Several patients of P. J. Vogel who had undergone cerebral commissurotomyfor the control of intractable epilepsy were tested ona variety of tasks to measure aspects of cerebral organizationconcerned with lateralization in hemispheric function. From testsinvolving identification of shapes it was inferred that in the absenceof the neocortical commissures, the left hemisphere still has accessto certain types of information from the ipsilateral field. The majorhemisphere can still make crude differentiations between variousleft-field stimuli, but is unable to specify exact stimulus properties.Most of the time the major hemisphere, having access to some ipsilateral stimuli, dominated the minor hemisphere in control of the body.
Competition for control of the body between the hemispheres isseen most clearly in tests of minor hemisphere language competency,in which it was determined that though the minor hemisphere does possesssome minimal ability to express language, the major hemisphereprevented its expression much of the time. The right hemisphere wassuperior to the left in tests of perceptual visualization, and thetwo hemispheres appeared to use different strategies in attempting tosolve the problems, namely, analysis for the left hemisphere andsynthesis for the right hemisphere.
Analysis of the patients' verbal and performance I.Q.'s, as wellas observations made throughout testing, suggest that the corpuscallosum plays a critical role in activities that involve functionsin which the minor hemisphere normally excels, that the motor expressionof these functions may normally come through the major hemisphereby way of the corpus callosum.
Lateral specialization is thought to be an evolutionary adaptationwhich overcame problems of a functional antagonism between theabilities normally associated with the two hemispheres. The tests ofperception suggested that this function lateralized into the mutehemisphere because of an active counteraction by language. Thislatter idea was confirmed by the finding that left-handers, in whomthere is likely to be bilateral language centers, are greatlydeficient on tests of perception.
