The study of human psychological changes occurring across the lifespan, arranged in a time-ordered sequence, is fundamental to understanding how individuals think, feel, and behave at different ages. This encompasses cognitive, social, emotional, and physical transformations from infancy to old age. For instance, examining the stages of language acquisition in children or the cognitive decline associated with aging falls under this area of study.
Understanding the typical sequence of psychological changes allows psychologists to identify deviations from expected patterns, potentially indicating developmental delays or disorders. It provides a framework for creating age-appropriate interventions and educational programs. Historically, researchers like Jean Piaget and Erik Erikson contributed significantly by proposing stage-based models that outline the predictable progression of cognitive and psychosocial development, respectively, influencing therapeutic approaches and educational strategies.