Physiological control of sibilant duration: insights afforded by speech compensation to dental prostheses.

Temporal relationships among tongue contact, phonation, and presence of frication were examined for /s/ and /z/. In cases where /s/ and /z/ were produced with a supraglottal articulation of the same duration, the duration of the resulting frication was 17 ms longer for /s/. The difference can be attributed to glottal activity. The presence of a unfamiliar dental prosthesis in the mouth caused the tongue to contact the alveolar ridge sooner and release later. This physiological effect was reflected in lengthening of frication for sibilants, but the acoustical consequences were greater and more reliable for /z/ than for /s/. Reasons for this difference were sought in adaptation of timing of tongue contact, and in aerodynamic conditions expected for voiced versus voiceless sibilants. A rapid adaptation of tongue contact timing was found, with the adaptation being greater for /s/. Timing of vocal fold adduction at the end of unvoiced sibilants, and its aerodynamic consequences, are suggested to consequences, are suggested to contribute to the relative stability of /s/ acoustical durations.