A Dichotic Threshold Test: Normal and Brain-Damaged Subjects When two speech sounds are presented simultaneously to the two ears, normal subjects were able to report accurately the input to either ear until the signal amplitude to the unattended ear exceeded that to the attended ear by 15 dB—the dichotic threshold. While the right ear and left ear thresholds ... Research Article
Research Article  |   March 01, 1971
A Dichotic Threshold Test: Normal and Brain-Damaged Subjects
 
Author Affiliations & Notes
  • Robert A. Dobie
    Stanford University, Stanford, California
  • F. Blair Simmons
    Stanford University, Stanford, California
Article Information
Research Articles
Research Article   |   March 01, 1971
A Dichotic Threshold Test: Normal and Brain-Damaged Subjects
Journal of Speech, Language, and Hearing Research, March 1971, Vol. 14, 71-81. doi:10.1044/jshr.1401.71
History: Received May 15, 1969
 
Journal of Speech, Language, and Hearing Research, March 1971, Vol. 14, 71-81. doi:10.1044/jshr.1401.71
History: Received May 15, 1969

When two speech sounds are presented simultaneously to the two ears, normal subjects were able to report accurately the input to either ear until the signal amplitude to the unattended ear exceeded that to the attended ear by 15 dB—the dichotic threshold. While the right ear and left ear thresholds were never more than 15 dB apart in 33 normal subjects, six of 10 patients with unilateral brain damage showed interaural performance differences ranging from 48 to 110 dB. Six patients had non-dominant cerebral lesions, and of these, four showed markedly superior performance by the ear opposite the intact dominant hemisphere. Two of the four aphasic patients also showed large asymmetries, favoring the ear contralateral to the lesion in one case, and the ipsilateral ear in the other.

In 17 normal right-handed subjects, the mean dichotic threshold when the right ear was attended exceeded that obtained for the left ear by 4.8 dB (p < 0.01). In a group of 16 left-handed subjects, there was a slight tendency to superior performance by the left ear (1.3 dB, p < 0.20).

These results suggest a role for the nondominant hemisphere in processing and/or storage of competing speech stimuli.

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