Baillargeon

The violation-of-expectation (VOE) paradigm is a method for probing infant cognition without requiring motor responses. Infants are first habituated to a possible, physically consistent event — their looking time declines as it becomes familiar. They are then shown either that event again or a physically impossible version. If infants look significantly longer at the impossible event, researchers infer the infants expected the possible outcome, implying they possess the underlying physical knowledge. Baillargeon used this to bypass the motor limitations of Piaget's reaching tasks, allowing knowledge to be tested far earlier in development.

Baillargeon showed that infants understand object permanence — that objects continue to exist when hidden — far earlier than Piaget's sensorimotor timeline predicts. Baillargeon, Spelke & Wasserman (1985) found evidence at 5.5 months; Baillargeon (1987) replicated at 3.5 months. Piaget had argued object permanence was not established until 8–12 months. Baillargeon argued the discrepancy arises because Piaget's tasks required reaching — a motor skill infants lack at 3–5 months — so his tasks measured performance, not competence.

The drawbridge study (Baillargeon, Spelke & Wasserman, 1985) is the foundational VOE demonstration of early object permanence. Infants were habituated to a drawbridge rotating 112° back and forth. They were then shown either a possible event (the drawbridge stopping when it should encounter a hidden box) or an impossible event (the drawbridge rotating 180° through the hidden box as if it did not exist). Infants looked significantly longer at the impossible event, indicating they expected the box to still exist — evidence for object permanence at 5.5 months, well before Piaget's predicted 8–12 months.