The development of human beings’ cognitive, emotional, intellectual, and social capabilities and functioning over the course of the life span, from infancy through old age.
Infancy is the period between birth and the acquisition of language one to two years later. Young infants are capable of complex perceptual judgments involving distance, shape, direction, and depth, and they are soon able to organize their experience by creating categories for objects and events (e.g., people, furniture, food, animals) in the same way older people do. Infants make rapid advances in both recognition and recall memory, and this in turn increases their ability to understand and anticipate events in their environment. A fundamental advance at this time is the recognition of object permanence-i.e., the awareness that external objects exist independently of the infant’s perception of them. At about 18 months of age, the child starts trying to solve physical problems by mentally imagining certain events and outcomes rather than through simple trial-and-error experimentation. Infants already display behavioral reactions suggestive of such emotional states as surprise, distress, relaxation, and excitement. New emotional states, including anger, sadness, and fear, all appear by the first year. Infants’ emotional life is centered on the attachments they form toward the mother or other primary caregiver, and through these mutual interactions infants learn to love, trust, and depend on other human beings. Babies begin to smile at other people beginning about two months, and by six months they have developed an attachment to their mother or other caregiver. These attachments form the basis for healthy emotional and social development throughout childhood.
The early years of childhood are marked by enormous strides in the understanding and use of language. Children begin to comprehend words some months before they themselves actually speak. The average infant speaks their first words by 12-14 months, and by the 18th month, they have a speaking vocabulary of about 50 words. The child begins to use two- and then three-word combinations and progresses from simple noun-verb combinations to more grammatically complex sequences, using conjunctions, prepositions, articles, and tenses with growing fluency and accuracy. By the fourth year most children can speak in adult-like sentences and have begun to master the more complex rules of grammar and meaning.
In their cognitive abilities, children make a transition from relying solely on concrete, tangible reality to performing logical operations on abstract and symbolic material. Even a two-year-old child behaves as though the external world is a permanent place, independent of their perceptions; and they exhibit experimental or goal-directed behavior that may be creatively and spontaneously adapted for new purposes. During the period from two to seven years, the child begins to manipulate the environment by means of symbolic thought and language; they become capable of solving new types of logical problems and begin to use mental operations that are flexible and fully reversible in thought.
Emotionally, children develop in the direction of greater self-awareness-i.e., awareness of their own emotional states, characteristics, and potential for action-and they become increasingly able to discern and interpret the emotions of other people as well. This contributes to empathy, or the ability to appreciate the feelings and perceptions of others and understand their point of view. These new abilities contribute to the child’s moral development, which typically begins in early childhood as concern over and avoidance of acts that attract pain and punishment and progresses to a more general regulation of conduct so as to maintain parental regard and approval. All of these emotional advances enhance the child’s social skills and functioning.
