A term that has historically had a variety of meanings and connotations, most of which revolve around the notion of a pathological process by means of which anxiety, generated by an intrapsychic conflict, is unconsciously transformed into an illusory or hallucinatory percept. The term conversion was possibly introduced in 1795 by the British physician John Ferriar (17611815), who used it in the context of what he called hysterical conversion. In 1895, the term conversion was borrowed by the Austrian psychoanalysts Josef Breuer (1842-1925) and Sigmund Freud (1856-1939) to denote the development of sensory and motor symptoms in hysteria. In the literature on sensory conversion, the resulting illusory and hallucinatory percepts are designated as *conversive hallucinations or * conversion hallucinations. In classifications such as the Diagnostic and Statistical Manual ofMental Disorders (DSM), sensory conversion is classified as a symptom of conversion disorder, which itself constitutes a subclass of the somatoform disorders. Conversion disorder is a nosological category which shows considerable overlap with notions such as somatization and hysteria. It is conceptualized as a syndrome characterized by an alteration of sensory and/or motor functions suggestive of a neurological disorder, but one which cannot be confirmed by means of state-of-the-art physical and auxiliary examination. To avoid the pitfall of dealing with a somatic disease as yet unknown to medicine by passing it off as conversion, psychological factors must be presented which are associated with the onset and/or exacerbation of the symptoms. Two common examples of conversion disorder are conversion paralysis and * conversion blindness. In both cases, the affected individual is thought to resolve an underlying conflict by the unconscious use of symptoms. * Scierneuropsia, a psy-chogenic visual disturbance characterized by a perceived lack of brightness in extracorporeal objects and stimuli, may well fit into this category. The term sensory conversion is used in opposition to the term motor conversion, which is conceptualized as a symptom or condition in which anxiety generated by an intrapsychic conflict is transformed into motor symptoms. The 1982 Manual for the Assessment and Documentation of Psychopathology (AMDP) lists pseudoneuro-logic bodily disturbances such as aphonia, blindness, deafness, paresis, abasia, and psychogenic seizures as typical conversion symptoms.
References
Breuer, J., Freud, S. (1956). Studies on hysteria. Translated and edited by Strachey, J., Strachey, A. London: The Hogarth Press and the Institute of Psycho-analysis.
Guy, W., Ban, T.A., eds. (1982). The AMDP-system: Manual for the assessment and documentation of psychopathology. Berlin: Springer.
Sirota, P., Spivac, B., Meshulam, B. (1987). Con-versive hallucinations. British Journal of Psychiatry, 151, 844-846.
Taylor, G.J. (2003). Somatization and conversion: Distinct or overlapping constructs? Journal of the American Academy of Psychoanalysis and Dynamic Psychiatry, 31, 487-508.
Dictionary of Hallucinations. J.D. Blom. 2010.