Spectral properties of fricatives in amyotrophic lateral sclerosis.

Spectral characteristics of word initial /s/ and "sh" produced by individuals with amyotrophic lateral sclerosis (ALS) and healthy controls were quantified using spectral moment analysis. Coefficients of the first four moments were used as descriptive indices of central tendency, spread of energy, shape, and peakedness. The relationship between select moment coefficients and consonant precision ratings was investigated to explore potential perceptual correlates of the acoustic measures. To examine whether spectra for ALS and healthy speakers were influenced similarly by context, first moment coefficients for three occurrences of /s/ in "some" were inspected for individual speakers. Select moment coefficients also were compared to hand-derived spectral measures for a subset of speakers. Results suggest articulatory differences in /s/ and "sh" for the present group of ALS speakers and healthy controls, as indexed by between-group differences in first moment coefficients. A linear function accounted for a significant proportion of the variance in the relationship between consonant precision ratings and the frequency difference between the first moment for /s/ and "sh". Inspection of first moment coefficients for multiple occurrences of /s/ in "some" suggests context influences the first moment in a similar manner for ALS and healthy speakers. The subanalysis comparing moment coefficients and hand-derived spectral measures revealed both similarities and differences in the manner the two measurement techniques reflect spectral shape.