Handwriting posture, visuomotor integration, and lateralized reaction-time parameters.

On a simple manual reaction-time (RT) task to lateralized visual signals, right-handers and left-handers with the noninverted handwriting posture (RN and LN subjects, respectively) were faster and more consistent when the signal and response hand were homolateral as compared to heterolateral, but left-handers with the inverted handwriting posture (LI subjects) were not. For LI subjects, there was no speed difference for homolateral and heterolateral hand-signal combinations, and there was a clear and significant heterolateral superiority for response consistency. In agreement with suggestions of others, we believe that the anomalous response pattern of LI subjects is likely to be due to a disorder of visuomotor integration and cannot be attributed to reliance on uncrossed motor pathways.