Right hemisphere comprehension of verbs in patients with complete forebrain commissurotomy: Use of the dichotic method and manual performance

The paradigm of dichotic listening was used to investigate verbal comprehension in the right, so-called “nonverbal,” hemisphere. Verbal commands were presented to the right and left ears in the simultaneous (dichotic) paradigm. There were striking instances, especially when the left hemisphere was occupied with some extraneous task, in which the right hemisphere understood the verbal command and executed the appropriate motor responses. In those instances the left hemisphere gave no overt response. Although the left hemisphere was usually dominant, it can be nevertheless concluded that not only can the right hemisphere understand verbal commands but can also express itself manually by executing actions more complex than object retrieval or pointing. As has been known for some time, the blockage of the ipsilateral pathway seems so complete during dichotic listening in the commissurotomy patient that there is no report of the words in the left ear—only of those presented to the right. At the same time there is normal report when words are presented to the left ear alone. It was found in the present study, however, that this model is too simple and only applies to the verbal response paradigm of dichotic listening. Under circumstances of dichotic presentation where the stimulus in the left ear (ipsilateral pathway) is necessary or important to the left hemisphere for completing a task, words from both pathways are reported. One may conclude that there exists a gating mechanism in each hemisphere that controls the monitoring of each auditory pathway and the degree of ipsilateral suppression.     

The morphological asymmetry of the hemispheres and cerebral dominance for speech: A possible relationship

The asymmetry of the posterior Sylvian branches of the middle cerebral artery was examined on the carotid angiograms of 59 patients in whom the lateralization of speech representation was known from sodium amobarbital (Amytal) studies. The usual asymmetry of these vessels was found to be present in the group of patients with left-hemisphere speech representation but significantly reduced in patients with atypical cerebral dominance for speech. A model of the inheritance of handedness and cerebral dominance is extended to take account of these results.     

Shift of visual field preference for Hebrew words in native speakers learning to read

Lateralization for Hebrew words was tested in both the visual and auditory modalities in Israeli children learning to read their native language, Hebrew. A left visual field preference for tachistoscopically presented words was found in the second graders in contrast to a right visual field preference for the same words in the third graders. Children in both grades showed a right ear dominance for similar words presented dichotically. These data suggest right hemisphere involvement in acquiring reading skills of a native language.     

Developmental auditory agnosia in the severely retarded: A further investigation

The hypotheses were investigated that (a) ability to recognize the auditory perceptual stimuli for familiar events is a developmental correlate to language acquisition and (b) the low functioning mentally handicapped suffer from auditory agnosia and are impaired in this ability. The subjects were 42 nonretarded children of ages 3 through 6 and 53 severely and moderately retarded, noninstitutionalized students. The retarded subjects were matched by mental age to the chronological age of the nonretarded children. The stimuli were 49 environmental sounds; the task consisted of sound-and-picture matching-to-sample. Group membership and developmental age were the factors in an analysis of variance design. The results revealed a strong effect of developmental age (p <. 0001). The effect of group was not significant, indicating that auditory agnosia may not be common among the lower functioning retarded. The assumption that agnosia may be a major factor underlying the language disability of the severely retarded was reexamined. It was suggested that the severely retarded achieve the requisite perceptual-semantic knowledge base for language too late, after the critical age for spontaneous and efficient language learning has passed.     

Cognitive task effects on hemispheric blood flow in humans: Evidence for individual differences in hemispheric activation

Evidence from two indirect measures of hemispheric activity, EEG α and conjugate lateral eye movements, has pointed to the existence of individual differences in hemispheric activation. Results from a more direct indicator of hemispheric activity, regional cerebral blood flow as measured by the ¹³³Xe inhalation method, show that such individual differences can be detected in the distribution of blood in the two hemispheres and that the amount of increase in blood flow in the right relative to the left hemisphere is correlated with performance on a spatial task. These results corroborate and extend the findings from the EEG and eye movement studies and suggest that the dimension of individual differences in hemispheric activation may exert significant influence on cognitive performance and on problem-solving strategies.     

Regional cerebral blood flow response to recognition memory versus semantic classification tasks

Two randomly assigned groups, N = 7 each, of neurologically normal patients were composed. One group, RM, had regional cerebral blood flow measurements during a recognition memory probe test; the other group, SC, had rCBF measurements during a semantic classification task, using the same stimulus and response features as the RM task. Thus, the groups differed only in the cognitive instruction they were executing. The RM group showed a significantly lower change from resting baseline to activation, in mean left hemisphere initial slope index, than did the SC group. The RM group, but not the SC group, showed a significant inverse correlation between occipital flow and accuracy of memory performance as indicated by d′. Correlations between age and hemispheric initial slope index, and between homologous left and right hemisphere sites, were also described. The results are considered to support an anatomical basis for the distinction between episodic and semantic memory and to suggest that occipital flow may diminish with accurate memory performance because of an upstream demand of blood in the medial temporal lobes.     

The effect of set size on hemifield asymmetries in letter recognition

Single letters were presented tachistoscopically in the left or right hemifield to right-handed observers. Superior recognition of letters on the right was found for letters chosen from subsets containing four items, but no differences were found when any letter, or any symmetrical letter, could appear. In a second experiment, the right hemifield advantage was found under conditions requiring the subject to determine the subset only when the subset chosen was appropriate. Results were discussed in terms of the adequacy of language-based explanations of hemifield asymmetries in letter recognition.     

Auditory processing of brain-damaged adults under competitive listening conditions

Right CVAs, mild left CVAs, and non-brain-damaged adults received the Token Test under three conditions: quiet, white noise, and speech babble. Left CVAs performed most poorly of all groups in all conditions experiencing difficulty with subtests III, IV, and V. Right CVAs were inferior to controls on each of these three subtests in the speech babble condition only. Thus, right CVA difficulty with both memory and syntactic tasks was demonstrated in speech babble. These results are explained by the hypothesis that both hemispheres are necessary to process auditory information under complex listening conditions. Total brain capacity of right CVA patients may be overloaded if either memory load or linguistic complexity is increased in the presence of certain types of listening competition.     

Right-hemisphere speech representation and comprehension of syntax after left cerebral injury

Comprehension of language and visuo-spatial abilities were studied in 12 surgical patients with left cerebral lesions and right-hemisphere speech representation verified by sodium amobarbital tests. When left-hemisphere symptoms preceded the acquisition of speech, impaired understanding of syntactically complex sentences was associated with an early, but not late, onset of convulsive seizures. Other behavioral measures did not show a similar effect of age at seizure onset. Sparing or loss of comprehension could not be related to any aspects of the neurological histories in cases with right-hemisphere speech acquired before the onset of left-hemisphere symptoms. Factors which may have influenced the development of right-hemisphere language comprehension are discussed.