The Effect of Stimulus Adaptation upon the Exploratory Behavior in the Rat (Part 1)

Abstract

It is supposed that the concept of “discrepancy” plays an important role in the discussion of the exploratory behavior. Discrepancy is defined as difference between past stimulation and present stimulation. That is, stimulus change, novelty and complexity are little more than discrepancy. In two experiments reported here, discrepancy was produced by means of stimulus adaptation and it is designed to investigate the effect of the discrepancy upon the exploratory behavior in the rat.
The apparatus used was two-choice situation composed of Room S and Room C. Room C differed from Room S in having more luminosity, checkered pattern and the fixed panels (see Fig. 1). The experiment of each consisted of two stages, i. e. the adaptation period and the exploration period, and had four groups, i. e. Group S, C, SC and NSC. In Experiment 1, Group S was adapted for Room S, Group C for Room C, and Group SC for both Room S and C for 15 min. per day for 5 days. Group NSC was not adapted for the apparatus, but for the detention cage. After 24 hours from the last adaptation, all subjects received free exploration for 10 min. per day for 3 days. In Experiment 2, the subjects were adapted for the apparatus for 75 min. within a day. Immediately after this period, free exploration was allowed for 10 min. for 3 days. Three response measures were used during the exploration period, i. e. starting latency, time spent in Room S and C, and the first choice of the room. In addition, the number of defecation during the adaptation period was measured.
The results were as follows :
1. In both experiments, the number of defecations during adaptation period didn't decrease in Group SC, while the other three groups decreased (Fig. 2 and 5). This fact might suggest that discrepancy aroused emotional response especially in the Group SC in which discrepancy was produced both within a day and between days.
2. The starting latencies decreased as the subjects explored the apparatus in both experiments (Fig. 3 and 6). Especially in Group SC which explored Room S and C during adaptation period the latency was the shortest, while Group NSC which had no experience to explore the apparatus showed the longest latency. This results might also indicate that discrepancy produced emotional behavior in the exploratory situation.
3. In Experiment 1, Group S and SC spent more time in Room S than in Room C, and in Experiment 2, all groups spent more time in Room S (Fig. 4 and 7). It might be suggested from these results that Room C was aversive for the rat. It is to be noted, however, that in Experiment 1 the time spent in Room S decreased in Group S as the subjects explored the situation, but the time spent in Room C increased. It might seem that discrepancy functioned negatively in the first day of free exploration, but later functioned positively.
4. In both experiments Group S changed significantly their first choice from Room S to Room C during exploration period. This result might also suggest ambivalence of discrepancy.