LEFT-RIGHT ASYMMETRY OF CALLOSAL TRANSFER IN NORMAL HUMAN-SUBJECTS

Interhemispheric transfer (IT) of visuomotor information can be assess ed by measuring the crossed-uncrossed difference (CUD) in the Poffenbe rger paradigm [14]. We report a series of experiments aimed at casting light on two aspects of IT: the importance of motor response variable s and the nature of the left-right asymmetries found in a recent meta- analysis of studies using the Poffenberger paradigm [10]. In Experimen ts 1 and 2 we found no effect of varying the finger used for response while there was a larger CUD when using the left hand in comparison to the right hand. In Experiment 3, which employed visual stimuli differ ent from the two preceding experiments, CUD asymmetries were related t o hemifields rather than to hands with a CUD larger for the right than for the left visual hemifield. These findings suggests that both moto r and visual variables are important for CUD asymmetries to occur and are in keeping with a horse race model according to which overall spee d of IT is determined by whichever signal (visual or pre-motor) is mor e rapid in crossing from one side to the other. As to the issue of lat eral asymmetries in the CUD, the results of Expt. 3 have also shown th at asymmetries arise only in tasks requiring an IT and therefore canno t depend upon additive hemispheric effects.