William A. Mason

Group formation by rhesus monkeys

Abstract 1. 1. Eleven rhesus monkeys, including juvenile and adult animals of both sexes, were selected to approximate a small natural group and their social activities were recorded during the initial period in which they were together as a group. 2. 2. Clearly differentiated status relationships were immediately apparent between major subgroups, and in many instances between individuals within subgroups, as indicated by patterns of aggressive and submissive behaviour and sexual activity. 3. 3. These findings suggest that for the socially experienced monkeys used in the present experiment, status was determined principally by the perception of the physical attributes, posture and bearing of companions, rather than by a contest of strength.

Activity patterns of rhesus monkeys in a social group

Abstract A group of 11 rhesus monkeys was selected to approximate a small natural group. Observations were made on a variety of social and individual activities. The effects on group activity of manipulation of the feeding situation and of diurnal factors was determined. Major activities of the group included: resting, grooming, huddling, travelling, and auto-activities. The last comprised feeding, drinking, object manipulation, and self-grooming. Sex, aggression, play, and vocalization combined accounted for less than 3 per cent. of the activity observed. Individuals were in the proximity of other animals almost two-thirds of the time. The group was observed to spend more than 75 per cent. of the day in above-ground locations. Temperature was correlated with the frequencies of grooming, resting, and with physical locations. The concept of flight and fight distances seems helpful in explaining the distance and relations between specific individuals and the changes these undergo in relation to specific circumstances. With appropriate replication and with extension to new genera this approach may be expected to supply quantitative measures to aid in the behavioural differentiation of primate taxa.

Communication between young rhesus monkeys

Abstract 1. 1. The communication performance of 12 rhesus monkeys was investigated in a situation in which the rewards of both members of a pair of monkeys could not exceed chance levels unless the operator monkey responded to cues provided by the informant monkey which indicated the location of food. Each member of the pair was trained in both operator and informant roles in different phases of the experiment. Communication performance improved progressively to levels consistently above chance. However, communication learning appeared to be specific to the role in which the individual was trained, and when roles were reversed no evidence of transfer was obtained. Tests of foodsharing behaviour showed a substantial increase in the tendency to share food with the partner following communication training. This occurred however, only when the partner was the only social stimulus present; if another monkey was also present there was no evidence of preferential responses to the partner. In all phases of communication training, monkeys which were housed together performed more efficiently than did monkeys housed individually. 2. 2. The acquisition of stimulus-producing responses was investigated by causing an opaque screen to remain in front of the informant unless the operator monkey pulled a vertical lever at the front of its restraining cage. Initially, operators responded immediately to the foodcarts, but with further testing there was a steady increase in the tendency to defer the response to the food-carts until the lever had been pulled, revealing the informant monkey. 3. 3. Transfer of communication training was tested with new monkey informants, and with two inanimate stimuli, a mechanical puppet, and a stationary plaque. The latter two objects were placed behind the rewarded food-carts before each trial. There was clear evidence of positive transfer to each of these conditions, but marked differences among conditions were obtained. Performance with the monkeys averaged 76 per cent. correct, as compared with 62 and 40 per cent., with the puppet and the plaque, respectively. 4. 4. To test the ability of trained operator monkeys to select the appropriate informant on the basis of behavioural cues, the communication situation was arranged so that two informant monkeys were present on all trials. However, on any trial only one of these informants could be rewarded, and the operators rewards were contingent upon delivering food to this informant. Efficiency of discrimination began at approximately 45 per cent, (chance = 25 per cent. and improved progressively to levels above 75 per cent.

Sex Differences in Affective-Social Responses of Rhesus Monkeys

1. These researches investigated the stereotyped affective-social responses of adult male and female rhesus monkeys to human observers and to a situation designed to produce conflict. 2. In the first experiment threat responses to the human observer were scored on a four point scale by three observers working independently. Each observer obtained significantly more frequent and intense threat reactions from female than from male subjects. 3. In a second experiment, food was presented in proximity to an aversive stimulus and records were obtained of threat reactions, lipsmacking, fear grimaces, and food acceptance. Females displayed significantly more threat responses and fear grimaces. Differences between sexes in lipsmacking and food acceptance were in the expected direction, but were not statistically significant.

