Senses used by mental mediums are sometimes defined differently from in other paranormal fields. A medium is said to have psychic abilities but not all psychics function as mediums. The term clairvoyance, for instance, may include seeing spirit and visions instilled by the spirit world. The Parapsychological Association defines "clairvoyance" as information derived directly from an external physical source.[37] 

The British medium William Roy earned over £50,000 from his séance sitters. He confessed to fraud in 1958 revealing the microphone and trick-apparatus that he had used.[166] The automatic writings of the Irish medium Geraldine Cummins were analyzed by psychical researchers in the 1960s and they revealed that she worked as a cataloguer at the National Library of Ireland and took information from various books that would appear in her automatic writings about ancient history.[167] 

In 1876, William Eglinton was exposed as a fraud when the psychical researcher Thomas Colley seized a "spirit" materialization in his séance and cut off a portion of its cloak. It was discovered that the cut piece matched a cloth found in Eglinton's suitcase.[79] Colley also pulled the beard off the materialization and it was revealed to be a fake, the same as another one found in the suitcase of Eglinton.[80] In 1880 in a séance a spirit named "Yohlande" materialized, a sitter grabbed it and was revealed to be the medium Mme. d'Esperance herself.[81]

The exposures of fraudulent activity led to a rapid decline in ectoplasm and materialization séances.[199] Investigator Joe Nickell has written that modern self-proclaimed mediums like John Edward, Sylvia Browne, Rosemary Altea and James Van Praagh are avoiding the Victorian tradition of dark rooms, spirit handwriting and flying tambourines as these methods risk exposure. They instead use "mental mediumship" tactics like cold reading or gleaning information from sitters before hand (hot reading). Group readings also improve hits by making general statements with conviction, which will fit at least one person in the audience. Shows are carefully edited before airing to show only what appears to be hits and removing anything that does not reflect well on the medium.[200]

Some scientists of the period who investigated spiritualism also became converts. They included chemist Robert Hare, physicist William Crookes (1832–1919) and evolutionary biologist Alfred Russel Wallace (1823–1913).[13][14] Nobel laureate Pierre Curie took a very serious scientific interest in the work of medium Eusapia Palladino.[15] Other prominent adherents included journalist and pacifist William T. Stead (1849–1912)[16] and physician and author Arthur Conan Doyle (1859–1930).[17]