Harry Frederick Harlow was an American psychologist best known for his maternal-separation, dependency needs, and social isolation experiments on rhesus monkeys, which manifested the importance of caregiving and companionship to social and cognitive development. He conducted most of his research at the University of Wisconsin–Madison, where humanistic psychologist Abraham Maslow worked with him for a short period of time.
Harlow's experiments were controversial; they included creating inanimate surrogate mothers for the rhesus infants from wire and wool. Each infant became attached to its particular mother, recognizing its unique face and preferring it above others. Harlow next chose to investigate if the infants had a preference for bare-wire mothers or cloth-covered mothers. For this experiment, he presented the infants with a clothed "mother" and a wire "mother" under two conditions. In one situation, the wire mother held a bottle with food, and the cloth mother held no food. In the other situation, the cloth mother held the bottle, and the wire mother had nothing.