The effects of external stimulation at feeding on the amount of activity in the white rat

Abstract

In experiment I, procedure used was similar to Sheffield's except that extinction trials were added. Ss of the experimental group (N=16) were placed in an activity wheel, which was covered with wood box having a flicker light and a feeding mechanism in it. Then the flicker light having the frequency of 1 c/s was presented. After 10 min. the light was turned off and Ss were fed for 60 min., after which they were detained in the apparatus for 30 min. without any stimulus. Ss of the control group (N =16), which were matched to those of the experimental group on the level of activity exhibited in pretraining, were given the same training except that the order of lighting and feeding was exchanged, and the feeding started 10 min. after the onset of each trial. Training was composed of one trial a day for 9 consecutive days. After that, three days of test was given, which consisted of 10 min. lighting followed by 20 min. detention without feeding.
Records were taken for the amount of revolutions of the activity wheel, in which the unit of measurement was one fifth of 360° revolution.
In training trials, as shown in Fig. 2 and 3, the amount of activity of the experimental group in the lighting phase was larger than that of the control group both in the lighting phase and in the pre-feeding phase ; in the experimental group, the amount of activity was larger in the lighting phase than in the non-lighting phase ; in each trial for the experimental group the amount of activity in the lighting phase increased as it came close to the feeding phase. And these tendencies were more conspicuous at the later stage of training.
In test trials, as shown in Fig. 4, the amount of activity of the experimental group in each trial increased gradually during the lighting phase, achieved a peak at about 10 min. after the onset of the trial, and then decreased, in contrast with monotonous decrease shown by the control group.
In experiment II, the order of lighting and feeding was the same as in experiment I, but lighting time, the amount of food in each presentation, and the number of paired presentation of light and food were different. Lighting time was 20 sec. (cf : 10 min. in exp. I), the amount of food in each feeding was limited to 250 mg. (cf food was given ad lib. in each trial in exp. I), and the number of paired presentation of light and food for one day was 10 (cf : 1 in exp. I). Rats were trained 3 days and tested one day.
The results of experiment II, as seen in Fig. 5, differed from those of experiment I in training trials. The amount of activity of the experimental group did not differ significantly from that of the control group through the whole training series, and the amount of activity of both the control and the experimental group decreased as the training proceeded in each day. But in test trial, as seen in Fig. 6, again the tendencies of the experimental and the control group were similar to those in test of experiment I.
We discussed those facts as evidences supporting the hypothesis presented by Sheffield. It seemed that this hypothesis could explain many facts exhibited in ordinary training and extinction process, especially in extinction ; for example, “irrelevant response” suggested by McKintosh, “Humphreys effect” after partial reinforcement, as it was tried by Hulse & Stanley, can be explained by this hypothesis.