An infant Rhesus monkey (Macaca mulatta) in a cage during an animal experiment. Maternal deprivation experiments performed by Harry Harlow of the University of Wisconsin in the 1950's involved separating infant monkeys from their mothers and rearing them with surrogate mothers made of wire or cloth. The monkeys were kept in partial or total isolation, in wire cages or in "pits" or "wells of despair." These experiments found that comfort, security and affection are necessary for a monkey's healthy psychosocial development.