Building on Freud's work, Carl Jung concentrated on the concepts of extraversion and introversion, recognizing the dual nature frequently observed in human personalities. This duality, especially in the context of an individual's private and public selves, was seen by many of his followers as a universal trait. Subsequent psychologists, such as Karen Horney and Ernest Jones, who were influenced by these early explorations of the unconscious, often included the now antiquated term "split personality" in their studies of abnormal behavior. Today, "dissociation" is more commonly used, describing "processes [that] function independently of the rest of the personality." While professional analysts might explore this phenomenon in more depth, Stevenson uniquely dramatized it in a way that no one else could match.