Abstract
Objective: In this longitudinal study, we investigated the hypothesis that kinematic measures of jaw movement produced by children who stuttered (CWS) and children who did not stutter (CWNS) would differ between opening and closing speech gestures, across phonetic contexts, and across development. Methods: Mean amplitude, velocity, and duration of jaw opening and closing gestures during repeated productions of bilabial syllables were analyzed longitudinally at 1-year intervals for 13 CWS and 7 children CWNS. The utterances ranged across four phonetic contexts: single-syllable, two-syllable, three-syllable, and six-syllable. For jaw movement transduction, a strain gauge was attached to a football helmet in a novel design to minimize head movement. All kinematic measures were made from jaw movement tracings in Windaq (Dataq Instruments, Inc.) software, based on a standard millimeter to voltage conversion. Results: The main finding of the study was that opening gestures were produced by both CWS and CWNS with greater amplitude and duration compared to closing gestures. However, the kinematics associated with opening and closing jaw movements did not differ between CWS and CWNS, suggesting that the intrinsic articulatory dynamics of the two groups were similar. In addition, adapting the kinematics of opening and closing jaw movements across the four phonetic contexts did not differ between the groups for either movement amplitude or velocity. However, CWS produced the closing gesture with significantly greater duration compared to multi-syllable conditions, relative to CWNS. Finally, CWS and CWNS exhibited different longitudinal patterns for jaw amplitude and peak velocity. Conclusion: The speech motor systems of CWS and CWNS exhibited broadly similar organization of intrinsic articulatory dynamics, but groups may differ in how underlying dynamics are adapted to changing phonetic contexts across development. It is possible that the speech fluency of CWS might benefit from greater articulatory constraints, as the main between-group difference was identified when degrees of freedom of movement were greatest. Implications of findings are discussed within the development of a hierarchically organized speech motor system.
Highlights
The speech motor skills of children and adults who stutter have been investigated in search of potential speech motor factors in developmental stuttering [1,2]
Observations were made for 2 gestures, across 4 levels of phonetic length, and across 3 time points, and kinematic measures made for each observation correspond to the waveform presented in (Figure 3)
Gesture amplitude First, no main effect was found for group, with children who stutter (CWS) exhibiting similar amplitude compared to children who did not stutter (CWNS), but a main effect was found for gesture, with the opening gesture having overall greater amplitude compared to the closing gesture, t(310)=5.772, p
Summary
The speech motor skills of children and adults who stutter have been investigated in search of potential speech motor factors in developmental stuttering [1,2]. Peak velocity, and duration across jaw opening and closing gestures were compared across four levels of phonetic length and three time points. The time to peak velocity of closing movements across articulators (e.g. lower lip, upper lip, and jaw) is highly correlated, providing evidence of coordinative relations among articulators [9]. Opening and closing movements differ across speaking rates, which may be interpreted as different functional organization across changing phonetic goals [10] Such evidence points to a hierarchical organization of the speech motor system [11, 12] such that the intrinsic dynamics of the speech motor system flexibly adapt to higher-level phonetic goals (e.g syllable stress)
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