As the name implies, mirror writing is a mirror image of normal writing, hence running from right to left, with characters back to front. This may occur spontaneously, apparently more often in left-handers, or in right-handers attempting to write with the left hand following left-sided brain injury (e.g., stroke).
Leonardo da Vinci is the most celebrated mirror writer: it is possible his left-handedness, and hence mirror writing, followed an injury to his right hand. The author Lewis Carroll occasionally wrote mirror letters but these differ from his normal script, unlike the situation with Leonardo whose two scripts are faithful mirror images. Carroll’s letters may thus reflect not an inherent capacity but a contrivance, designed to amuse children who corresponded with him. The device was also used by the author Arthur Ransome in his 1939 novel Secret Water. Jane Austen wrote one letter (1817) to a young niece in which script runs from right to left but with word order reversed within words (i.e., not mirror writing).
Various neural mechanisms are proposed to explain mirror writing, including bilateral cerebral representation of language, motor programs or visual memory traces or engrams. The mechanisms may differ between a true mirror writer like Leonardo and someone performing the task for amusement like Carroll.
Double mirror writing (écriture en double miroir) is inverted top to bottom (i.e., script goes up the page, upside down) in addition to being mirror reversed.
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