Developmental psychology is the discipline which studies cognitive, emotional, mental and social development. This branch of psychology is particularly interested in how people grow and develop over time. Unlike child psychology, developmental psychology covers age-related changes throughout the human life.
The major dichotomies in developmental psychology are the debates about continuity versus discontinuity and nature versus nurture. Supporters of the continuous model argue that development is a smooth change, while their opponents claim that there are discrete stages in life. On the other hand, the nature-versus-nurture debate is centered on the role of heredity and genetics as opposed to learning and upbringing.
Developmental psychology rests on the definition of the term development, which in particular focuses on social, cognitive and emotional changes in one's life. This discipline identifies the biological, psychological and social aspects that interact to influence the process of growing.
One of the major theories in developmental psychology is the psychoanalytic model, developed by Austrian psychologist Sigmund Freud (1856–1939). Freud laid a strong emphasis on the child's experiences, saying that early traumas play a crucial role in one's adult experiences. Freud's theory has been criticized for being too focused on the early years and too deterministic.
According to Freud's psychosexual model, the human life is divided into five stages: oral, anal, phallic, latency and genital. The oral phase lasts from one's birth to the age of 18 months, when the primary source of pleasure for the newborn is sucking. The anal stage continues from 18 months to 3.5 years, when sexual pleasure is centered upon the anus, according to Freud, and the child develops self-control and obedience. During the phallic stage – from 3.5 years to 6 years – children are particularly interested in playing with their genitals. This stage is marked by the development of morality and sexual identification. The latency period continues from the age of 6 to the adolescent years, when the sexual and aggressive drives are less active. Finally, the genital stage is focused on the genitals and is marked by maturity, reproduction as well as intellectual and artistic creativity.
Another key figure in developmental psychology is Swiss-born psychologist Jean Piaget (1896-1980), who conducted research into cognitive development. As a founder of genetic epistemology, he expressed the view that children were not just passive recipients of information, but scientists who actively constructed knowledge and understanding of the world: "During the earliest stages the child perceives things like a solipsist who is unaware of himself as subject and is familiar only with his own actions." According to Piaget's psychological model, cognitive development goes through the stage of assimilation, or the integration of new information into previously existing schema; as well as accommodation, or the process of change and alteration of existing schema following the acquisition of new information.
Other developmentalists study physical, motor, intellectual, emotional, social and moral changes throughout all stages of life. For instance, the holistic biopsychological model focuses on the interrelationship between biological, psychological and social factors in development. This theory explains psychological phenomena through multiple causes.
Furthermore, the focus in developmental psychological research has shifted from early childhood towards adult life, because of the growing awareness of adult stages of the life span. Hence, developmental psychology has gone through a paradigm shift as a result of the increased interest in middle and later adulthood and the understanding that developmental changes occur throughout a person's life (Eckberg and Hill, 1979). The impact of gerontology on developmental psychology has also increased. New research challenges many of the tenets of early developmentalists, in particular Freud and Piaget.
Research in developmental psychology can take various forms. Under the cross-sectional method mixed-age groups are studied for similar traits. In longitudinal research, studies focus on a person's change over time. The cross-sequential method is a combination of the cross-sectional and the longitudinal models.