Parameterization of articulatory pattern in speakers with ALS

A combination of parallel factor analysis (PARAFAC) and principal component analysis (PCA) was used to parameterize the articulatory pattern of tongue, jaw and lip movements in 8 English vowels produced by 7 subjects with amyotrophic lateral sclerosis (ALS). A two-factor PARAFAC model derived an overall articulatory pattern represented by two basic modes dominated by tongue raising and advancement, respectively. The relation between the two articulatory modes and the acoustic formants (F1, F2) followed a simple one-to-one linear mapping. The PCA on the residuals of the PARAFAC model showed various individualized articulatory features superimposed on the overall pattern. These articulatory features contributed in a systematic way to the acoustic deviation across different subjects. The parameterization approach (1) provided a simple and generalizable way to explore the underlying articulatory mechanism of speech decline in ALS and (2) accounted for the articulatory features across affected individuals. With further development of the approach and a comparison with the articulatory pattern for healthy subjects, it is possible to derive a set of quantitative articulatory indicators of speech impairment in ALS.