Answer the following Q with stream of consciousness. Context: In his theory of Cognitive development, Jean Piaget proposed that humans progress through four developmental stages: the sensorimotor, preoperational, concrete operational and formal operational period. The first of these, the sensorimotor stage "extends from birth to the acquisition of language." In this stage, infants progressively construct knowledge and understanding of the world by coordinating experiences (such as vision and hearing) with physical interactions with objects (such as grasping, sucking, and stepping). Infants gain knowledge of the world from the physical actions they perform within it. They progress from reflexive, instinctual action at birth to the beginning of symbolic thought toward the end of the stage.

Question: according to jean piaget what is the stage of cognitive development at infancy?
To answer the question, consider the following: The first of these, the sensorimotor stage "extends from birth to the acquisition of language." Therefore, the final answer is the sensorimotor stage.