This period solidified attachment theory as a central framework for socioemotional development, linking early caregiver responsiveness to later emotion regulation, social competence, and resilience. Researchers increasingly recognized that secure attachments provide a stable base for exploration and learning, shaping internal representations that guide lifelong relationships. Concurrently, nonshared environmental effects within families highlighted that individual trajectories emerge from unique experiences and interactions, not solely parental inputs. Methodologically, longitudinal and observational approaches became standard, enabling tracing of early bonds to preschool social cognition, emotion comprehension, and peer relations.