Twenty-six subjects, thirteen stutterers and thirteen fluent speakers, were matched by age, sex and educational background. None had any history of neurosurgery, neuropathology or debilitating injury to the head or neck. Two GRASS silver chloride electrodes were attached to the chin and inferior surface of the lower lip of each subject. This recording site was chosen because, presumably, it would detect activity of the quadratus labii inferioris, a muscle involved in the articulation of labial phonemes, permitting a distinction between the labial and nonlabial ensembles and, therefore, speech and nonspeech oral activity. EMG recordings, measuring covert phonetic activity, were obtained with a GRASS Model 7 polygraph and recorded on a strip printer during a verbal-listening task. Each subject heard ten groups of five words each. Five of the ten word-groups were comprised of words with bilabial sounds (/p/, /b I, /m/). The other five groups had words without bilabial sounds. The subjects were instructed to attempt memorization of each word-group as it was presented, as they may be asked to write the words on paper shortly after each presentation. The electromyography print-outs were divided into two ten-second categories: First, presentation which coincided in real time with the subject's auditory reception of each word group; second, rehearsal which coincided in real time with the subject's attempt to retain the word group in auditory memory before being instructed to write down the words heard or wait for the next word-group presentation. Statistical analyses of the electromyograms revealed no significant group differences between stutterers and fluent speakers; however, highly significant individual differences were found when experimental subjects were compared one-by-one with their controls. Fifty-four percent (seven pairs) of the experimental subjects were significantly more active subvocally during presentation and rehearsal of labial and nonlabial word groups than their control. In twenty-three percent (three pairs), the experimental subjects were significantly less active subvocally. The remaining twenty-three percent (three pairs) were not significantly different from each other in subvocal activity. The terms "hyperactive-subvocalizer," "hypoactive-subvocalizer" and "active-subvocalizer" were coined for use in labeling subjects who were relatively more active, less active or normally active subvocalizers. It was concluded that seventy-seven percent of the stutterers in the present research study showed aberrant subvocal articulatory patterns. It was suggested that analysis of subvocalization patterns may be used as part of a differential diagnostic test battery to aid in identification of a neurogenic component as part of an individual stutterer's communicative disability.
Speech Pathology and Audiology, Stuttering; Stuttering--Case studies; Stuttering--Child. Laterality; Laterality--Case studies.
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