Fixed-jaw effects on tongue kinematics & vowel acoustics in Amyotrophic Lateral Sclerosis
This research examined tongue movements during speech in individuals with Amyotrophic Lateral Sclerosis (ALS) and controls under two speech conditions: (1) typical (jawfree) and (2) bite block (jaw-fixed). The rationale of this study was based on previous reports that the tongue is differentially more affected than the jaw or lips by neuromuscular deterioration due to ALS; however, its impairment may be masked by compensatory jaw movements implemented to maintain speech function. To determine bite block effects on speech movements, the time to reach the maximum tongue position during the production of /i/ was measures. Further, the maximum tongue positions during the production of /i/ and the speech acoustic measures (F1/F2) of the vowel /i/ were measured. The time to the target position increased from the jaw-free to the jaw-fixed condition in all speakers with ALS. In contrast, two of three controls took less time to reach the target during the jaw-fixed than the jaw-free condition. Speakers with ALS tended to undershoot the target position to a greater extent than controls. However, relative change in vowel acoustics was greater for healthy controls than speakers with ALS. Differences in tongue performance between jaw-free and jaw-fixed conditions suggest that the tongue should be assessed in isolation of the jaw to better understand the impact of the disease on tongue speech performance. Further, little acoustic differences between experimental conditions suggest that acoustic measures are not sensitive to reflect underlying articulatory performance differences between healthy and impaired speakers with ALS.