The effects of separating rhesus monkey infants from their mothers for six days.

(1) The mothers of four rhesus monkey infants, living in small social groups, were removed for 6-days when the infants were 30-32-weeks-old. Records were made of various aspects of mother-infant interaction and infant behaviour before, during and after the separation period. (2) During separation the animals' behaviour changed considerably, and could be described as "depressed". They gave a higher number of who calls than before separation, and showed less locomotor and play activity. Over the course of the separation period they became active for more of the time, but they showed less intense activity during those periods in which they were active at all. (3) When the mother was returned all four infants spent more time on their mothers than before separation. The effect was more marked, the more time the infant had spent on its mother before the experiment. The relations between the various response measures suggested complex interactions between the demands of the infant and the tolerance of the mother during the period after her return. (4) The more severe effects of the deprivation experience disappeared in a few days after the mothers' return in two of the infants, but were present for at least some months in the others. All four infants showed some effects during the rest of the first year of life. (5) During separation the infants investigated strange objects less, and responded more strongly to frightening stimuli, than when the mother was present. (6) The effects of separation shown by these infants were somewhat similar to those seen in human children who have had the same sort of experience.