Speech and Hearing Sciences ETDs

Publication Date

12-5-1973

Abstract

Normal listeners traditionally show a right ear preference for dichotically presented speech stimuli, and a left ear preference for dichotically presented non-speech stimuli. Although some inter-subject variability is observed within and between groups of non-brain damaged subjects, the performance of the group as a whole is rather predictable and homogeneous. However, results from experiments in which brain damaged subjects have been studied have been less straightforward. Although left brain damaged subjects have consistently shown a bilateral deficit in reporting dichotic speech stimuli, a great deal of variability in performance is observed within the groups. Further study of brain damaged individuals, in an attempt to account for this variability, might provide information toward a more thorough understanding of auditory processing. The method of a data analysis applied in these studies might also be an important factor in answering this question. Accordingly, the purpose of this investigation was to compare the performance of a group of aphasic individuals with a group of normal, control subjects, on a dichotic CV-syllable listening task. In addition, two methods of data analysis, the traditional R-L method and the Percent­of-Errors (POE) method, were evaluated. In comparing the aphasic with the non-aphasic group, the aphasics showed a bilateral deficit in reporting the dichotic CV-syllables. In addition, the non-aphasic group showed a significant right ear advantage for the CV-syllables, while the aphasic group showed a non-significant right ear advantage for the stimuli. However, in view of the fact that six of the aphasics showed a right ear advantage and five showed a left ear advantage for the dichotic CVs, the two aphasic subgroups were analyzed separately. On the basis of single correct item analysis, the superior ear within each aphasic subgroup was found to perform better than the respective ear within the control group. Finally, R-L and POE methods of data analysis were found to correlate very highly. These results were interpreted in view of a functional model which assumed more efficient contralateral auditory pathways and the presence of bilateral auditory processors and a unilateral speech processor. In accordance with this model, the bilaterally depressed ear scores of the aphasic group exhibited in response to the dichotic stimuli were explained by the presence of a lesion in the dominate left hemisphere, interfering with the processing of auditory signals from both ears. Secondly, the right ear advantage for the dichotic syllables within the control group was felt to reflect the greater efficiency of contralateral auditory pathways, as well as the specialized function of the left hemisphere in processing speech. The right ear advantage found within one aphasic subgroup was explained by a lesion interfering with the corpus callosal tract after entering the left hemisphere; the left ear advantage exhibited by the other aphasic subgroup was explained by a lesion in the area of the auditory processor of the left hemisphere. Finally, only one method of data analysis, either R-L or POE, seems necessary since both measures relate the same information about an individual's performance on a dichotic listening task.

Degree Name

Speech-Language Pathology

Level of Degree

Masters

Department Name

Speech and Hearing Sciences

First Committee Member (Chair)

William John Ryan

Second Committee Member

Max Edgar McClellan

Third Committee Member

Richard Baxter Hood

Fourth Committee Member

Bruce Earl Porch

Language

English

Document Type

Thesis

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