Harlow’s Experiments

Perhaps the most famous psychological experiments on animals were

those by Harry Harlow in the 1950’s. Harlow was studying rhesus monkeys

and breeding them in his own laboratory. Initially, he would separate infant

monkeys from their mothers. Later, he discovered that, in spite of receiving

adequate medical care and nutrition, these infants exhibited severe behavioral

symptoms: They would sit in a corner and rock, mutilate themselves,

and scream in fright at the approach of an experimenter, a mechanical toy,

or another monkey. As adolescents, they were antisocial. As adults, they were

psychologically ill-equipped to deal with social interactions: Male monkeys

were sexually aggressive, and females appeared to have no emotional attachment

to their own babies. Harlow decided to study this phenomenon (labeled

“maternal deprivation syndrome”) because he thought it might help

to explain the stunted growth, low life expectancy, and behavioral symptoms

of institutionalized infants which had been documented earlier by René

Spitz.

Results of the Harlow experiments profoundly changed the way psychologists

think about love, parenting, and mental health. Harlow and his colleagues

found that the so-called mothering instinct is not very instinctive at

all but rather is learned through social interactions during infancy and adolescence.

They also found that an infant’s attachment to its mother is based

not on its dependency for food but rather on its need for “contact comfort.”

Babies raised with both a mechanical “mother” that provided milk and a

soft, cloth “mother” that gave no milk preferred the cloth mother for clinging

and comfort in times of stress.

Through these experiments, psychologists came to learn how important

social stimulation is, even for infants, and how profoundly lack of such stimulation

can affect mental health development. These findings played an important

role in the development of staffing and activity requirements for

foundling homes, foster care, day care, and institutions for the aged, disabled,

mentally ill, and mentally retarded. They have also influenced social

policies which promote parent education and early intervention for children

at risk.