Investigations on Lateralization of Function in the Disconnected Hemispheres of Man

Citation

Nebes, Robert David (1971) Investigations on Lateralization of Function in the Disconnected Hemispheres of Man. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AA8W-SC34. https://resolver.caltech.edu/CaltechTHESIS:06082018-123956199

Abstract

The effect of long standing cerebral damage upon the pattern of functional lateralization revealed by division of the forebrain commissures was investigated in a young conunissurotomy patient with birth injury to the somato-sensory region of his left hemisphere. Results from a battery of sensory - motor tasks showed that, unlike previous conunissurotomy cases, the major hemisphere of this subject had access to somesthetic information from the ipsilateral as well as the contralateral hand, thus allowing him to name objects out of sight in his left hand, and to use this hand to tactually find items, the pictures or names of which had been visually presented to only the left hemisphere. The most plausible explanation for these exceptional cross integrative abilities would be the presence of a left sided ipsilateral somesthetic projection, which, in compensation for the subject's early brain damage, has strengthened into a functional system. Additional evidence for compensatory reorganization in this boy was found in his minor hemisphere, which exhibited an enhanced capacity for expressive language, being capable of transcribing printed words into script6 and, upon occasion, of writing the name of an object.

Further research into the lateralization of higher intellectual functions in man involved a study of the psychological processes responsible for the superiority of the right side of the brain on certain perceptual activities. The minor hemisphere, in the several commissurotomy patients tested, was found to excel the major on tasks involving visualization, from incomplete or disjointed sensory data, of the total stimulus configuration: this was revealed by its supremacy on such problems as: judging from a tactual or visual inspection of an arc, the size of the circle from which it had come, or mentally reconstructing the contour of a geometric shape seen in a fragmented state, or perceiving the pattern inherent in a visual display due to the differential spacing of its components. Extension of this testing to normal persons established that competency in the handling part-whole relationships is, in some manner, correlated with handedness, as left handed individuals performed much worse than right handed ones.

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