Acquisition of bar-pressing under interval and ratio-schedules in the presence and absence of stimuli correlated with water delivery

Abstract

After one-session shaping, eight rats were exposed to interval or ratio schedules in the absence and attenuation of the usual dispenser-based stimuli correlated with the delivery of water, and eight rats to normal delivery water conditions. Half of the rats were exposed to a (fixed-interval) FI 1-min schedule; the other half was exposed to a (fixed-ratio) FR 10 schedule of water reinforcement. Experimental phases consisted of two exposures to an FI or FR schedule interpolated with one (continuous reinforcement) CRF schedule, and a final (fixed-time) FT period. Rats did not show typical scallop-like or break-and-run patterns of responding. Rats responded more in the absence of reinforcement delivery correlated stimuli during the CRF interpolated phase than rats in the presence of such stimuli. Responding and obtained reinforcers were higher during the CRF schedule than under the FI and FR schedules. Responding during the FT period was similar to that in the prior FI or FR phase. The results are discussed in terms of the central role of transitions from CRF reinforcement in order to achieve high rates and characteristic patterns of FI and FR schedules.