The Strange Situation Procedure

During the 1960's Mary Ainsworth and colleagues developed the Strange Situation Procedure (SSP) as a method of assessing the nature of an infant's attachment to a caregiver at 12 and 18 months of age (Ainsworth & Bell, 1970; Ainsworth, Bell & Stayton, 1971; Ainsworth, Blehar, Waters & Wall, 1978).

The strange situation procedure involves a neutral room that is kitted out with toys and two chairs (similar to a GP's waiting room). The room is also fitted with video surveillance to allow recording of behaviours during the procedure. Apart from the caregiver and infant, an individual who is a stranger to the infant (a confederate of the researchers) is required. Eight episodes ensue:

1. The observer introduces mother and baby to the room then leaves and begins recording from the adjacent video surveillance room (about half a minute).
2. The mother sits and leaves the baby to explore (2 minutes).  If necessary, the mother encourages the infant to engage in play with the supplied toys on the floor (1 minute).
3. The stranger enters the room and is silent (1 minute), converses with the mother (1 minute), then approaches the baby and attempts to initiate play (1 minute).
4. The mother unobtrusively leaves the room as the stranger initiates play with the baby. She remains out of the room for up to 3 minutes (shorter if the baby becomes distressed).
5. The stranger leaves unobtrusively and the mother returns to greet and comfort the baby (3 minutes or more if required). Once the baby is calmed, the mother returns it to the floor and encourages it to play with the toys available.
6. The mother leaves, saying "bye-bye" to the baby. The baby is left alone briefly (3 minutes or less if the baby shows distress).
7. The stranger enters the room and attempts to comfort/engage with the baby (3 minutes or less if baby shows distress).
8. The stranger leaves unobtrusively as the mother enters the room and greets/comforts the baby (3 minutes or more if required).

Note that the above procedure includes the following events of particular interest:

• Separation from caregiver (episodes 4 and 6)
• Reunion with caregiver (episodes 5 and 8)
• Stranger anxiety (episodes 3, 4 and 7)

Attachment style classification is made into one of three categories (A, B or C below) based on coded behaviours of the infant during these events. Expected caregiver behaviour (but not necessarily during the procedure) is also listed.