Piaget's stages of cognitive development include the sensorimotor stage from birth to age 2 where infants learn about the world through senses and motor skills. During this stage infants develop object permanence. Piaget's stages have been confirmed but also criticized for underestimating infant competence and not accounting for social influences. Infant intelligence shows individual differences and instability in the first year but can predict later development. Language develops through stages from prelinguistic sounds to telegraphic speech to combining words. Theories propose both innate and learned aspects of language guided by an inborn language acquisition device interacting with the environment during a sensitive period in early childhood.