Escobar, R. & Bruner, C.A. (2009).
Observing responses and serial stimuli: Searching for the reinforcing properties of the S-.
Journal of the Experimental Analysis of Behavior, 92, 215-231.
The control exerted by a stimulus associated with an extinction component (S-) on observing responses was determined as a function of its temporal
relation with the onset of the reinforcement component (S+). Lever pressing by rats was reinforced on a mixed random-interval extinction schedule.
Each press on a second lever produced stimuli associated with the component of the schedule in effect. In Experiment 1 a response-dependent clock
procedure that incorporated different stimuli associated with an extinction component of a variable duration was used. When a single S- was presented
throughout the extinction component, the rate of observing remained relatively constant across this component. In the response-dependent clock
procedure, observing responses increased from the beginning to the end of the extinction component. This result was replicated in Experiment 2, using
a similar clock procedure but keeping the number of stimuli per extinction component constant. We conclude that the S- can function as a conditioned
reinforcer, a neutral stimulus or as an aversive stimulus, depending on its temporal location within the extinction component.
Key words: observing responses, conditioned reinforcement, clock stimuli, lever pressing, rats