Three groups of two rats each were given 300, 900, or 1500 water reinforcements for responses separated by at least 6 sec (DRL 6 sec). When reinforcement was subsequently withheld, resistance to extinction was generally low for all Ss, although there was some indication that it increased with the number of previous reinforcements. When reinforcement was again programmed, very rapid reconditioning was found for all Ss. The data are discussed in terms of the discriminative function of the reinforcing stimulus.Ferster & Skinner (1957) have emphasized the possibility of differentially reinforcing a rate of response. With a DRL 6 sec schedule, for example, it is possible to condition low rates by reinforcing successive responses only when they are separated by an interresponse time (IRT) of at least 6 sec. The present paper examines the characteristics of DRL behavior during extinction and reconditioning following 300, 900, or 1500 reinforcements.Subjects. The Ss were six experimentally naive, male Sprague-Dawley albino rats, approximately 180 days old at the start of experimentation. For a week before the fust experimental session, and also after the extinction session, the Ss were given 10 min access to water at the same time each day.After sessions in which water reinforcements were obtained, the Ss were limited to 5 min access to water in the home cage, where food was always avai1able.Apparatus. The experimental chamber was a Skinner box (Grason-Stadier, Model E3125A) containing a single lever. The chamber was modified so that a solenoid-operated dipper, normally in the up position, was briefly displaced downward into a reservoir and delivered 0.02 cc of water whenever a lever press met the criterion for reinforcement. From a room adjacent to the experimental chamber, standard relay apparatus automatically programmed the reinforcement contingencies, while responses and reinforcements were recorded by counters and a clH!lulative recorder (Gerbrands, Model C-2).Procedure. On the day after operant level determination and dipper approach training, bar-pressing was conditioned by reinforcing successively closer approximations to the complete response. During this session each of the fust 2(}'30 complete bar-presses was reinforced. A 6-sec DRL contingency was then introduced and the session was continued until the rat had obtained 100 additional reinforcements. Subsequent training sessions under the same 6-6ec DRL schedule were terminated after 100 reinforcements.Since operant levels for all rats ranged from 24 responses in 30 min, Ss were assigned to groups randomly. Two rats were extinguished after 300 reinforcements, two after 900 reinforcements, and two after 1500 reinforcements. Extinction, during which bar-presses did not activate the dipper, occurred in a single 3-h session given on the day following the fmal DRL session. On the day after extinction, all Ss were reconditioned on the original DRL schedule until 100 reinforcements had been obtained.Results and Discussion. The baseline response rates averaged over ...
