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Undergraduate Research Project Management System

Effects of Variability in Delay to Reinforcement on Within-Session Decreases in Operant Responding

Status Complete
Seeking Researchers No
Start Date 05/25/2012
End Date 05/29/2012
Funding Source Discovery Grant
Funding Amount
Community Partner
Related Course
Last Updated 03/25/2012 02:19PM


  Eric Murphy

Student Researchers
  Alyssa Hoskie, Amanda Hesser, Mikaela Mulder, Shea Lowery


Abstract 1

Our study investigated the hypothesis that habituation to food reinforcement occurs more slowly when the delay to reinforcement is variable rather than constant. To test this hypothesis. Four Wistar rats lever pressed on a fixed interval 8-s (FI) schedule of reinforcement to earn five 45 mg food pellets during 30 min sessions. In the constant condition. the delay to reinforcement was 10
s during each reinforcer delivery. During the variable condition, the reinforcers were delayed by either 1 or 19 s (M= 10 s). Rates of responding were higher and within-session decreases in responding were more attenuated during the variable delay condition. Our results indicate that reinforcer effectiveness can be increased or decreased depending upon the variability in the delay to reinforcement. These findings are generally consistent with the idea that habirnation (e.g., McSweeney & Murphy. 2009) accrues to food reinforcers and may have implications for behavioral treatments in applied settings.

Abstract 2

The present experiment tested the hypothesis that habituation contributes to within—session decreases in operant responding. In particular. we tested for the variety effects property of habirnation which states that habituation should develop more slowly and overall responsiveness should be higher when reinforcers are presented in a variable, rather than in a constant manner. The experimental design was a 2 (Amount: constant vs. variable 5 food pellets) X 2 (Schedule: fixed interval 8-s vs. variable interval 8-s schedule of reinforcement). Four rats responded on either a FI 8- or a VI 8-s schedule in which pressing a lever produced a constant amount of 5
food pellets or an average of 5 (1 or 9 with a probability of .50) food pellets per delivery dining 30 min daily sessions. When both amount and schedule of reinforcement were constant. rates of responding were lower and within-session decreases in responding were steeper than when one or both reinforcement parameters were variable. These preliminary data suggest that varying one or more reinforcement parameters increases the effectiveness of a repeatedly presented reinforcer. The results of the experiment are consistent with the idea that habituation to the reinforcer contribute to within—session changes in operant responding.

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