LEARNING AND MOTIVATION 6, l-10 ( 1975) The Effect of S- on Observing Behavior RAY BLANCHARD Uniuersity of Illinois at Urbana-Champaign Eight pigeons were run on a one-key, discrete-trials observing pro- cedure. Pecks during a trial produced S’ and S-, colored key lights which signalled whether the trial would end with response-independent grain re- inforcement or nonreinforcement. S’ and Sm were produced on a VI sched- ule which began operating at the onset of the trial. In the main experi- mental condition, only a response preceded by at least G set of nonresponding could produce S- on nonreinforced trials; any response which satisfied the VI requirement produced S’. on reinforced trials. This pro- cedure allowed the birds to produce S’ on reinforced trials with or with- out producing S- on nonreinforced trials. The subjects learned to produce fewer S-s over sessions, indicating that S had a punishing effect on observ- ing. The results were taken as evidence for the conditioned reinforcement hypothesis of observing and against the uncertainty reduction hypothesis. In a common observing response procedure, an animal’s observing be- havior results in the exposure of one of a pair of stimuli correlated with the availability (or probability) of primaly reinforcement. The stimulus exposed when reinforcement is available is designated S+; the stimulus exposed when reinforcement is unavailable, S-. The availability of rein- forcement itself is not altered by the observing behavior. The maintenance of observing behavior under such a procedure is readily demonstrated ( Hendry, 1969a). Two explanations have been offered to account for the maintenance of observing behavior. These agree in assuming that observing is rein- forced by the production of S+, but disagree in predicting the effect of S- upon a response which produces it. The conditioned reinforcement The experiment reported here forms part of a doctoral dissertation submitted to the University of Illinois at Urbana-Champaign. The research was supported by a National Science Foundation grant (GB 21447) to David A. Lieberman. The author wishes to thank Dr. Lieberman for repeated advice and encouragement throughout the course of the experiment. Requests for reprints should be addressed to the author, Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada. 1 Copyright @ I975 by Academic Press, Inc. All rights of reproduction in any form reserved.