Developmental psychologists are those doctors who study the changes that occur in human development over the course of the lifespan. Developmental psychologists practice a specialized subset of the field of psychology, one that traditionally looked at development in childhood, but has expanded in recent years to include adulthood as well, as developmental psychologists have come to the understanding that mental growth and change do not stop in the development of adolescence.
One of the first scientists to propose a theory of development was Sigmund Freud, who developed his famous psychosexual development theory. Freud maintained that there were five stages of universal development: the oral, anal, phallic, latent, and genital stages. Freud's stages of development ended at adulthood. Erik Erikson reinterpreted Freud's stages to create a system of psychosocial development, which characterized change across the entire human lifespan, spurred by identity crisis.
Developmental psychologists research in several major areas, including cognitive, social, emotional, and physical development. Because infants and children cannot participate in research tests the same ways that adults can, developmental psychologists often must modify research methods, relying heavily on systematic observation, interviews and case studies. These methods have provided an ever-changing view of the changing nature of human growth and development.