Patterns of variance in /s/ during normal and glossectomy speech

The production of speech includes considerable variability in speech gestures despite our perception of very repeatable sounds. Variability is seen in vocal tract shapes and tongue contours when different speakers produce the same sound. This study asks whether internal tongue motion patterns for a specific sound are similar across subjects, or whether they indicate multiple gestures. There are two variants of the sound /s/, which may produce two gestures or may represent a multitude of gestures. The first goal of this paper was to quantify internal tongue differences between these allophones in normal speakers. The second goal was to test how these differences are affected by subjects expected to have different speech gestures: normal controls and subjects who have had tongue cancer surgery. The study used tagged MRI to capture midsagittal tongue motion patterns and principal components analyses to identify patterns of variability that define subject groups and /s/ types. Results showed no motion differences between apical and laminal controls in either the tongue tip or whole tongue. These results did not support unique tongue behaviours for apical and laminal /s/. The apical patients, however, differed from all other speakers and were quite uniform as a group. They had no elevation and considerable downward/backward motion of the tongue tip. This was consistent with difficulty in maintaining the tip–blade region at the proper distance from the palate.