Frontiers in Psychology (Apr 2014)
Duration of content and function words in oral discourse by speakers with fluent aphasia: Preliminary data
Abstract
Introduction Literature on word access during oral production has suggested that content and function words are generally accessed differently, as reflected by a shorter word durations in oral production of functors (Bolinger & Sears, 1981). This difference in word durations among typical speakers reflects the rate of lexical access, which is mediated by a general mechanism coordinating the pace of higher-level lexical activations and the execution of the articulatory planning (Bell, Brenier, Gregory, Girand, & Jurafsky, 2009). Depending on the aphasia syndrome, speakers with aphasia should demonstrate varied degree of impairment in lexical (content and/or function) access. The current study aimed to examine whether speakers with aphasia would demonstrate a similar discrepancy of word durations for content and function words. Methods Language samples and their corresponding audio files were collected from 17 Cantonese-speaking individuals with fluent aphasia (fifteen anomic, one transcortical sensory, and one Wernicke’s). Seventeen gender-, age-, and education-matched controls also participated. Using the Cantonese AphasiaBank protocol, each subject provided narrative samples elicited by tasks of personal monologue, picture and sequential description, and story-telling. Following the procedures proposed in Lee, Kong, Chan, and Wang (2013), automatic time alignment was performed on each audio recording according to the manual orthographic transcription. All non-speech and unintelligible speech segments were excluded for alignment. The results of time alignment included the beginning and end time of all sub-syllable units in the utterance, from which the duration of words could be computed. Descriptive analysis was performed on the duration of content and function words in aphasia and normal speech. Results and Discussion Words that had occurred ten times or more in the speech materials was arbitrarily categorized as ‘unique words’ that could more reliably reflect syllable duration. There were a total of 206 unique words (141 content and 65 function words) in the aphasia speech materials and 253 unique words (187 content and 66 function) in the normal materials, most of them were disyllabic or monosyllabic. A higher lexical diversity in the normal group, but similar number of different function words for both groups, was consistent with earlier findings of impaired lexical access in aphasia. Table 1 displays the average duration per syllable and per word for content and function words among the two speaker groups. Our study showed that word duration in aphasic speech was longer than that in control speech. This is in line with our earlier results of higher speaking rate in normal speech. While content words were longer than function words in the aphasic speech, the difference was not as significant as that in controls.
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