Harry Frederick Harlow (October 31, 1905 – December 6, 1981) was an American
psychologist best known for his maternal-separation, dependency needs, and
social isolation experiments on rhesus monkeys, which demonstrated the
importance of care-giving and companionship in social and cognitive development.
He conducted most of his research at the University of Wisconsin–Madison, where
humanistic psychologist Abraham Maslow worked for a time with him. Harlow's
experiments were controversial; they included rearing infant monkeys in
isolation chambers for up to 24 months, from which they emerged severely
disturbed. Some researchers cite the experiments as a factor in the rise of the
animal liberation movement in the United States.
Harlow received numerous awards and honors, including the Howard Crosby Warren Medal (1956), the National Medal of Science (1967), and the Gold Medal from the American Psychological Foundation (1973). He served as head of the Human Resources Research branch of the Department of the Army from 1950–1952, head of the Division of Anthropology and Psychology of the National Research Council from 1952–1955, consultant to the Army Scientific Advisory Panel, and president of the American Psychological Association from 1958-1959.
Dr. Harry Harlow came to the University of Wisconsin-Madison in 1930 after obtaining his doctorate under the guidance of several distinguished researchers, including Calvin Stone and Lewis Terman, at Stanford University. Dr. Harlow began his career with nonhuman primate research working with the primates at the Henry Vilas Zoo, where he developed the Wisconsin General Testing Apparatus (WGTA) to study learning, cognition, and memory. It was through these studies that Harlow discovered that the monkeys he worked with were developing strategies for his tests. What would later become known as learning sets, Harlow described as “learning to learn”.
In order to study the development of these learning sets, Harlow needed access
to developing primates, so he established a breeding colony of Rhesus macaques
in 1932. Due to the nature of his study, Harlow needed regular access to infant
primates and thus chose to rear them in a nursery setting, rather than with
their protective mothers. This alternative rearing technique, also called maternal deprivation, is highly controversial to this day, and is used, in variants, as a model of early life adversity in primates.
Research with and caring for infant rhesus monkeys further inspired Harlow, and
ultimately led to some of his best known experiments: the surrogate mothers.
Although Harlow, his students, contemporaries, and associates soon learned how
to care for the physical needs of their infant monkeys, the nursery-reared
infants remained very different from their mother-reared peers. Psychologically
speaking, these infants were slightly strange: they were reclusive and had
definite social deficits, and they clung to their cloth diapers. For instance, babies that had grown up with only a mother and no playmates showed signs of fear or aggressiveness.
Noticing their attachment to the soft cloth of their diapers and the
psychological changes that correlated with the absence of a maternal figure,
Harlow sought to investigate the mother-infant bond. This relationship was under fire in the early twentieth century as B.F. Skinner and the Behaviorists took on John Bowlby in the discussion of the mother’s importance in the development of the child, the nature of their relationship, and the impact of physical contact between parent and child.
The studies were motivated by John Bowlby's World Health Organization-sponsored study and report, "Maternal Care and Mental Health" in 1950, in which Bowlby
reviewed previous studies on the effects of institutionalization on child
development such as René Spitz's and his own surveys on children raised in a variety of settings. In 1953, his colleague, James Robertson, produced a short and controversial documentary film titled A Two-Year-Old Goes to Hospital demonstrating the almost immediate effects of maternal separation. Bowlby's report, coupled with Robertson's film, demonstrated the importance of the primary caregiver in human and non-human primate development. Bowlby de-emphasized the mother's role in feeding as a basis for the development of a strong mother-child relationship. However, his conclusions generated much debate. It was the debate concerning the reasons behind the demonstrated need for maternal care that Harlow addressed in his studies with surrogates. Physical contact with infants was considered harmful to their development and this view led to sterile, contactless nurseries across the country. Bowlby disagreed, saying that the mother provides much more than food to the infant, including a unique bond that positively influences the child’s development and mental health.
To investigate the debate, Dr. Harlow created inanimate surrogate mothers for
the rhesus infants from wire and wood. Each infant became attached to its particular mother, recognizing its unique face and preferring it above all 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 cloth 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, and in the other, the cloth mother held the bottle and the wire mother had nothing.
