Object Permanence in Infants: Baillargeon's Drawbridge Experiment and What Piaget Missed

Piaget judged object permanence by whether a baby searched for a hidden toy — but young infants simply cannot yet reach and remove a cover. Baillargeon used the violation-of-expectation method: babies look longer at events that surprise them.
Infants first watched a screen rotate through 180°, like a drawbridge, until they lost interest (habituation). A box was then placed behind it. In the "possible" event, the screen stopped when it reached the box. In the "impossible" event, the box was secretly removed and the screen rotated the full 180° — as if through a solid object.

The study challenged Piaget's timetable and helped launch the core knowledge approach: infants hold basic expectations about the physical world very early. It also carries a methodological lesson — failing to act is not failing to understand. Some researchers later proposed simpler perceptual explanations, and the debate over how to interpret looking times continues.

Your baby understands far more than they can show with their hands. Peekaboo and hiding toys under a cloth are not just fun — they exercise a developing mind.

Early assessment should distinguish knowledge from its expression in action. Looking-time methods let us study cognition before speech and mature motor skills — including in children with motor impairments.