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Coupling dynamics in speech gestures: amplitude and rate influences

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Abstract

Speech is a complex oral motor function that involves multiple articulators that need to be coordinated in space and time at relatively high movement speeds. How this is accomplished remains an important and largely unresolved empirical question. From a coordination dynamics perspective, coordination involves the assembly of coordinative units that are characterized by inherently stable coupling patterns that act as attractor states for task-specific actions. In the motor control literature, one particular model formulated by Haken et al. (Biol Cybern 51(5):347–356, 1985) or HKB has received considerable attention in the way it can account for changes in the nature and stability of specific coordination patterns between limbs or between limbs and external stimuli. In this model (and related versions), movement amplitude is considered a critical factor in the formation of these patterns. Several studies have demonstrated its role for bimanual coordination and similar types of tasks, but for speech motor control such studies are lacking. The current study describes a systematic approach to evaluate the impact of movement amplitude and movement duration on coordination stability in the production of bilabial and tongue body gestures for specific vowel–consonant–vowel strings. The vowel combinations that were used induced a natural contrast in movement amplitude at three speaking rate conditions (slow, habitual, fast). Data were collected on ten young adults using electromagnetic articulography, recording movement data from lips and tongue with high temporal and spatial precision. The results showed that with small movement amplitudes there is a decrease in coordination stability, independent from movement duration. These findings were found to be robust across all individuals and are interpreted as further evidence that principles of coupling dynamics operate in the oral motor control system similar to other motor systems and can be explained in terms of coupling mechanisms between neural oscillators (organized in networks) and effector systems. The relevance of these findings for understanding motor control issues in people with speech disorders is discussed as well.

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Notes

  1. We are aware that repeated measures ANOVA (RMANOVA) and multi-level analysis (ML) are the two default approaches for the analysis of data obtained in repeated measures designs, with the latter approach becoming more popular. However, we refrained from ML-analysis and used RMANOVA because of the restrictions of ML analysis for relatively small sample sizes (Maas and Snijders 2003; Maas and Hox 2005; McNeish and Stapleton 2016) and the fact that the violation of the assumption of compound symmetry can be adjusted by Huynh–Feldt’s epsilon (by downsizing degrees of freedom) as was done in the current analysis (Rietveld and van Hout 2005). As our data analysis file was based on average values across multiple repetitions of the same tokens per condition to use appropriate error degrees of freedom (Max and Onghena 1999), we had no missing data cells for the final analysis, which otherwise would have been a reason to choose the ML approach. A final aspect considered in our choice for using RMANOVA was the availability of partial eta-squared, a well-known index of effect-size.

  2. On request by an anonymous reviewer we also performed a Pearson PM correlation analysis on our data to explore if across the different conditions a relationship between amplitude and relative phase variability could be established. We did indeed find significant negative correlations between SDPHI and both BC amplitudes (r = −0.66, N = 120, p (two-tailed) <0.001) and TB amplitudes (r = −0.60, N = 120, p (two-tailed) <0.001). Since the critical change in relative phase variability occurred specifically at the small amplitudes for the /uːpʊ/ condition, we also performed a Pearson PM correlation analysis without the /uːpʊ/ stimuli, and as expected, the negative correlations values dropped quite a bit, although they were still significant for BC amplitudes (r = −0.43, N = 90, p (two-tailed) < 0.001) and TB amplitudes (r = −0.28, N = 90, p (two-tailed) = 0.007).

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Acknowledgements

We wish to thank Dr. Toni Rietveld for providing statistical advice for data analysis. We also thank Dr. Lieke Peper for her feedback on a previous version of this manuscript. The study reported in this paper was supported by the Natural Sciences and Engineering Research Council (NSERC) and funding from the Canada Research Chairs program, both awarded to the author.

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Correspondence to Pascal H. H. M. van Lieshout.

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van Lieshout, P.H.H.M. Coupling dynamics in speech gestures: amplitude and rate influences. Exp Brain Res 235, 2495–2510 (2017). https://doi.org/10.1007/s00221-017-4983-7

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  • DOI: https://doi.org/10.1007/s00221-017-4983-7

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