SOCIAL DEVELOPMENT OF RHESUS MONKEYS WITH RESTRICTED SOCIAL EXPERIENCE

For a short period following birth the infanc macaque monkey is in continuous contact wich its mother. Soon, however, it begins to leave her for brief periods and under close maternal surveillance, makes short excursions into the surrounding environment. If the infant s h o ~ ~ l d stray too far or a disturbance arise, the mother retrieves it at once. In time the mother becomes more tolerant of such excursions and the infant spends progressively more of its waking hours away from her, engaged in play with other young animals. The infant still seeks the mother, however, when it is hungry, fatigued or frightened, and she continues to go to it when danger threatens (Altmann, 1962; Jensen & Tolman, 1962; Lashley &Watson, 1913; Nolte, 1955; Tinklepaugh & Hartman, 1932). The transition from total dependence on the mother to limited independence probably involves changes in maternal responsiveness, as well as complementary changes in infant motivations and accivities. A third factor which may affect this process is the presence of ocher individuals and the nature of their reactions to the ~n fan t . Presumably these variables jointly determine the shift in infant behavior from patterns which are predominantly mother-oriented toward those which are directed toward peers. The present report is concerned with the social development of infant rhesus monkeys whose social experience was restricted and controlled. Ss were reared apart from their mothers and were permitted physical contact with other monkeys only in the experimental situation.

Conditions Influencing Vocal Responsiveness of Infant Chimpanzees

Infant chimpanzees were tested to determine the effects on distress vocalizations (whimpering, screaming) of stimulus conditions approximating the physical relationship to the mother. Under such conditions spontaneous vocalizations were infrequent, and vocal responsiveness to a painful stimulus was substantially reduced.

Initial Responses of Infant Rhesus Monkeys to Solid Foods

Naturalistic observations of infant monkeys living with their mothers indicate that, although nursing may continue for 18 months or longer, ingestion of small quantities of solid food begins as early as the first postnatal month (Carpenter, 1934; Lashley and Watson, 191 3; Watson, 1914; Zuckerman, 1932 ). Although the factors determining initial responsiveness of free ranging primates to solid foods have never been investigated experimentally, it is probable that the onset and direction of initial reactions to solid foods are determined by multiple variables including observational learning, social facilitation, the development of sensori-motor capabilities, the availability of particular foods, and the effectiveness of these substances as incentives to visual, manual, and oral exploration. The use of Ss that are removed from the mother at birth and raised under conditions which control social contacts and prevent casual encounters with edible solids, permits assessment of each of these factors and evaluation of its influence upon initial responses to solid foods. Previous experiments have demonstrated the importance of exploration incentives for adult rhesus monkeys (Harlow, 1953) and have shown that the infant macaque, less than a month of age, displays strong and persistent motivation to explore its environment visually and manually (Harlow, Blazek, and McClearn, 1956). Presumably, edible substances when first encountered by monkeys raised in the laboratory are functionally similar, if not equivalent, to novel nonedible stimuli, and reactions to solid foods should be influenced by the stimulus characteristics, including diversity and heterogeneity, that are effective in eliciting exploratory behaviors (Welker, 1956). The present experiment investigates the responsiveness of infant rhesus monkeys, with no previous experience with solid foods, to a uniform array of food incentives, an array in which the incentives differ in color-brightness, and an array in which the incentives vary in multiple dimensions including colorbrightness, texture, taste, and nutritive characteristics.

Development of communication between young rhesus monkeys.

A communication situation is described in which the rewards of both members of a pair of monkeys cannot exceed chance levels unless the operator monkey responds to cues provided by the informant monkey which indicate the location of food. Performance under these test conditions improved progressively to levels consistently above chance.

Learned Approach by Infant Rhesus Monkeys to the Sucking Situation

One of the earliest responses of the newborn mammal is that of sucking, a response elicited by a wide variety of stimuli but most vigorously by the tactual-thermal-gustatory pattern of stimuli provided by milk and the nursing situation. Because sucking is a highly persistent response and because it is one of the first skeletal-muscle responses to mature, it has been used as the dependent variable for measuring early human learning, as in the study by Kantrow ( 1 ). Furthermore, since sucking is obviously adaptive, continues for considerable time in the higher mammals, and by its nature promotes physical contiguity between mother and child, some theorists, including Sears, et al. ( 3 ) and Mussen and Conger ( 2 ) , have assigned a uniquely important role in psychological development to learning occurring in the nursing situation. The present experiment measured the approach performance of the monkey to the nursing situation rather than the conditioning of the nursing response. The actual dependent variable was the total-body locomotion elicited presumably by the expectation of milk, expectation being defined as the learned adient or avoidant tendencies appropriate to a particular incentive. The Iocomotor response, unfortunately, matures less rapidly than the sucking response, and this factor may delay the demonstration of very early learning. On the other hand the approach response, as contrasted with sucking, has the advantage of ease and reliability of measurement. In addition to investigating the learning of approach to the sucking situation, tests were conducted to assess possible generalized adient tendencies acquired by stimuli associated with the nursing situation.