stimuli, the present study adds to the body of literature on habituation and can inform clinical practice on the variables that sustain operant behavior through varying the delivery of the reinforcer.