Harlow took infant monkeys from their mothers and gave them two inanimate surrogate mothers. One was made from wire and wood, and the other was covered in foam rubber and soft terry cloth.
The infants were appointed to one of two conditions. In the first, the wire mother had a milk bottle and the cloth mother did not. In the second, the cloth mother had the food while the wire mother had none.
Harlow found that the infant monkeys spent more time with the terry cloth mother than the wire mother. When only the wire mother had food, the babies came to the wire mother to feed and immediately returned to cling to the cloth surrogate.
The infants turned to the surrogate mothers for comfort in new situations. When placed in a new setting with a surrogate mother, they would explore, run back to their 'mother' when startled, before exploring again.
Without a surrogate mother, the infants were paralyzed with fear. If a noise-making toy was placed in the cage, an infant with a surrogate mother present would explore and attack the toy; without a surrogate mother, the infant would cower in fear.
Together, these studies produced evidence for the primacy of the parent-child attachment relationship and the importance of maternal touch in infant development