The vertical chamber was 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 placed baby monkeys in the chamber alone for up to one year. Within a few days, they stopped moving about and remained huddled in a corner. The monkeys were found to be psychotic when removed from the chamber, and most did not recover.
Harlow's first experiments into the effects of loneliness 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 couldn't 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, didn't explore or play, and were incapable of having sexual relations. When put with other monkeys for a daily play session, they were badly bullied. Two of them refused to eat and starved themselves to death.
In order to find out how the isolates would parent, Harlow devised what he called a "rape rack," to which the female isolates were tied in the position taken by a normal female monkey in order to be impregnated. Artificial insemination had not been developed at that time. 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 hadn't 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.
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.
According to Harlow: "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."
Steven Suomi, one of Harlow's many doctoral students, placed some monkeys in the chamber 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": that monkeys, very social animals in nature, when placed in isolation, emerge badly damaged, and that some recover and some do not.
Gene Sackett of the University of Washington in Seattle, and another of Harlow's doctoral students who went on to conduct additional deprivation studies, told Blum that, in his view, the animal liberation movement in the U.S. was born as a result of Harlow's experiments. Willam Mason, another of Harlow's students who continued after leaving Wisconsin, told Blum that Harlow "kept this going to the point where it was clear to many people that the work was really violating ordinary sensibilities, that anybody with respect for life or people would find this offensive. It's as if he sat down and said, 'I'm only going to be around another ten years. What I'd like to do, then, is leave a great big mess behind.' If that was his aim, he did a perfect job."