Developmental Processes of Timing Behavior in mult FR DRL and mult FR DRO Schedules of Rats

Abstract

Some developmental processes of timing behavior have been observed as the modification of a series of operant responses and some other collateral responses under several temporal reinforcement schedules, partic-ulary under DRL and DRO schedules (2, 7, 11, 12).The present study was designed to investigate such processes of timing behavior under the mult FR DRL and the mult FR DRO schedules, respectively. the Ss were 16 male rats of the in-bred Wister strain. They were experimentally naive and approximately 150 days old at the start of the experiment, weighing from 225g with a mean of 253g. After a feeding schedule of 7 days in which food intake was limited to maintain their body weights at about 85% of that in the ad-lib feeding condition, rats were adapted to a standard Skinner box having a response bar and a food tray, within a sound-attenuating room. The next day they were shaped to barpress for a 45mg food pellet for every bar pressing, and trained on a typical CRF schedule for the following 2 days. Thereafter, they were divided into two homogeneous groups of 8 rats. One group was trained with mult FR 5 DRL 8, and the other with mult FR 5 DRO 8. In these procedures, every session was composed of the same 3 replications having an FR component of 3 min, a TO of lmin, a DRL or DRO of 7 min, and a TO of 1 min, respectively. Therefore, every session time was 35min. The turning of a signal lamp and the presenting of a tone were used as the discriminative stimuli between the FR component and the DRL or the DRO component. The following day, each group was divided again into two homogeneous subgroups; the mult FR 5 DRL 8 group was divided into the mult FR 10 DRL 8 and the mult FR 10 DRL 20 groups, the mult FR 5 DRO 8 group into the mult FR 10 DRO 8 and the mult FR 10 DRO 20 groups. The training sessions for these four groups were continued once a day for 30 consecutive days.The main findings were as follows. The number of responses in each FR component, was gradually increased through the training sessions, but without significant group differences (Fig. 1). The distribution of pause time after the reinforced responses in FR 10 components did not show very many distinctive differences between groups or training sessions (Fig. 2). Fig. 3 indicates the number of responses in the DRL or the DRO components. The differences between groups were not so clear, although all groups decreased their responses with the lapse of the training course. The number of reinforced responses in the DRL or the DRO components was differed significantly in DRL or DRO time used, in the training sessions, and also in the reinforcement schedules applied. Furthermore, some interactions were found (Fig. 4). Fig. 5 and Fig. 6 show the IRT distributions obtained by the most typical individuals in the DRL and the DRO components. According to the training sessions carried out, the distributions of post SR intervals in DRO 8 and DRO 20 changed gradually to a more suitable direction for those reinforcement schedules (Fig. 7). The differences and the similarities of timing behavior between DRL and DRO schedules were discussed, and some advantages of experiments using the mult schedules to investigate timing behavior were suggested.