Which psychological figure studied the effects of hypnotism and its application in treating hysteria?

The figure who studied the effects of hypnotism and its application in treating hysteria is Josef Breuer. Breuer is notably recognized for his work with Anna O., a patient whose case contributed significantly to the development of psychoanalysis. Through his practice, Breuer employed hypnosis as a therapeutic technique, enabling patients to recall repressed memories and emotions, which he believed were central to their hysterical symptoms. This approach laid the groundwork for future psychological theories and treatments, particularly influencing Sigmund Freud.

While each of the other figures listed contributed to the field of psychology and its understanding of mental disorders, Breuer's specific focus on hypnotism in relation to hysteria is what distinguishes his work. Emil Kraepelin was primarily known for his classification of mental disorders and his focus on psychiatric diagnosis rather than hypnotic techniques. Franz Anton Mesmer, known for his work on animal magnetism, predated Breuer and did influence the development of hypnotism but did not apply it specifically to hysteria in the same way as Breuer. Jean-Martin Charcot is another important figure who used hypnosis in treating hysteria but was more focused on its neurological aspects and did not have the same foundational role in the psychoanalytic tradition as Breuer.