Sinistral inverters do no possess an anomalous visuomotor organization

Abstract

Moscovitch and Smith (Science 205, 710-713, 1979, and Neuropsychologia 17, 637-644, 1979), while failing to confirm Levy and Reid's general hypothesis that sinistrals writing with an inverted posture have predominantly uncrossed or ipsilateral motor pathways, nevertheless reported that they possess an unusual visuomotor organization. We incorporated an extra (arm-across-the-midline) condition into a version of their study. Not only could we not replicate their original findings, but we believe that their data may have been contaminated by spatial compatibility effects which require the crossed-arm condition for elimination. Sinistral inverters in fact appear to have exactly the same motor and visuomotor organization as noninverters and dextrals. A value of 4 msec for transcommissural transmission times was obtained, which corresponds well with other electrophysiological and behavioral estimates.