Overwhelmingly, the infant macaques preferred spending their time clinging to
the cloth mother. Even when only the wire mother could provide nourishment, the monkeys visited her only to feed. Harlow concluded that there was much more to the mother/infant relationship than milk and that this “contact comfort” was essential to the psychological development and health of infant monkeys and children. It was this research that gave strong, empirical support to Bowlby’s assertions on the importance of love and mother/child interaction.
Successive experiments concluded that infants used the surrogate as a base for exploration and a source of comfort and protection in novel and even frightening situations. In an experiment called the “open-field test,” an infant was placed in a novel environment with novel objects. When the infant’s surrogate mother was present, it clung to her, but then began venturing off to explore. If frightened, the infant would run back to the surrogate and cling to her for a time before sallying forth again. Without the surrogate mother’s presence, the monkeys were paralyzed with fear, huddling in a ball and sucking their thumbs.
In the “fear test,” infants were presented with a fearful stimulus, often a
noisemaking teddy bear. Without the mother, the infants cowered and avoided the object. When the surrogate mother was present, however, the infant did not show great fearful responses and often contacted the device—exploring and attacking it.
Another study looked at the differentiated effects of being raised with only
either a wire mother or a cloth mother. Both groups gained weight at equal rates, but the monkeys raised on a wire mother had softer stool and trouble digesting the milk, frequently suffering from diarrhea. Harlow's interpretation of this behavior, which is still widely accepted, was that a lack of contact comfort is psychologically stressful to the monkeys and the digestive problems are a physiological manifestation of that stress.
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.
Some of Dr. Harlow’s final experiments explored social deprivation in the quest to create an animal model for the study of depression. This study is the most controversial and involved isolation of infant and juvenile macaques for various periods of time. Monkeys placed in isolation exhibited social deficits when introduced or re-introduced into a peer group. They appeared unsure of how to interact with their conspecifics and mostly stayed separate from the group, demonstrating the importance of social interaction and stimuli in forming the ability to interact with conspecifics in developing monkeys, and, comparatively, in children.
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.
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. For the study, some of the monkeys were kept in solitary isolation 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 raised 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.
Since Harlow's pioneering work in touch research in development, recent work in rats have found evidence that touch during infancy have resulted in a decrease in corticosteroid, a steroid hormone involved in stress, and an increase in glucocorticoid
receptors in many regions of the brain. Schanberg and Field found that even short-term interruption of mother-pup interaction in rats markedly affected several biochemical processes in the developing pup: a reduction in ornithine decarboxylase (ODC) activity, a sensitive index of cell growth and differentiation; a reduction in growth hormone release (in all body organs, including the heart and liver and throughout the brain, including the cerebrum, cerebellum and brain stem); an increase in corticosterone secretion; and suppressed tissue ODC responsivity
to administered growth hormone. Additionally, it has been found that these animals who were touch deprived had weakened immune systems. Investigators have measured a direct, positive relationship between the amount of contact and grooming an infant monkey receives during its first six months of life and its ability to produce antibody titer (IgG and IgM)
in response to an antibody challenge (tetanus) at a little over one year of age. Trying to identify a mechanism for the "immunology of touch," some investigators point to modulations of arousal and associated CNS-hormonal activity. Touch deprivation may cause stress-induced activation of the pituitary-adrenal system, which, in turn, leads to increased plasma cortisol and adrenocorticotropic hormone. Likewise, researchers suggest, regular and "natural" stimulation of the skin may moderate these pituitary-adrenal responses in a positive and healthful way.
The pit of despair was a name used by American comparative psychologist Harry Harlow for a device he designed, technically called a vertical chamber apparatus, that he used in experiments on rhesus macaque monkeys at the University of Wisconsin–Madison in the 1970s. The aim of the research was to produce an animal model of clinical depression. Researcher Stephen Suomi described the device as "little more than a stainless-steel trough with sides that sloped to a rounded bottom":
A 3/8 in. wire mesh floor 1 in. above the bottom of the chamber allowed waste material to drop through the drain and out of holes drilled in the stainless-steel. The chamber was equipped with a food box and a water-bottle holder, and was covered with a pyramid top [removed in the accompanying photograph], designed to discourage incarcerated subjects from hanging from the upper part of the chamber.
