Unilateral auditory language comprehension on the token test following cerebral commissurotomy and hemispherectomy

Two versions of the Token Test for auditory language comprehension were administered unilaterally to selected commissurotomy and post-infantile hemispherectomy patients. No deficit was found for the left hemisphere while the right showed a severe deficit comparable to that of left brain-damaged asphasics. Error analysis, however, revealed that the right hemisphere was more sensitive to perceptual and (short term auditory verbal) memory constraints in the task, whereas aphasics were more sensitive to linguistic variables. Mean overall scores of the right hemispheres on the Token Test were comparable to 4 yr old children as contrasted with a high mental age estimate—mean 11 yr— on the Peabody Picture Vocabulary Test. It is suggested that in the normally developing brain, distinct language functions exhibit disparate ontogeneses of lateralization in the left hemisphere.