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Mother-infant separation in rhesus monkeys
Journal of Psychosomatic Research. Vol. 16, pp. 221 to 228. Pergamotl Press, 1912. Printed in Great Britain
MOTHER-INFANT
SEPARATION IN RHESUS MONKEYS* R. A. HINDER
THAT
a temporary or permanent separation of a human child from its mother may have far-reaching effects on its development is now widely accepted. But the severity of the effects, how they can be ameliorated, the bases of the wide individual variation which occurs and the crucial factors involved, are still largely unknown. Since an experimental approach is not possible with human subjects, the possibilities of using monkeys instead has been investigated [l-6]. In our experiments the animals are kept in groups of a male, 2-4 females and their young, in outside cages 5.5 m long, communicating with an inside room. In the initial experiments, mothers of infants 20-32 weeks old were removed to a distant room for 6 or 13 days and then replaced. During the separation period the infants showed a high frequency of “whoo” distress calling, and reduced locomotor activity, and they spent a considerable amount of time sitting or shuffling about in a hunched depressed posture. When the mothers were returned the infants were at first very clinging, leading to more rejection by the mothers. The symptoms shown by the infants during separation continued in a reduced form for some time after reunion but had largely disappeared after a few weeks in most infants [2]. Tests 6 months and 2 yr after the separation experience revealed some differences between infants which had and had not had such a separation experience in their responses to strange objects or mildly frustrating situations in the home pen. The differences were much more marked when testing was carried out in a strange environment. It thus appears that a brief separation can have (direct or indirect) long-lasting effects on infant behaviour [3]. The effects of the separation experience on the infant during the weeks after reunion were more marked if the separation lasted 13 days than if it lasted only 6 days [4]. In both cases, however, there was marked individual variation. There was a slight tendency for male infants to be affected more than females, but the most important factor in this individual variation appeared to be the nature of the mother-infant relationship. While the degree of distress shown was little related to the amount of time that the infants spent on or near their mothers, it was most marked in those infants that were frequently rejected by their mothers and that played a large role in maintaining proximity with them. The infants’ symptoms of distress immediately after reunion were more highly correlated with the pre-separation values of these aspects of the mother-infant relationship than with the contemporaneous ones, but with time the pre-separation relationship became less important and the contemporaneous one more so. Of course, correlations do not prove that the mother-infant relationship determines the amount of stress shown, but it seems likely [5]. * These studies were carried out in collaboration with various colleagues-most particularly the late Dr. Yvette Spencer-Booth, Miss Lynda Davies and Mrs. C. Perkis. The data have been or are being published clsewhcre: to prevent duplication, they are presented here in summary only. j’ M.R.C. Unit on the Development and Integration of Behaviour, Madingley, Cambridge. 227
R. A.
228
HINDE
In more recent experiments (Hinde and Davies, in preparation) we have compared the effects of removing the mother to a distant pen for 13 days, the infant remaining where it is, with those of removing the infant, the mother remaining in the home pen. Although the infant-removed infants showed considerable distress during the separation period, they showed much less distress during the weeks following reunion than did the mother-removed infants. A variety of explanations for this are possible, but it seems probable that the smaller degree of disturbance suffered by the mothers of the infant-removed infants is an important factor. Correlations between measures show that, during the post-separation period, day-to-day changes in mother-infant interaction are largely due to changes in the mother [6], and we have already seen that the infant’s distress is related to the nature of the mother-infant relationship. With an infant-removed infant, the mother, the prime determiner of the relationship, suffers less trauma and is presumably (though we have not measured this yet) less disturbed than the mother of the mother-removed infant. It is probably for this reason that mother-infant interaction and infant behaviour return more rapidly to normal after reunion in the infant-removed infants than in the mother-removed ones. On this view, the resulting disturbance of the mother-infant relationship is a central issue in the separation experience.
REFERENCES HINUE R. A. and SPENCER-BOOTH Y. Effects of brief separation from mothers on rhesus monkeys. 172, 111-118 (1971). SPENCER-BOOTH Y. and HINDE R. A. Effects of 6 days separation from mother on 18- to 32-week old rhesus monkeys. Anim. Be/w., 19, 174-191 (1971). HINDE R. A. and SPENCER-BOOTH Y. Effects of brief separations from mothers during infancy on behaviour of rhesus monkeys 6-24 months later. J. Child Psychol. Psychiut., 12, 157-172. SPENCER-BOOTH Y. and HINDE R. A. The effects of 13 days maternal separation on 30-32 week-old rhesus monkeys compared with those of shorter and interrupted separation. Anim. Behav., 19, Science,
595405.
5. HDJDE R. A. and SPENCER-BOOTH Y. to a period of separation from their 6. HINDE R. A. Analysing the roles of relations in Rhesus macaques. Ann. N.
Individual differences in the responses of rhesus monkeys mothers. J. Child Psycho/. Psychiutr. 11, 159-176 (1970). the partners in a behavioural interaction-Mother-infant Y. Acad. SC., 159, 651-667
(1969).
