Stimulus length on speech stability in ALS (Teplansky et al., 2023)

Purpose: This study aimed to investigate the effect of stimulus signal length on tongue and lip motion pattern stability in speakers diagnosed with amyotrophic lateral sclerosis (ALS) compared to healthy controls.

Method: Electromagnetic articulography was used to derive articulatory motion patterns from individuals with mild (n = 27) and severe (n = 16) ALS and healthy controls (n = 25). The spatiotemporal index (STI) was used as a measure of articulatory stability. Two experiments were conducted to evaluate signal length effects on the STI: (a) the effect of the number of syllables on STI values and (b) increasing lengths of subcomponents of a single phrase. Two-way mixed analyses of variance were conducted to assess the effects of syllable length and group on the STI for the tongue tip (TT), tongue back (TB), and lower lip (LL).

Results: Experiment 1 showed a significant main effect of syllable length (TT, p < .001; TB, p < .001; and LL, p < .001) and group (TT, p = .037; TB, p = .007; and LL, p = .017). TB and LL stability was generally higher with speech stimuli that included a greater number of syllables. Articulatory variability was significantly higher in speakers diagnosed with ALS compared to healthy controls. Experiment 2 showed a significant main effect of length (TT, p < .001; TB, p = .015; and LL, p < .001), providing additional support that STI values tend to be greater when calculated on longer speech signals.

Conclusions: Articulatory stability is influenced by the length of speech signals and manifests similarly in both healthy speakers and persons with ALS. TT stability may be significantly impacted by phonemic content due to greater movement flexibility. Compared to healthy controls, there was an increase in articulatory variability in those with ALS, which likely reflects deviations in speech motor control.

Supplemental Material S1. Main and interaction effects of length (2-, 3-, 5-, 8-syllables) and group (control, mild ALS, severe ALS) from two-way mixed ANOVA for all articulators. Statistics were performed on original data. Statistically significant effects are in bold.

Supplemental Material S2. Bonferroni corrected pairwise comparisons to assess mean differences in STI with 95% confidence intervals. Statistics were performed on original data. Statistically significant differences are in bold.

Supplemental Material S3. Main and interaction effects of segment length (25%, 50%, 75%, 100% of an 8-syllable phrase) and group (control, Mild ALS, Severe ALS) from two-way mixed ANOVA for all articulators. Statistics were performed on original STI values. Statistically significant effects are in bold.

Supplemental Material S4. Bonferroni corrected pairwise comparisons to assess mean differences in STI values. Mean differences are provided for each articulator. Statistics were performed on original STI values. Statistically significant differences are in bold.

Teplansky, K. J., Wisler, A., Goffman, L., & Wang, J. (2023). The impact of stimulus length in tongue and lip movement pattern stability in amyotrophic lateral sclerosis. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2023_JSLHR-23-00079

Publisher Note: This article is part of the Special Issue: Select Papers From the 8th International Conference on Speech Motor Control.