The effect of oral articulation on the acoustic characteristics of nasalized vowels

To study the acoustic characteristics of nasalized vowels, the effects of velopharyngeal opening and oral articulation are considered. Based on vocal tract area functions for one American English speaker, spectral evolutions for the nasalization of three English vowels /a/, /i/, and /u/ were studied by simulating transfer functions for vowels with only velar movement, and for different nasal consonant-vowel utterances, which include both velar and oral movements. Simulations indicate extra nasal spectral poles and zeros and oral formant shifts as a result of the velopharyngeal opening and oral movements, respectively. In this sense, if oral articulation is coordinated with velar movement in such a way that nasal acoustic features are prominently attenuated, corresponding compensatory articulation can be developed to reduce hypernasality. This may be realized by (1) adjusting the articulatory placement for isolated nasalized vowels or by (2) changing the relative timing of coarticulatory movements for dynamic speech. The results demonstrate the effect of oral articulation on the acoustics of nasalized vowels. This effect allows oral articulation to compensate for velopharyngeal dysfunction, which may involve a constellation of speech production disorders resulting from anomalous velopharyngeal closure and which is usually accompanied by hypernasality and nasal emission of air.