Acoustic characteristics of lexical stress: A study of normally speaking and speech-delayed children

Date of Completion

January 2002

Keywords

Speech Communication

Degree

Ph.D.

Abstract

The acoustic characteristics of normally speaking (NS) and speech delayed (SD) children's production of trochaic and iambic stress were examined. The purpose of this investigation was to extend past research describing lexical stress production in NS children by considering the influence of phonetic composition, utterance position, and production variability. These variables were evaluated in SD children and subsequently compared to NS children. ^ Two groups of six-year-olds (18 children per group) participated. Eight novel disyllabic words (four trochaic and four iambic) varying in phonetic difficulty were taught to each child. Words were elicited three times in both utterance-initial and utterance-final position. Each syllable comprising the words was measured for duration, intensity, and fundamental frequency (F 0). Variability in the acoustic characteristics of stress across word productions was also determined. ^ Results showed significant differences between child groups. Children with SD produced trochaic and iambic words with greater overall intensity and F0, and iambic words with shorter duration, than NS children. The possibility of increased speech effort among the SD group is offered as an explanation for these group differences. For both child groups, utterance-final position altered the duration of trochaic words reflecting an iambic stress pattern, and the intensity and F0 of iambic words reflecting a trochaic stress pattern. The results are consistent with known acoustic effects of lengthening and decreased intensity and F0 at utterance endings. Phonetic difficulty appeared to impact children's use of duration to mark stress. SD children produced trochaic words of high phonetic difficulty with overall longer duration compared to NS children. Regardless of phonetic difficulty, both groups were inaccurate in their use of intensity and F0 to mark iambic stress. Variability analysis showed no child group differences. For both groups, trochaic words were less variable than iambic words with respect to duration and F0, but not intensity. ^ It was concluded that NS children are not as capable of producing lexical stress as previously reported. Children with SD differ from NS children in overall production of lexical stress, but both groups were affected similarly by utterance position and phonetic difficulty. ^

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