In this Topic, we discuss the development of cognition and perception in the child. In the first section, we discuss perception, the ability to acquire information about the world. The child's ability to distinguish different visual and auditory stimuli, as well as stimuli in all the rest of the senses, develops rapidly over the course of the first two years. While some of this development is passive, the majority of it depends on the child's active exploration of an environment that provides opportunities for diverse kinds of experiences.

Although the meaning of "perception" is fairly well agreed-upon, "cognition" is a term that has been construed in a variety of ways. In modern psychology it is sometimes used to refer to any "information-processing" approach to the study of behavior. This definition is, however, a bit too broad. A clearer and more specific definition might go as follows: cognition is the structure of our representations of the world and the processes we use to manipulate that structure. The study of cognitive development is thus the study of how both our knowledge of the world and our ways of acquiring new knowledge grow over time. Language is obviously an important part of this growth process--so important, in fact, that it is here covered in a separate Topic. While reading this Topic, keep in mind the role language might play in influencing and enabling other cognitive abilities.

In the second section, we discuss one of the most influential theoretical models of cognitive development. Jean Piaget's model of the stages of cognition, and the observations upon which he founded his model, make him far and away the most important cognitive developmentalist in the history of the field. Piaget distinguished between four stages of development: the sensorimotor stage, the preoperational stage, the concrete-operational stage, and the formal-operational stage. He postulated two processes that drove the child's development: assimilation and accommodation.

In the third section, we discuss some of the criticisms that have been brought against Piaget's model and some of the alternatives that have been offered--specifically, information-processing and social accounts of cognitive development.

Finally, we discuss an area of cognitive development that has become an increasingly popular subject of study over the past twenty years: theory of mind. Theory of mind straddles the divide between cognitive and socioemotional development. It is concerned with the development of a child's recognition of his or her mind and the minds of others, including the child's ability to understand the existence of false beliefs, the use of deception, and the way that beliefs, desires, and actions are related.