Tongue- and Jaw-Specific Contributions to Acoustic Vowel Contrast Changes in the Diphthong /ai/ in Response to Slow, Loud, and Clear Speech

Abstract

Purpose: This study sought to determine decoupled tongue and jaw displacement changes and their specific contributions to acoustic vowel contrast changes during slow, loud, and clear speech.

Method: Twenty typical talkers repeated "see a kite again" 5 times in 4 speech conditions (typical, slow, loud, clear). Speech kinematics were recorded using 3-dimensional electromagnetic articulography. Tongue composite displacement, decoupled tongue displacement, and jaw displacement during /ai/, as well as the distance between /a/ and /i/ in the F1-F2 vowel space, were examined during the diphthong /ai/ in "kite."

Results: Displacements significantly increased during all 3 speech modifications. However, jaw displacements increased significantly more during clear speech than during loud and slow speech, whereas decoupled tongue displacements increased significantly more during slow speech than during clear and loud speech. In addition, decoupled tongue displacements increased significantly more during clear speech than during loud speech. Increases in acoustic vowel contrast tended to be larger during slow speech than during clear speech and were predominantly tongue-driven, whereas those during clear speech were fairly equally accounted for by changes in decoupled tongue and jaw displacements. Increases in acoustic vowel contrast during loud speech were smallest and were predominantly tongue-driven, particularly in men.

Conclusions: Findings suggest that task-specific patterns of decoupled tongue and jaw displacement change and task-specific patterns of decoupled tongue and jaw contributions to vowel acoustic change across these speech modifications. Clinical implications are discussed.

Figure 1.

(a) A model of the relations between decoupled tongue and jaw displacements and the resulting tongue composite displacement (circular isoline). (b) Hypothetical framework for predicted changes in decoupled tongue and jaw displacement, as well as the changes in tongue composite displacements for productions of the diphthong /ai/ in response to slow, loud, and clear speech. Changes in the angular displacement from the x-axis θ indicate the relative contribution of the decoupled tongue and jaw to the tongue composite displacement along the isoline. The angle also indicates articulator-specific contributions to acoustic contrast change with an angle close to 0° indicating predominantly jaw-driven vowel acoustic change, an angle close to 90° indicating predominantly tongue-driven vowel acoustic change, and an angle around 45° indicating tongue- and jaw-driven vowel acoustic changes.

Figure 2.

An example of jaw and posterior tongue composite movement during the diphthong /ai/ produced during clear speech by a female talker. Note that only movement in the sagittal plane was used in this figure although 3D kinematic data were recorded and 3D Euclidean distances between onset and offset (indicated by unfilled circles) were calculated for both articulators.

Figure 3.

Group means (± SE) for decoupled tongue displacements (a), jaw displacements (b), composite movements of the tongue (c), and acoustic vowel contrast (d) across all speech conditions. Brackets indicate significant pairwise comparisons.

Figure 4.

Acoustic vowel contrast changes as a function of jaw displacement changes (top) and decoupled tongue displacement changes (bottom). Filled circles are female talkers; unfilled circles are male talkers.

Figure 5.

Testing the hypothetical framework across all participants (a), in female talkers (b), and in male talkers (c). Mean decoupled tongue and jaw displacements (± SE) for each speech modification and the tongue composite displacement (dashed colored lines).

Figure 6.

Task-dependent changes of /a/ and /i/ positions in the F1–F2 vowel space. Mean F1 and F2 values for all talkers (a), female talkers (b), and male talkers (c) are provided. Error bars are omitted to improve readability of the figure. Blue lines indicate change from typical speech to the specific speech modification.