Harlow had already placed newly born monkeys in isolation chambers for up to one year. With the pit of despair, he placed monkeys between three months and three years old in the chamber alone, after they had bonded with their mothers, for up to ten weeks. Within a few days, they had stopped moving about and remained huddled in a corner.
Much of Harlow's scientific career was spent studying maternal bonding, what he described as the "nature of love". These experiments involved rearing newborn monkeys with surrogate mothers, ranging from toweling covered cones to a machine that modeled abusive mothers by assaulting the baby monkeys with cold air or spikes. The point of the experiments was to pinpoint the basis of the mother-child relationship, namely whether the infant primarily sought food or affection. Harlow concluded it was the latter.
In 1971, Harlow's wife died of cancer and he began to suffer from depression. He was treated and returned to work but, as Lauren Slater writes, his colleagues noticed a difference in his demeanor. He abandoned his research into maternal attachment and developed an interest in isolation and depression.
Harlow's first experiments involved isolating a monkey in a cage surrounded by steel walls with a small one-way mirror, so the experimenters could look in, but the monkey could not look out. The only connection the monkey had with the world was when the experimenters' hands changed his bedding or delivered fresh water and food. Baby monkeys were placed in these boxes soon after birth; four were left for 30 days, four for six months, and four for a year.
After 30 days, the "total isolates," as they were called, were found to be "enormously disturbed." After being isolated for a year, they barely moved, did not explore or play, and were incapable of having sexual relations. When placed with other monkeys for a daily play session, they were badly bullied. Two of them refused to eat and starved themselves to death.
Harlow also wanted to test how isolation would affect parenting skills, but the isolates were unable to mate. Artificial insemination had not then been developed; instead, Harlow devised what he called a "rape rack," to which the female isolates were tied in normal monkey mating posture. He found that, just as they were incapable of having sexual relations, they were also unable to parent their offspring, either abusing or neglecting them. "Not even in our most devious dreams could we have designed a surrogate as evil as these real monkey mothers were," he wrote. Having no social experience themselves, they were incapable of appropriate social interaction. One mother held her baby's face to the floor and chewed off his feet and fingers. Another crushed her baby's head. Most of them simply ignored their offspring.
These experiments showed Harlow what total and partial isolation did to developing monkeys, but he felt he had not captured the essence of depression, which he believed was characterized by feelings of loneliness, helplessness, and a sense of being trapped, or being "sunk in a well of despair," he said.
The technical name for the new depression chamber was "vertical chamber apparatus," though Harlow himself insisted on calling it the "pit of despair." He had at first wanted to call it the "dungeon of despair," and also used terms like "well of despair," and "well of loneliness." Blum writes that his colleagues tried to persuade him not to use such descriptive terms, that a less visual name would be easier, politically speaking. Gene Sackett of the University of Washington in Seattle, one of Harlow's doctoral students who went on to conduct additional deprivation studies, said, "He first wanted to call it a dungeon of despair. Can you imagine the reaction to that?"
Most of the monkeys placed inside it were at least three months old and had already bonded with others. The point of the experiment was to break those bonds in order to create the symptoms of depression. The chamber was a small, metal, inverted pyramid, with slippery sides, slanting down to a point. The monkey was placed in the point. The opening was covered with mesh. The monkeys would spend the first day or two trying to climb up the slippery sides. After a few days, they gave up. Harlow wrote, "most subjects typically assume a hunched position in a corner of the bottom of the apparatus. One might presume at this point that they find their situation to be hopeless." Stephen J. Suomi, another of Harlow's doctoral students, placed some monkeys in the chamber in 1970 for his PhD. He wrote that he could find no monkey who had any defense against it. Even the happiest monkeys came out damaged. He concluded that even a happy, normal childhood was no defense against depression.
The experiments delivered what science writer Deborah Blum has called "common sense results," namely, that monkeys, normally very social animals in nature, emerge from isolation badly damaged, and that some recover while others do not.