AP® Psychology · Unit 3 · Topic 3.4
The Sensorimotor Stage and Object Permanence
The sensorimotor stage is Piaget's first stage of cognitive development, from birth to about age two, where infants learn through senses and motor actions and gradually build object permanence, the understanding that things still exist even when hidden from view.
Piaget argued that infants don't start out thinking in words or images. They think with their bodies. Grabbing, mouthing, shaking, and dropping things are how a baby tests what the world is made of: does it rattle, does it taste bitter, does it fall. Each action feeds back information, and the infant slowly builds mental schemas for objects and their properties. This is why the stage is called sensorimotor: sensation and motion are the thinking.
Object permanence grows out of that same hands-on exploration. A very young infant, around four to six months, treats a hidden object as genuinely gone, because their understanding of objects depends on currently sensing them. Somewhere around eight to twelve months, infants start reaching for or searching under a cloth that covers a toy, showing they now mentally represent the object as existing independent of their perception of it. This is a real cognitive milestone, not just a motor skill catching up, because it requires holding an idea in mind without sensory support.
This is also why peekaboo works on babies and not on you. The delight isn't about anticipating a joke, the way an older child enjoys a silly disguise. For an infant whose object permanence is still forming, a face that disappears and then dramatically reappears is a genuinely surprising event each time. Object permanence connects forward to Piaget's later stages, where mental representation expands into symbolic thought, pretend play, and eventually logical reasoning, making this stage the foundation the rest of cognitive development builds on.
Key terms
- Sensorimotor stage
- Piaget's first stage of cognitive development, from birth to roughly age two, where infants learn through senses and motor actions.
- Object permanence
- The understanding that objects continue to exist even when they can no longer be seen, heard, or touched.
- Schema
- A mental structure or framework that organizes knowledge and guides how new information or experience is understood.
- A-not-B error
- A mistake where an infant searches for a hidden object in its previous location even after watching it moved to a new one.
Watch it explained
- How it worksHow does an infant learn the world through grabbing, mouthing, and moving?
- How it worksWalk me through the moment object permanence appears in a hidden-toy test.
- Common mistakeWhy isn't peekaboo funny to a baby for the same reason it is funny to you?
- Going furtherWhat happens in the same test when the object is hidden in a second location?
Check yourself
End of topic.