Mirror-writing, whether produced by movements of the right or of the left hand, may be defined simply as script that runs in a counterclockwise direction. An early example of such writing is found in the well known report that Leonardo da Vinci habitually wrote in this reversed fashion and that most of his anatomic sketches exhibit marginal annotations written from right to left; indeed, on the strength of this evidence it has been assumed that the master was left-handed. This conclusion, however, appears to be by no means an inevitable one, as experience seems to show that not a few dextral persons through secret practice acquire the faculty of being able to produce reversed script with the right hand.
Because it constitutes a borderline problem, interesting alike to medical men and to psychologists, this graphic peculiarity has been the subject of an extremely copious literature. Useful working lists of the
QUINAN C. INVOLUNTARY GRAPHIC SPRAWLA MOTOR PHENOMENON RELATED TO MIRROR-WRITING AND MODIFIED BY THE FACTOR OF HANDEDNESS. Arch NeurPsych. 1935;34(2):318-329. doi:10.1001/archneurpsyc.1935.02250200078007