The sensorimotor stage, the initial phase of Jean Piaget's theory of cognitive development, spans the first two years of a child's life. During this period, infants actively engage with their surroundings, building cognitive awareness through direct interaction with the world. This interaction is primarily based on sensory perception and motor actions, allowing infants to gradually understand basic physical properties and predict how objects interact within their environment.

Exploration Through Sensory-Motor Coordination

Infants primarily explore objects using their senses, often mouthing them to discern their texture and edibility. As their motor skills develop, particularly their ability to grasp, infants experiment with objects by shaking, banging, or dropping them to observe cause-and-effect relationships, such as the sound produced when an object strikes a surface. This stage is characterized by gradually improving the ability to combine sensory input with motor responses, enhancing the infant's capacity to interact with their environment purposefully.

Development of Object Permanence

Piaget theorized that, early in the sensorimotor stage, infants lack object permanence — the understanding that objects continue to exist even when they are no longer visible. Infants under five months generally assume that an object ceases to exist once it is out of sight. However, between five and eight months, they begin developing object permanence, considered a major cognitive milestone in infancy. Piaget investigated object permanence by presenting an infant with a toy and then hiding it under a blanket. He believed that if the infant grasped that the toy was still there, they would attempt to uncover it. Infants search for hidden objects, reflecting their emerging ability to mentally represent objects and recognize their continued existence beyond immediate visibility.

Stranger Anxiety and Schema Formation

Around the same time as object permanence develops, infants begin to exhibit stranger anxiety, a natural response of fear or discomfort when confronted with unfamiliar individuals. According to Piaget, this response arises because infants cannot yet assimilate the image of an unfamiliar person into an established mental schema, causing distress and prompting defensive reactions such as crying, clinging to caregivers, or averting their gaze. Stranger anxiety signifies the infant's growing cognitive differentiation between familiar and unfamiliar stimuli, a crucial aspect of early social development within the sensorimotor stage.