Which type of psychologist focuses on changes in behavior from infancy through old age?

The focus of a developmental psychologist is on the various stages of human development and the changes in behavior that occur from infancy through old age. This branch of psychology examines how individuals grow and evolve physically, emotionally, socially, and cognitively throughout their lifespan. Developmental psychologists study the impact of nature and nurture on behavior and development, as well as the milestones associated with different life stages. This includes understanding the typical patterns of development, factors that may influence individual differences, and the effects of various life experiences on overall development.

In contrast, cognitive psychologists primarily investigate mental processes such as thinking, memory, and problem-solving at any given stage of life rather than emphasizing the changes over a lifespan. Clinical psychologists focus on diagnosing and treating mental health issues, which may apply across various ages but does not specifically center on developmental changes sequentially. Social psychologists study how individuals are influenced by social contexts and interactions rather than the overall trajectory of human development. Therefore, the distinct emphasis of developmental psychologists on changes across the entirety of human life makes this the correct response.