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 use of 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, had definite social deficits, and clung to their cloth diapers. At the same time in the reverse configuration, 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 constant scrutiny in the early twentieth century, as B. F. Skinner and the behaviorists took on John Bowlby in a discussion of the mother's importance in the development of the child, the nature of their relationship, and the impact of physical contact between mother 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, and the distress experienced by children when separated from their mothers, 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,