A Phonetic Complexity-Based Approach for Intelligibility and Articulatory Precision Testing: A Preliminary Study on Talkers With Amyotrophic Lateral Sclerosis.

Purpose: This study describes a phonetic complexity-based approach for speech intelligibility and articulatory precision testing using preliminary data from talkers with amyotrophic lateral sclerosis. Method: Eight talkers with amyotrophic lateral sclerosis and 8 healthy controls produced a list of 16 low and high complexity words. Sixty-four listeners judged the samples for intelligibility, and 2 trained listeners completed phoneme-level analysis to determine articulatory precision. To estimate percent intelligibility, listeners orthographically transcribed each word, and the transcriptions were scored as being either accurate or inaccurate. Percent articulatory precision was calculated based on the experienced listeners' judgments of phoneme distortions, deletions, additions, and/or substitutions for each word. Articulation errors were weighted based on the perceived impact on intelligibility to determine word-level precision.
Results: Between-groups differences in word intelligibility and articulatory precision were significant at lower levels of phonetic complexity as dysarthria severity increased. Specifically, more severely impaired talkers showed significant reductions in word intelligibility and precision at both complexity levels, whereas those with milder speech impairments displayed intelligibility reductions only for more complex words. Articulatory precision was less sensitive to mild dysarthria compared to speech intelligibility for the proposed complexity-based approach. Conclusions: Considering phonetic complexity for dysarthria tests could result in more sensitive assessments for detecting and monitoring dysarthria progression.