Observing responses and serial stimuli: searching for the reinforcing properties of the S-

Abstract

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. 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.

Keywords: clock stimuli; conditioned reinforcement; lever pressing; observing responses; rats.

Fig 1

A diagram of the core elements of the procedure. The squares on the left diagram exemplify the optional clock procedure scheduled during the five subintervals of the EXT components and during the reinforcement component. The different intermittencies of the tone are illustrated with vertical bars within each subinterval. To differentiate the reinforcement component stimuli it was illustrated with an unfilled circle. Responses on the left lever produced reinforcement during the reinforcement component and had no consequences during the EXT component. The clock was not available unless an observing response (R_O) occurred on the right lever in which case the corresponding stimulus was presented for 5 s. The dotted horizontal lines exemplify the moment in which the clock could start. The right diagram illustrates the procedure with only one S− during the subintervals of the EXT component.

Fig 2

Mean relative number of observing responses during successive subintervals of the EXT component and during the reinforcement component across six successive five-session blocks. The upper panels show the data for the subjects that were exposed to the optional clock procedure and the lower panels show the data for the subjects in the control group.

Fig 3

Mean rate of food responses during the stimuli for each successive subinterval of the EXT component and during the reinforcement component across six successive five-session blocks. See description of Figure 2.

Fig 4

Mean relative number of observing responses during successive subintervals of the EXT component and during the reinforcement component across the five successive blocks of five sessions. The upper panels show the data for the subjects that were exposed to the optional clock procedure and the lower panels show the data for the subjects in the control group.

Fig 5

Mean rate of food responses during the stimuli for each successive subinterval of the EXT component and during the reinforcement component across the five blocks of five sessions. See description of Figure 4.