How Monkeys Acquire a New Way of Seeing

In an experiment on perceptual learning, monkeys were given the opportunity to watch on television the ‘private behaviour’ of another monkey (which did not know it was being watched). The subjects were shown monkey X for twenty sessions in a row, followed by monkey Y for twenty sessions, followed by monkey X again for twenty sessions. The subjects' ‘interest’ in the stimulus monkey remained roughly level within each block of twenty sessions, but increased in a step-like way at the changeover from X to Y, and again from Y to X. These results are interpreted as evidence that the subjects gained little or no extra insight into the nature of private behaviour through watching the same monkey in successive sessions; the critical factor in their perceptual education was the comparison between one monkey's behaviour and another's.

Pairwise Dominance and Social Preference in Squirrel Monkeys

5 male and 5 female squirrel monkeys, previously dominance tested, were observed in a noncompetitive social preference situation. Following nonsocial adaptation trials, all possible pairs of monkeys were observed, one pairmate serving as S and the other as a stimulus animal in a free-choice preference test. Ss' latencies to enter the apparatus and activity levels were greatly reduced by the addition of social partners. While social choices were largely uninfluenced by the dominance of the stimulus animal, the sex of the stimulus monkey proved to be an effective variable in that females elicited more approach behaviors than males. These results are consistent with previous studies of squirrel monkeys' preferences measured in noncompetitive social situations.

Some Causal Factors in Autogrooming Behaviour of Adult Stump-Tailed Macaques (Macaca Arctoides)

The causal relationship among autogrooming, close proximity, and locomotion are studied experimentally in dyads of adult Stumptailed Macaques (Macaca arctoides). The experimental apparatus was an oblong cage (alley) composed of six segments (each measuring 70 X 55 X 70 cm). At each end of the alley was a small compartment separated by a plexiglas partition. A female test-monkey was present in the alley, while a male stimulus-monkey was either present in the left or the right compartment or was absent. During a 15 minute observation period, the behaviour of the test-monkey was recorded simultaneously with the segment in which this occurred. The first experiment showed that the presence of a stimulus-monkey induced : - a tendency to stay close to the stimulus-monkey, - an increase in the probability of autogrooming, - a decrease in locomotion. Furthermore, the observations of the situation in which the stimulus-monkey was present, revealed : - a positive correlation between the probability of spending time close to the stimulus-monkey and the probability of autogrooming, both during non-locomotory periods, - a negative correlation between the total locomotion and the probability of autogrooming during non-locomotory periods. After these observations, 3 more experiments arranged in such a way that the results were intercomparable, were carried out. The experimental situations compared were the following: 1. The test-monkey is free in the alley while the stimulus-monkey is present, 2. The test-monkey is free in the alley while the stimulus-monkey is absent, 3. The test-monkey is enclosed in an end segment of the alley while the stimulus-monkey is absent, 4. The test-monkey is enclosed in an end segment close to the stimulus-monkey, 5. The test-monkey is enclosed in an end segment far away from the stimulus-monkey. Enclosing of the test-monkey was accomplished by inserting a plexiglass partition in the alley. Comparison of situation 3, 2, and 1 showed that enclosing increased the probability of autogrooming. The increase was not proportional to the total locomotion that was prevented. Furthermore, the increase was too small to explain the increase caused by the presence of the stimulus-monkey which also reduced locomotion. Comparison of situations 3, 4 and 5 showed that the increase in the probability of autogrooming due to the presence of the stimulus-monkey was very small when the stimulus-monkey was far away and larger when it was close by. Comparison of situation 4, and 1 showed that increasing the time spent close by did not increase the probability of autogrooming. Decreasing the time spent close by (comparing 5, and 1) however, caused a decrease in the probability of autogrooming which was proportional to the decrease in time spent close by. These results lead to the formulation of the following hypothesis: the probability of autogrooming is, increased in a direct way by the time spent close by. The increase occurs only up to a certain optimum value which is determined by an unknown factor. Autogrooming reduces the locomotion in a direct way which in reverse way increases autogrooming in some indirect. Reduction in locomotion increases the time spent close by.