The purpose of the present investigation was to study the problem of what is learned in discrimination reversal learning. In experiment I, 6 Japanese monkeys were trained on object discrimination problems. Each problem consisted of three stages; original learning, prereversal experience and reversal learning. The original learning continued to a criterion of 18 out of 20 correct responses, followed by 10 additional trials. There were three conditions of prereversal experience; N-P, P-N and C (control). For condition N-P, Ss received 10 rewarded prereversal trials to the object that had initially been negative but which was to be positive during the subsequent reversal trials : and, conversely, for the condition P-N, Ss received 10 non-rewarded trials to the object that had initially been positive but which was to be negative during the reversal. For the control condition, Ss received no prereversal experience between the original and the reversal learning. Each S was given 3 problems, involving different prereversal experience. The order of the presentation of the 3 problems was different by Ss and was determined according to a latin square. The experiment consisted of the duplication of the above procedure, using the same Ss, with the interval of about 7 months.
Performance of each S on each problem is shown in table 1. Analysis of variance of number of errors during reversal learning revealed superior performance in conditions N-P and P-N to the control condition. The results support the duoprocess theory which emphasizes the effects of both reward and nonreward. In experiment II, 30 kindergarden children, 46 years old, were tested on pattern discrimination problems. After the preliminary problem, Ss received the main problem, which consisted of three stages; original learning, prereversal experience and reversal learning. After each S reached the criterion of 10 consecutive correct responses in the original learning, he received 4 trials of the prereversal experience, which were different by groups. Ss of group N-P, group P-N, and the control group received the corresponding prereversal experience, followed by the reversal learning. The results in Table 2 show the superior reversal performance of Ss of group N-P, to that of Ss of the other 2 groups. They support the uniprocess theory which emphasizes the effect of reward. The results of the above two experiments on Japanese monkeys and children, along with the previous data on rats and squirrel monkeys, reveal the systematic species differences in the nature of reversal learning.

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By stimulating some points of brain limbic system, various consummatory or motivational behaviors are elicited. These points are often identical with intracranial self-stimulation (ICS) points. In fact, hypothalamic stimulation which evoked feeding, drinking, or sexual behavior, produced ICS. In the present experiment, two tests were made for further investigation of the relationship between ICS and motivational behavior.
13 rats with a chronically implanted bipolar electrode in, or neighbouring MFB were used in self-stimulation test and 10 of them in observation test. Electrical stimulus used was 50 c/s alternate current. The apparatus were a modified Skinner box (Fig. 1) for the self-stimulation test and an observation box for the observation test. The latter box consisted of a large box and a small one, and contained food, water, paper stripes, wooden chips, and one female rat which was brought into estrus by subcutaneous injection of estradiol and progesterone.
In the self-stimulation test, after the Ss learned to press the lever for maximum 0.5 sec. brain stimulus, latency of the lever press and the lever press rate during 3 minutes were determined for each of 10 stimulus intensity levels from 10 to 100 μA for three days. In the observation test, behaviors of the rats were recorded every 10 seconds for 4 days (Table 1). On every test day, 10 minutes operant level of behavior was recorded before stimulation test period. In the stimulation test period, stimulus-ON 1 min. or 2 min. alternated stimulus-OFF 1 min. or 2 min and current increased in an ascending order from 10 μA to 100 μA in 10 μA steps. The stimulus given during the stimulus-ON period was either continuous or repetitive (train duration 0. 5 sec., interstimulus interval 0. 5 or 1. 5 sec.). After the experiment had been completed, 7 Ss were sacrificed and electrode loci determined.
Results were as follows :
1. All rats which pressed the lever more than 60 times per 3 minutes, showed exploratory behavior (EB, Table 1) as evoked behavior in the observation test (Table 1).
2. Increase in stimulus intensity resulted in increase in percentage of EB. On the other hand, sexual behavior which was sometimes aroused at lower current intensities, as well as grooming behavior tended to be inhibited at higher intensities (Fig. 3, Table 3.)
3. For 2 of 3 non-self-stimulater, EB was elicited. While one of these two revealed to be a self-stimulater, when tested again in the Skinner box, the EB pattern of the other rat (still non-self-stimulater) seemed different from those of the self-stimulaters (Table 2, Fig. 3).
4. In the self-stimulation test, frequently, the response rate did not increase or even showed some decrement at higher current levels (Fig. 2). But as the latency remained short, this decrement can not be ascribed to the decline of the reinforcing power of the strong stimulus.
In conclusion, EB evocation seems to have some relation to ICS. This result corresponds with the recent studies sugg esting the importance of the readiness property of evoked behavior.

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[in Japanese]

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[in Japanese]

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