Sensorimotor Stage

The sensorimotor stage is the first of the four stages of cognitive development proposed by the Swiss psychologist Jean Piaget, spanning roughly from birth to about two years of age, during which an infant comes to understand the world almost entirely through direct sensory experience and physical, motor action rather than through internal mental symbols or language. Piaget divided the stage into six progressive substages, beginning with simple reflexive responses to stimulation in the first month of life, moving through increasingly deliberate and repeated actions the infant performs first on their own body and then on external objects to reproduce interesting effects, and culminating in the beginnings of mental representation, in which the infant becomes capable of briefly imagining an object or action internally before physically carrying it out, a capacity Piaget called the invention of new means through mental combination. The most significant achievement Piaget associated with this stage is the emergence of object permanence, the understanding that an object continues to exist even when it can no longer be seen, heard, or touched, which Piaget believed developed only gradually and was not fully secure until near the stage's end, though later researchers using less demanding testing methods, most notably Renee Baillargeon's violation-of-expectation studies, found evidence that infants hold at least an implicit understanding of object permanence considerably earlier than Piaget's own original testing procedures were able to detect. The sensorimotor stage also lays the groundwork for early language development and symbolic play, both of which become far more prominent in the preoperational stage that follows it.