Harlow wanted to study the mechanisms by which newborn rhesus monkeys bond with their mothers. These infants were highly dependent on their mothers for nutrition, protection, comfort and socialization. What, exactly, though, was the basis of the bond?
The behavioral theory of attachment would suggest that an infant would form an attachment with a carer that provides food.
In contrast Harlow’s explanation was that attachment develops as a result of the mother providing “tactile comfort", suggesting that infants have an innate (biological) need to touch and cling to something for emotional comfort.
Harry Harlow did a number of studies on attachment in rhesus monkeys during the 1950's and 1960's. His experiments took several forms:
1. Infant monkeys reared in isolation – some died, others were frightened and behaved in an abnormal manner. They could not interact with other monkeys even when they were older.
2. Infant monkeys reared with surrogate mothers – 8 monkeys were separated from their mothers immediately after birth and placed in cages with access to two surrogate mothers, one made of wire and one covered in soft terry toweling cloth. Four of the monkeys could get milk from the wire mother and four from the cloth mother. The animals were studied for 165 days.
Both groups of monkeys spent more time with the cloth mother (even if she had no milk). The infant would only go to the wire mother when hungry. Once fed it would return to the cloth mother for most of the day. If a frightening object was placed in the cage the infant took refuge with the cloth mother (its safe base).
This surrogate was more effective in decreasing the youngsters fear. The infant would explore more when the cloth mother was present. This supports the evolutionary theory of attachment, in that it is the sensitive response and security of the caregiver that is important (as apposed to the provision of food).
The behavioral differences that Harlow observed between the monkeys who had grown up with surrogate mothers and those with normal mothers were;
- They were much more timid.
- They didn’t know how to act with other monkeys.
- They were easily bullied and wouldn’t stand up for themselves.
- They had difficulty with mating.
- The females were inadequate mothers.
Harlow concluded that for a monkey to develop normally s/he must have some interaction with an object to which they can cling during the first months of life (critical period). Clinging is a natural response - in times of stress the monkey runs to the object to which it normally clings as if the clinging decreases the stress.
Harlow found therefore that it was social deprivation rather than maternal deprivation that the young monkeys were suffering from. When he brought some other infant monkeys up on their own, but with 20 minutes a day in a playroom with three other monkeys, he found they grew up to be quite normal emotionally and socially.