Kurt Lewin was a German-American psychologist, known as one of the modern pioneers of social, organizational, and applied psychology in the United States. During his professional career Lewin applied himself to three general topics: applied research, action research, and group communication.

Max Wertheimer was a psychologist who was one of the three founders of Gestalt psychology, along with Kurt Koffka and Wolfgang Köhler. He is known for his book, Productive Thinking, and for conceiving the phi phenomenon as part of his work in Gestalt psychology.