Auditory vocabulary of the right hemisphere following brain bisection or hemidecortication

Unilateral scores of two commissurotomy and three (one left and two right) hemispherectomy patients were obtained on standardized auditory language comprehension tests which use pointing responses to a pictorial array. Unilateral performance by the commissurotomy patients was achieved by restricting the pictorial array to one visual half field, using a novel contact lens system which permits ocular scanning of the lateralized stimulus and self-monitoring of task performance. Using the Peabody and Ammons Picture Vocabulary Tests, the auditory vocabulary in the disconnected or isolated right hemispheres was found to be equivalent to that of normal subjects of ages 8:1 to 16:3 with a mean of 11:7 (eleven years and 7 months old). At the same time, standardized aphasia tests showed that the picture vocabulary in the right hemispheres is similar to that of a heterogeneous population of aphasics, even though the right hemispheres did not behave quite like any classical aphasic diagnostic group. No significant differences were found between right hemisphere comprehension of object vs. action names. Results indicated that vocabulary as a function of word frequency followed the same pattern in the right and left hemisphere although the right hemisphere was consistently lower. This parallel between the two hemispheres was conjectured to reflect some similar or even shared lexical structures in the two hemispheres. Together with other data on the performance of the right hemisphere on the Token Test (Zaidel, 1976), the results suggest a complex model of the development of language laterality in the brain, in which some, but not all, auditory language functions continue to develop in the right hemisphere past what is generally regarded as the critical period for language acquistion. In general, auditory language comprehension is better characterized as that of an "average aphasic" than that of a child of a specific age.