Harry F. Harlow, Monkey Love Experiments
Harry Harlow with the mother surrogates he used to raise infant monkeys. The terry cloth mother is pictured above. The bare wire mother appears below.
Given a choice, infant monkeys invariably preferred surrogate mothers covered with soft terry cloth, and they spent a great deal of time cuddling with them (above), just as they would have with their real mothers (below).
Surrogate mother experiment
In a well-known series of experiments conducted between 1957 and 1963, researcher Harry Harlow removed baby rhesus monkeys from their mothers, and offered them a choice between two surrogate mothers, one made of terrycloth, the other of wire.
In Harlow's classic experiment, two groups of baby rhesus monkeys were removed from their mothers. In the first group, a terrycloth mother provided no food, while a wire mother did, in the form of an attached baby bottle containing milk. In the second group, a terrycloth mother provided food; the wire mother did not. It was found that the young monkeys clung to the terrycloth mother whether or not it provided them with food, and that the young monkeys chose the wire surrogate only when it provided food.
Whenever a frightening stimulus was brought into the cage, the monkeys ran to the cloth mother for protection and comfort, no matter which mother provided them with food. This response decreased as the monkeys grew older.
When the monkeys were placed in an unfamiliar room with their cloth surrogate, they clung to it until they felt secure enough to explore. Once they began to explore, they occasionally returned to the cloth mother for comfort. Monkeys placed in an unfamiliar room without their cloth mothers acted very differently. They froze in fear and cried, crouched down, or sucked their thumbs. Some even ran from object to object, apparently searching for the cloth mother, as they cried and screamed. Monkeys placed in this situation with their wire mothers exhibited the same behavior as the monkeys with no mother.
Once the monkeys reached an age where they could eat solid foods, they were separated from their cloth mothers for three days. When they were reunited with their mothers, they clung to them and did not venture off to explore as they had in previous situations. Harlow concluded from this that the need for contact comfort was stronger than the need to explore.
The study found that monkeys who were raised with either a wire mother or a cloth mother gained weight at the same rate. However, the monkeys that had only a wire mother had trouble digesting the milk and suffered from diarrhea more frequently. Harlow's interpretation of this behavior, which is still widely accepted, was that lack of contact comfort was psychologically stressful to the monkeys.
The importance of these findings is that they contradicted both the then common pedagogic advice of limiting or avoiding bodily contact in an attempt to avoid spoiling children and the insistence of the then dominant behaviorist school of psychology that emotions were negligible. Feeding was thought to be the most important factor in the formation of a mother-child bond. Harlow concluded, however, that nursing strengthened the mother-child bond because of the intimate body contact that it provided. He described his experiments as a study of love. He also believed that contact comfort could be provided by either mother or father. Though widely accepted now, this idea was revolutionary at the time.
Critics of Harlow's research have observed that clinging is a matter of survival in young rhesus monkeys, but not in humans, and have suggested that his conclusions, when applied to humans, overestimate the importance of contact comfort and underestimate the importance of nursing.
Harlow first reported the results of these experiments in "The nature of love," the title of his address to the sixty-sixth Annual Convention of the American Psychological Association, Washington, D.C., August 31, 1958.
Partial and total isolation of infant monkeys
From around 1960 onwards, Harlow and his students began publishing their observations on the effects of partial and total social isolation. Partial isolation involved raising monkeys in bare wire cages that allowed them to see, smell, and hear other monkeys, but provided no opportunity for physical contact. Total social isolation involved rearing monkeys in isolation chambers that precluded any and all contact with other monkeys.
Harlow et al. reported that partial isolation resulted in various abnormalities such as blank staring, stereotyped repetitive circling in their cages, and self-mutilation. These monkeys were then observed in various settings. Some of the monkeys remained in solitary confinement for 15 years.
In the total isolation experiments baby monkeys would be left alone for three, six, 12, or 24 months of "total social deprivation." The experiments produced monkeys that were severely psychologically disturbed. Harlow wrote:
No monkey has died during isolation. When initially removed from total social isolation, however, they usually go into a state of emotional shock, characterized by ... autistic self-clutching and rocking. One of six monkeys isolated for 3 months refused to eat after release and died 5 days later. The autopsy report attributed death to emotional anorexia. ... The effects of 6 months of total social isolation were so devastating and debilitating that we had assumed initially that 12 months of isolation would not produce any additional decrement. This assumption proved to be false; 12 months of isolation almost obliterated the animals socially...
Harlow tried to reintegrate the monkeys who had been isolated for six months by placing them with monkeys who had been reared normally. The rehabilitation attempts met with limited success. Harlow wrote that total social isolation for the first six months of life produced "severe deficits in virtually every aspect of social behavior." Isolates exposed to monkeys the same age who were reared normally "achieved only limited recovery of simple social responses." Some monkey mothers reared in isolation exhibited "acceptable maternal behavior when forced to accept infant contact over a period of months, but showed no further recovery." Isolates given to surrogate mothers developed "crude interactive patterns among themselves." Opposed to this, when six-month isolates were exposed to younger, three-month-old monkeys, they achieved "essentially complete social recovery for all situations tested." The findings were confirmed by other researchers, who found no difference between peer-therapy recipients and mother-reared infants, but found that artificial surrogates had very little effect.
Harry Harlow's pit of despair
Harlow was well known for refusing to use conventional terminology, and instead choosing deliberately outrageous terms for the experimental apparatus he devised. The tendency arose from an early conflict with the conventional psychological establishment in which Harlow used the term "love" in place of the popular and archaically correct term, "attachment." Such terms and respective devices including a forced mating device he called the "rape rack," tormenting surrogate mother devices he called "Iron maiden," and an isolation chamber he called the "pit of despair". In the latter of these devices, alternatively called the "well of despair," baby monkeys were left alone in darkness for up to one year from birth, or repetitively separated from their peers and isolated in the chamber. These procedures quickly produced monkeys that were severely psychologically disturbed and declared to be valuable models of human depression. Harlow tried to rehabilitate monkeys that had been subjected to varying degrees of isolation using various forms of therapy – with some, yet limited success.
Criticism
Harlow's research, though controversial, has provided insight into the behaviors of abused children and has improved methods of providing care to institutionalized children. While many of his experiments would be considered unethical today, their nature and Harlow's descriptions of them heightened awareness of the treatment of laboratory animals and thus paradoxically contributed somewhat to today's ethics regulations.
Critics have called the results of his research "common sense results": that monkeys, very social animals in nature, when placed in isolation emerge badly damaged, and that some recover and some do not.