Experimental animal. Rhesus monkey infant clutches a cloth diaper. Maternal deprivation experiments performed by Harry Harlow of the University of Wisconsin in the 1950's involved separating infant monkeys from their mothers, rearing them with "surrogate" mothers made of wire or cloth, in partial isolation in wire cages, or total isolation in "pits" or "wells of despair." These experiments found that comfort, security, and affection are necessary for healthy psychosocial development.