In 1967 and 1968, Mary Ainsworth, a psychoanalyst who worked with John Bowlby, set up the Strange Situation experiment with a view to analysing how children respond when they are in an unfamiliar surrounding both with their mother and with an unfamiliar person – a stranger. She had started to embrace Bowlby's notion that there was a separate set of biological behaviours that formed the mother-infant attachment and therefore she wanted to match his theoretical views with practical application. The experiment to a certain degree mirrored what Harlow had done with the rhesus monkeys. Ainsworth chose an unfamiliar room in which to carry out this experiment as she believed that the balance between attachment and exploratory behaviour could more easily be observed in an unfamiliar environment. Over one hundred one-year-old middle-class white children from Baltimore were used in four different samples.
The room used in the experiment was set up like a playroom, with novel colourful, noisy and soft toys as illustrated in Figure 1: The Strange Situation Room Layout. There were three chairs, strategically positioned – a baby chair heaped with toys, a chair for the child's mother positioned diagonally across from it and directly across from this chair was another one, for the stranger. Essentially, Ainsworth wanted to test Bowlby's secure base hypothesis – that the children will explore their environment when they feel they can trust their carer. In the experiment, a sequence of events took place. Firstly, while the mother was still present, a stranger entered the room and approached the child. This was testing Bowlby's safe haven hypothesis that a child would return to its mother when any threat or perceived threat was obvious. Secondly, the mother left the room and the stranger remained. This was testing the separation distress hypothesis whereby the child would be distressed when the mother would leave the room. Thirdly, the mother returned and the stranger slipped out. This was to test Ainsworth's own hypothesis with regard to how the child responds to the mother upon reunion, which later evolved into the secure and insecure models of attachment. Fourthly, the baby was left on its own in the room again testing separation distress.
The importance of the Strange Situation experiment cannot be understated. It was the first statistical evidence to validate Bowlby’s theoretical views. The experiment has been repeated many times since in many different cultures and countries with impressively similar results (Hesse, 1999).
The video below shows a strange situation experiment from beginning to end. The infant in question shows securely attached behaviour. Posting this on the web raises interesting ethical questions as obviously, the infant's permission was not obtained.