Differences in neural organization between individuals with inverted and noninverted handwriting postures.

Levy's hypothesis that movements of the distal musculature are controlled by ipsilateral motor projections in subjects with inverted writing posture was tested in a reaction-time experiment with lateralized auditory, tactual, and visual stimulation. Subjects were required to depress a response key with the left or right index finger when they detected a stimulus in either the left or right sensory field. Writers with noninverted posture responded quickest to stimuli on the same side as the responding hand in all modalities tested, whereas inverted writers showed this pattern only in auditory and tactual modalities. In the visual modality, they responded quickest to stimuli on the side opposite the responding hand. Because Levy's hypothesis predicts the latter effect in all modalities for inverted writers, it is challenged by our results, which suggest that inverted writers may be characterized by anomalous visual or visuomotor organization.