2007 年 25 巻 2 号 p. 181-186
The within-session decrease in the speed of operant responding by rats was investigated for every reinforcement which was delivered. Eighteen rats in the continuous reinforcement (CRF) group responded to the CRF schedule until 121 reinforcements were obtained in each session. Eighteen rats in a variable interval (VI) group responded to a VI 15-second schedule until 101 reinforcements were obtained in each session. A clock-dependent VI schedule (Snapper, Shimoff, & Schoenfeld, 1971) was used to steadily provide reinforcements, regardless of any change in the response rate. The data from the last 12 of 15 sessions were analyzed. The inter-reinforcement time was observed to increase within CRF sessions. In contrast, the inter-reinforcement time remained at approximately 15 seconds within VI sessions. In both of the groups the response speed (the number of responses per second) was well described as a linear function of the number of reinforcements obtained. The response speed therefore decreased in proportion to the increase in the number of reinforcers within the sessions.