Semester

Spring

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Psychology

Committee Chair

Michael Perone

Committee Co-Chair

Karen Anderson

Committee Member

Elizabeth Kyonka

Committee Member

Tracy Morris

Committee Member

Bernard Schreurs

Abstract

Timeout from avoidance is an effective reinforcer, but the reason is not firmly established. Rats responded on concurrent schedules of avoidance and timeout. Pressing the right lever postponed shocks according to a schedule with a response-shock interval of 30 s and a shock-shock interval of 5 s, and pressing the left lever produced 2-min timeouts according to a variable-interval 45-s schedule. To assess the roles of shock-frequency reduction, response-effort reduction, and signals in varying the reinforcing efficacy of timeout, three experiments were conducted. In Experiment 1, to assess the point at which the reinforcing efficacy of the timeouts would be degraded, the probability of a timeout with shock was increased across conditions. Lower probabilities of shock in timeouts led to relatively small decreases in timeout responding for two of the rats and the maintenance of timeout responding for one rat, while higher probabilities led to more substantial decreases. In Experiment 2, the potential discriminative function of the temporal locations of shock in a yoking procedure from a previous study was investigated in two yoking conditions. In the Local-Yoking condition, there was no short-term change in the rate of shocks from time-in to timeout. The number and temporal location of shocks in the 2-min timeout duplicated the number and temporal location of shocks in the 2 min of time-in preceding the timeout. In the Random-Local-Yoking condition, the number of shocks in timeout duplicated the number of shocks in time-in, but the shocks were delivered in a random temporal position in the timeouts. Timeout responding was maintained at baseline levels for most of the rats in both conditions. In Experiment 3, the role of signals before shocks in restoring the reinforcing efficacy of timeout was investigated. After timeout responding was degraded in Experiment 1, in the subsequent condition, tones were added before the shocks in timeout. The addition of signals before shocks in timeout restored the reinforcing efficacy of the timeouts. The results from the present study suggest that multiple factors may be responsible for the reinforcing efficacy of timeout.

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