palinopsia

   Also referred to as pseudodiplopia. The term palinopsia comes from the Greek words palin (again) and opsis (seeing). It translates as 'seeing again' or 'seeing multiple identical copies'. The original term for this group of visual phenomena was * paliopsia, a neologism introduced in or shortly before 1949 by the British neurologist Macdonald Critchley (1900-1997). In 1954 the spelling was modified to palinopsia by the Austrian neurologist and psychiatrist Otto Pötzl (1877-1962). Both terms refer to a group of visual images that persist or recur paroxysmally after the original object or stimulus has moved out of sight. Palinopsia may present either in the form of multiple repetitions of a single image (called polyopia), in the form of persisting *afterimages (either positive or negative), or as a * trailing phenomenon (i.e. a series of stationary images that trail behind a moving object or stimulus). These images typically last as long as the percipient's gaze is moving or reappear after seconds to minutes. An example of palinopsia given by Critchley runs as follows: "After a person had walked past the foot of the bed from left to right, and then had gone away, she had a moment or two later the impression as if the same person had walked past as before." In a second example, Critch-ley illustrates the variant of the positive afterimage as follows: "If he looks at a thing, and looks away, he may continue to see it. Things he thinks about a lot do not go out of his vision quickly, as if they were slow in being switched off." It has been claimed that palinopsias may also reappear after months or years. In the latter case, they are referred to as * long-latency palinopsias. Conceptually as well as phenomeno-logically, it may be hard - if not impossible - to differentiate long-latency palinopsias from flashback phenomena or * reperceptions. When objects within the visual field take on the colours or patterns of neighbouring objects, the term *illusory visual spread is used. Both phenomena are classified by Critchley as types of * visual per-severation, a phenomenon which is in turn classified as a * reduplicative phenomenon or a type of *metamorphopsia. Equivalents of palinopsia in the auditory and tactile modes of perception are known as * palinacusis (involving the persistence or paroxysmal recurrence of auditory percepts) and * tactile polyaesthesia (involving recurrent tactile sensations), respectively. Pathophysiologi-cally, palinopsia is sometimes conceptualized as a pathological exaggeration of the afterimage. It has also been suggested that palinopsia may be mediated by pathology of the visual parietal regions. Etiologically, the symptom is associated with a variety of conditions, including *aurae (as in the context of paroxysmal neurological disorders such as migraine and epilepsy), hysteria, and the use of * hallucinogens such as mescaline or LSD. It has been suggested that palinopsia may be related in a conceptual and phenomenological sense (and perhaps in a pathophysiological sense as well) to other mnestic events such as * flashbacks occurring in the context of PTSD, drug-related flashbacks, *hallucinogen-induced persistent perception disorder (HPPD), *phantom pain, *reperceptive hallucinations, *eidetic imagery, and *flashbulb memories.

   References

   Critchley, M. (1949). Metamorphopsia of central origin. Transactions ofthe Ophthalmologic Society of the UK, 69, 111-121.

   Critchley, M. (1953). The parietal lobes. London: Edward Arnold & Co.

   ffytche, D.H., Howard, R.J. (1999). The perceptual consequences of visual loss: 'Positive' pathologies of vision. Brain, 122, 1247-1260.

   Pötzl, O. (1954). Über Palinopsie (und deren Beziehung zu Eigenleistungen okzipitaler Rindenfelder). Wiener Zeitschrift für Nervenheilkunde, 8, 161-186.

   Santhouse, A., Howard, R., ffytche, D. (2000). Visual hallucinatory syndromes and the anatomy of the visual brain. Brain, 123, 2055-2064.