Mirror Writing Across Cultures: motor hypothesis vs. directional apraxia in dextrad and sinistrad writers
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‘Mirror writing’ – the production of backwards facing script - occurs frequently in semi-literate children with the dominant right hand, and involuntarily with the non-dominant left hand amongst brain damaged adults, and both involuntarily and intentionally under experimental conditions. Its underlying theoretical mechanisms are disputed; whilst the classic motor hypothesis posits mirror writing to be a consequence of the non-dominant hand reversing dominant hand canonical writing motor sequences, directional apraxia claims it is the product of a directionality malfunction, resulting in a reversion to innately preferred outwards movements, regardless of handedness. Although both theories hypothesise more reversals with the left hand amongst dominant right-handers in dextrad (left-to-right) scripts, their predictions for sinistrad (right-to-left) scripts differ. Following anecdotal reports of cognitive load inducing mirror writing (Fuller, 1916;Critchley, 1928), an audio-visual dual task was designed, with naïve English speaking Arabic sinistrad (N=11) and dextrad (N=11) bilinguals simultaneously executing the Eriksen Flanker Task (Eriksen & Eriksen, 1974) and dictated letter transcription on a digitalising touchscreen. Writing on a table under-side - known to yield mirror writing - was briefly studied, with the introduction of the un-investigated manipulation of left hand writing. Participants performed secondary dexterity and directionality tasks, to observe any script culture effects, though most differences between groups were marginal or non-significant. Whilst the dual-task effectively induced mirror writing, script direction had no effect, indicating the superiority of the classic motor hypothesis in experimentally produced mirror writing in healthy adults.