MOTHER-INFANT
SEPARATION IN RHESUS MONKEYS* R. A. HINDER
THAT
a temporary or permanent separation of a human child from its mother may have far-reaching effects on its development is now widely accepted. But the severity of the effects, how they can be ameliorated, the bases of the wide individual variation which occurs and the crucial factors involved, are still largely unknown. Since an experimental approach is not possible with human subjects, the possibilities of using monkeys instead has been investigated [l-6]. In our experiments the animals are kept in groups of a male, 2-4 females and their young, in outside cages 5.5 m long, communicating with an inside room. In the initial experiments, mothers of infants 20-32 weeks old were removed to a distant room for 6 or 13 days and then replaced. During the separation period the infants showed a high frequency of “whoo” distress calling, and reduced locomotor activity, and they spent a considerable amount of time sitting or shuffling about in a hunched depressed posture. When the mothers were returned the infants were at first very clinging, leading to more rejection by the mothers. The symptoms shown by the infants during separation continued in a reduced form for some time after reunion but had largely disappeared after a few weeks in most infants [2]. Tests 6 months and 2 yr after the separation experience revealed some differences between infants which had and had not had such a separation experience in their responses to strange objects or mildly frustrating situations in the home pen. The differences were much more marked when testing was carried out in a strange environment. It thus appears that a brief separation can have (direct or indirect) long-lasting effects on infant behaviour [3]. The effects of the separation experience on the infant during the weeks after reunion were more marked if the separation lasted 13 days than if it lasted only 6 days [4]. In both cases, however, there was marked individual variation. There was a slight tendency for male infants to be affected more than females, but the most important factor in this individual variation appeared to be the nature of the mother-infant relationship. While the degree of distress shown was little related to the amount of time that the infants spent on or near their mothers, it was most marked in those infants that were frequently rejected by their mothers and that played a large role in maintaining proximity with them. The infants’ symptoms of distress immediately after reunion were more highly correlated with the pre-separation values of these aspects of the mother-infant relationship than with the contemporaneous ones, but with time the pre-separation relationship became less important and the contemporaneous one more so. Of course, correlations do not prove that the mother-infant relationship determines the amount of stress shown, but it seems likely [5]. * These studies were carried out in collaboration with various colleagues-most particularly the late Dr. Yvette Spencer-Booth, Miss Lynda Davies and Mrs. C. Perkis. The data have been or are being published clsewhcre: to prevent duplication, they are presented here in summary only. j’ M.R.C. Unit on the Development and Integration of Behaviour, Madingley, Cambridge. 227
R. A.
228
HINDE
In more recent experiments (Hinde and Davies, in preparation) we have compared the effects of removing the mother to a distant pen for 13 days, the infant remaining where it is, with those of removing the infant, the mother remaining in the home pen. Although the infant-removed infants showed considerable distress during the separation period, they showed much less distress during the weeks following reunion than did the mother-removed infants. A variety of explanations for this are possible, but it seems probable that the smaller degree of disturbance suffered by the mothers of the infant-removed infants is an important factor. Correlations between measures show that, during the post-separation period, day-to-day changes in mother-infant interaction are largely due to changes in the mother [6], and we have already seen that the infant’s distress is related to the nature of the mother-infant relationship. With an infant-removed infant, the mother, the prime determiner of the relationship, suffers less trauma and is presumably (though we have not measured this yet) less disturbed than the mother of the mother-removed infant. It is probably for this reason that mother-infant interaction and infant behaviour return more rapidly to normal after reunion in the infant-removed infants than in the mother-removed ones. On this view, the resulting disturbance of the mother-infant relationship is a central issue in the separation experience.
REFERENCES HINUE R. A. and SPENCER-BOOTH Y. Effects of brief separation from mothers on rhesus monkeys. 172, 111-118 (1971). SPENCER-BOOTH Y. and HINDE R. A. Effects of 6 days separation from mother on 18- to 32-week old rhesus monkeys. Anim. Be/w., 19, 174-191 (1971). HINDE R. A. and SPENCER-BOOTH Y. Effects of brief separations from mothers during infancy on behaviour of rhesus monkeys 6-24 months later. J. Child Psychol. Psychiut., 12, 157-172. SPENCER-BOOTH Y. and HINDE R. A. The effects of 13 days maternal separation on 30-32 week-old rhesus monkeys compared with those of shorter and interrupted separation. Anim. Behav., 19, Science,
595405.
5. HDJDE R. A. and SPENCER-BOOTH Y. to a period of separation from their 6. HINDE R. A. Analysing the roles of relations in Rhesus macaques. Ann. N.
Individual differences in the responses of rhesus monkeys mothers. J. Child Psycho/. Psychiutr. 11, 159-176 (1970). the partners in a behavioural interaction-Mother-infant Y. Acad. SC., 159, 651-667
(1969).