Mary Ainsworth (1913 - 1999) was a developmental psychologist who became known for her work concerning early emotional attachment of babies to their primary caregivers.
In order to explore Attachment patterns, Ainsworth devised an experimental procedure called "A Strange Situation." The procedure begins with the child and his mother in a room where the child is allowed to play and explore alone. A stranger enters the room, talks to the mother, and approaches the child while the mother leaves the room. After a short period, the mother comes back and reunites with the child. The mother and the stranger leaves, and the child is left to play alone. The stranger then comes back and attempts to interact with the child. The mother returns for a second reunion as the stranger leaves.
Throughout the procedure, the child is observed on four aspects: play behavior, reactions to departure and to the mother's return, and behavior when the stranger is around. Ainsworth categorized the nature of the children's attachment into three groups based on their behaviors.
A child is said to have a Secure Attachment when he is able to freely explore when the mother is around, interacts with the stranger when the mother is present but not when she is absent, shows distress when the mother leaves, and is happy to see the mother return.
Children may also exhibit signs of having Insecure Attachment. A child who has an Anxious-Resistant Insecure Attachment is anxious to explore and is wary of the stranger even when the mother is present, is extremely distressed when the mother leaves, but is ambivalent when the mother returns. He will stay close to the mother upon her return, but will show resentment by resisting the mother's attention and pushing her away. A child with an Anxious-Avoidant Insecure Attachment will avoid or ignore the mother and show little emotion when his mother leaves and upon her return. He will avoid his mother when she attempts to approach him, and does not cling to her when picked up. He does not explore much, whether the mother is present or not, and reacts similarly to the stranger as he does to his mother.
Ainsworth believed that the kind of attachment pattern exhibited by the child is reflective of the quality of care that he receives. Children whose caregiver is appropriately responsive and consistently provides for their needs will develop a Secure Attachment, while those whose caregivers are unresponsive or inconsistent will develop an Insecure Attachment.