In previous papers, the author concluded that spontaneous alternation resulted from the interaction of the processes of facilitation and inhibition which waxed and waned in different phases and at different speeds.
The present experiment was undertaken to find the effects of the number of repetition of forced trials and of time intervals between the last forced trial and the test run, both upon the facilitatory and inhibitory processes in spontaneous alternation.
A simple T-maze was used. After exploration and pretraining, 60 naive albino rats were divided into three groups which differed in the number of forced trials in the direction of the first free choice ; these were 0, 4 and 9 respectively. All rats were tested four times in each of 10 time intervals, i. e. 0, 10, 30, 60, 120, 210, 300, 450, 600 and 900 seconds, in random order during 20 experimental days. Results :
1) The per cent alternation decreased in all groups as the the interval increased. However, the manners of decrement differed in each group (Fig. 1). In group I (no forced trial) the score was not lower than the chance line which was determined on the basis of the position habit of rats, while the alternation of group II (four forced trials) decreased below the chance line and then returned to it. In group III (nine forced trials) the high score of alternation continued for 900 seconds.
2) Comparing three groups, the four forced trials were found to decrease the tendency to alternate, while nine forced trials increased it. The above results seemed to confirm the hypothesis proposed by the author in the previous papers.
3) The higher the per cent alternation, the longer the running time at the trial immediately before the test run, excepting for group I (Fig. 3).
4) The running times on tests, however, indicated that the higher the alternation, the shorter the running time (Fig. 2). This reverse relationship suggested that the inhibitory effects were related to the choice direction.
From the results and the other related phenomena, it was concluded that the facilitatory effects was closely related to reinforcement, and the inhibitory effect was the one imposed on the central nervous system by all kinds of stimulation. It was assumed that Hull's reactive inhibition would not be the peripheral state of drive, but the central state of the proprioceptive stimulation which had the properties of inhibitory drive and cue.
Both the response-avoidance theory and the stimulus-avoidance theory would not go beyond the issue : that is, which one of the stimuli, internal or external, had the dominant cue value for the rat.
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