German psychologist who had a special interest in parapsychology —he coined the term during or before 1889. He also had both talent and interest in art and aesthetics. A precocious child, he was an accomplished musician who played the violin for the German emperor. His experiments in muscle reading and thought-transference were undertaken in 1885 at the age of 18 and reported in the Proceedings of the Society for Psychical Research (1885). Three years later he founded the Gesellschaft fur Experimental Psychologie (Society for Experimental Psychology), dedicated to the study of hypnosis and paranormal phenomena.
Dessoir collaborated with Albert Moll on experiments in hypnotic rapport. He originated a theory of "Doppel-Ich" or double ego, suggesting that human consciousness is not a unit merely to our own consciousness, but actually consists of at least two distinguishable personalities, each held together by its own chain of memories. Because of this, an action that is quite intelligible can be performed unconsciously (i.e., without the agent noticing what he or she is doing, or even breaking off a conversation).
As he matured, Dessoir saw himself as an instrument for educating the German public on psychical research. He founded the periodical Zeitschrift für kritischen Okkultismus and wrote Vom Jenseits der Seele (1917). He also investigated several mediums including Eusapia Palladino.