- visual allachaesthesia
- Also known as optical allachaesthesia, optical alloaesthesia, and fata morgana of the visual sphere. The first three expressions are indebted to the Greek words attache (elsewhere) and aisthanesthai (to notice, to perceive). They translate loosely as 'seeing in a different place'. All four terms are used to denote the illusory projection of a regular sense perception from one quadrant of the visual field to the diagonally opposed quadrant (hence the name fata morgana of the visual sphere). For example, a person with visual allachaesthesia may perceive a visitor standing on the right as standing in an inverted position on the left, as if this person were trodding on the ceiling. The German term optische Alloästhe-sie (i.e. optical alloaesthesia) was introduced in or shortly before 1928 by the Austrian neurologist and psychiatrist Otto Pötzl (1877-1962) and his colleague Georg Hermann. The phenomenon itself was described as early as 1895, as witness the autobiographical recording of this phenomenon by the German neurologist Ernst Beyer. As Beyer reports, he himself experienced visual allachaesthesia in the wake of one of his migraine attacks. He saw houses and a church in his left visual field, which were actually present on his right-hand side. In Beyer's case, the phenomenon was accompanied by a blurring of vision in the lower left quadrant and a * scotoma developing from the periphery towards the central field of vision. Visual allachaesthesia tends to occur in the context of visuospatial neglect, usually due to a lesion to the right parietal lobe. However, it has also been described in hysteria, in the context of *aurae preceding migraine attacks, and in association with lesions affecting the occipital lobe. Visual allachaesthesia is commonly classified as a *metamorphopsia, which is itself classified as a *sensory distortion. Visual allachaesthesia should not be confused with *inverted vision, a condition in which objects of fixation, or the entire extracorporeal environment, are perceived as if rotated 180o.ReferencesBeyer, E. (1895). Uber Verlagerungen im Gesichtsfeld bei Flimmerskotom. Neurologische Zentrallblatt, 14, 10-15.Critchley, M. (1939). Visual and auditory hallucinations. British Medical Journal, 2, 634-639.Halligan, P.W., Marshall, J.C., Wade, D.T. (1992). Left on the right: Allochiria in a case of left visuo-spatial neglect. Journal of Neurology, Neurosurgery and Psychiatry, 55, 717-719.Hermann, G., Pötzl, O. (1928). Die optische Alloästhesie. Berlin: S. Karger.Klee, A., Willanger, R. (1966). Disturbances of visual perception in migraine. Acta Neurolog-ica Scandinavica, 42, 400-414.
Dictionary of Hallucinations. J.D. Blom. 2010.
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allachaesthesia — Also known as allachesthesia, allesthesia, allaesthesia, allochaesthesia, allochesthesia, alloesthesia, and atopognosis. The term allachaesthesia comes from the Greek words allache (elsewhere) and aisthanesthai (to notice, to perceive). It… … Dictionary of Hallucinations
optical allachaesthesia — see visual allachaesthesia … Dictionary of Hallucinations
fata morgana of the visual sphere — see visual allachaesthesia … Dictionary of Hallucinations
metamorphopsia — The term metamorphopsia comes from the Greek words metamorphoun (to change the form) and opsis (seeing). It translates roughly as seeing an altered form . It is not clear who introduced the term, but it appears in a medical lexicon as early as … Dictionary of Hallucinations
fata morgana — Fata morgana is Italian for mirage. The eponym is derived from Morgan le Fay, the name of King Arthur s half sister, a fairy and shape shifter who features in the Legend of the Grail.The term fata morgana is used to denote a complex type of… … Dictionary of Hallucinations
inverted vision — Also known as reversal of vision metamorphopsia. The term inverted vision comes from the Latin words inverto (to turn around, to change) and visio (seeing). It is used to denote a rare visual phenomenon in which objects of fixation, and… … Dictionary of Hallucinations
optical alloaesthesia — see visual allachaesthesia … Dictionary of Hallucinations
optical allochiria — see visual allachaesthesia … Dictionary of Hallucinations
allochiria — Also known as allocheiria. Both terms stem from the Greek words allos (other) and cheir (hand), translating loosely to other hand . The term allochiria was introduced in or shortly before 1882 by the Austrian neuroanatomist and… … Dictionary of Hallucinations