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, but 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, contact-less nurseries across the country. Bowlby disagreed, claiming 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, 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 clothed 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. In the other situation, 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 ran back to the surrogate mother and clung to her for a time before venturing out again. Without the surrogate mother's presence, the monkeys were paralyzed with fear, huddling in a ball and sucking their thumbs. In the "fear