What does a baby do when its parent leaves the room?

Mary Ainsworth's Strange Situation is a short, slightly nerve-wracking play session. A child plays with toys while a parent and a stranger enter and leave the room, and observers record how the child behaves. The pattern of behavior is read as a style of attachment.

John Bowlby's attachment theory says infants need a close relationship with at least one primary caregiver to survive and develop healthy social and emotional functioning. Ainsworth had carried out a field study of mother-infant interaction in Africa in 1954, and in 1965 she designed the procedure to assess individual differences in how babies behave under stress.

She described three patterns, and a fourth was added later. A securely attached child explores freely with the caregiver present, using them as a secure base, may be visibly upset when the caregiver leaves, and is happy to see them back. An anxious-avoidant child ignores the caregiver and shows little emotion when they leave or return, though Ainsworth and Bell theorised that this calm is a mask for distress, later supported by heart-rate studies. An anxious-ambivalent child is distressed even before separation and clingy and hard to comfort on return. Main and Solomon added a fourth, disorganized, style in 1990.

Researchers do not read the results the same way. Attachment researchers say a child becomes securely attached when the caregiver is responsive, while others point to other determinants and note the child's behavior may influence the parent's. Critics also note that the procedure may not mean the same thing in cultures where infants are rarely separated from their mothers.