During the sensorimotor stage of human development, children understand the world through their senses, so they put all types of objects in their mouths, shake rattles repeatedly to make sounds and press buttons to turn lights on and off. They use only their sensory perceptions and motor activities to explore and understand the world.
The sensorimotor stage lasts from birth to 24 months. At first, infants can use only their reflexes to interact with their environment. For example, they can suck, grasp and look. As their brains develop, infants begin to intentionally repeat actions that provide pleasure, such as sucking a thumb.
At four to eight months, infants intentionally repeat actions that affect their environment, such as reaching to grab a toy. They also react to a person or thing hidden from view as if it does not exist. For example, if a ball a child is playing with is covered by a blanket, the child does not look under the blanket to find the ball. A few weeks later, when he develops object permanence, the child understands that the ball still exists even if he cannot see it.
During the second half of the sensorimotor stage, children begin imitating the actions of other people and experimenting with new sounds and behavior. They also develop stranger anxiety, or a fear of unrecognized people.