Abstract
Levy's hypothesis of ipsilateral motor control of the lateral distal musculature in left handers employing an inverted handwriting posture was tested in a true simple reaction time paradigm. Left-handers employing a non-inverted handwriting posture (NHP) showed performances consistent with normal (contralateral) motor control organization. Inverted handwriting posture (IHP) sinistrals showed performances that were not consistent with Levy's hypothesis nor with the simple hypothesis of normal (contralateral) control. The results for IHP sinistrals were compatible with a model of stimulus-response mediation which posits contralateral motor control and an intrahemispheric “disconnection” of left hemisphere visual areas from left hemisphere manual motor areas. The hypothesis that IHP sinistrals must utilize interhemispheric pathways for motor responses to stimuli channeled to, or formulated in, the left hemisphere was discussed in relation to the hypothesis of topographic inversion consequent to transcallosal relay. The proposed model suggests that hand inversion in writing is an accommodation to the consequences of interhemispheric relay and not to ipsilateral motor control.
Published Version
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