One of the first psychologists to extensively explore the concept of impression formation was Solomon Asch. His research, dating back to the mid-1940s, provided a substantial amount of the initial data explaining factors that affect impression formation. He was particularly interested in the differences between central and peripheral traits. Many of the ideas produced from Asch's experiments are still relevant to the study of impression formation, and have played a significant role in establishing a foundation for modern implicit personality theory research.