In psychology, anomalistic psychology is the study of human behaviour and experience connected with what is often called the paranormal, with few assumptions made about the validity (or otherwise) of the reported phenomena.
According to anomalistic psychology, paranormal phenomena have naturalistic explanations resulting from psychological and physical factors which have given the false impression of paranormal activity to some people. There were many early publications that gave rational explanations for alleged paranormal experiences.
The physician John Ferriar wrote An Essay Towards a Theory of Apparitions in 1813 in which he argued that sightings of ghosts were the result of optical illusions. Later, the French physician Alexandre Jacques François Brière de Boismont published On Hallucinations: Or, the Rational History of Apparitions, Dreams, Ecstasy, Magnetism, and Somnambulism in 1845 in which he claimed sightings of ghosts were the result of hallucinations. William Benjamin Carpenter, in his book Mesmerism, Spiritualism, Etc: Historically and Scientifically Considered (1877), wrote that Spiritualist practices could be explained by fraud, delusion, hypnotism and suggestion. The British psychiatrist Henry Maudsley, in Natural Causes and Supernatural Seemings (1886), wrote that so-called supernatural experiences could be explained in terms of disorders of the mind and were simply "malobservations and misinterpretations of nature".
In the 1890s, the German psychologist Max Dessoir and psychiatrist Albert Moll formed the "critical occultism" position. This viewpoint interpreted psychical phenomena naturalistically. All apparent cases were attributed to fraud, suggestion, unconscious cues or psychological factors. Moll wrote that practices such as Christian Science, Spiritualism and occultism were the result of fraud and hypnotic suggestion. Moll argued that suggestion explained the cures of Christian Science, as well as the apparently supernatural rapport between magnetisers and their somnambulists.