Differential spectral characteristics of the Spanish fricative /s/ in the articulation of individuals with dysarthria and apraxia of speech.

PURPOSE: This study examines whether there are differences in the speech of speakers with dysarthria, speakers with apraxia and healthy speakers in spectral acoustic measures during production of the central-peninsular Spanish alveolar sibilant fricative /s/. METHOD: To this end, production of the sibilant was analyzed in 20 subjects with dysarthria, 8 with apraxia of speech and 28 healthy speakers. Participants produced 12 sV(C) words. The variables compared across groups were the fricative's spectral amplitude difference (AmpD) and spectral moments in the temporal midpoint of fricative execution. RESULTS: The results indicate that individuals with dysarthria can be distinguished from healthy speakers in terms of the spectral characteristics AmpD, standard deviation (SD), center of gravity (CoG) and skewness, the last two in context with unrounded vowel, while no differences in kurtosis were detected. Participants with AoS group differ significantly from healthy speaker group in AmpD, SD and CoG and Kurtosis, the first one followed unrounded vowel and the latter two followed by rounded vowels. In addition, speakers with apraxia of speech group returned significant differences with respect to speakers with dysarthria group in AmpD, CoG and skewness. CONCLUSIONS: The differences found between the groups in the measures studied as a function of the type of vowel context could provide insights into the distinctive manifestations of motor speech disorders, contributing to the differential diagnosis between apraxia and dysarthria in motor control processes.

Temporal acoustic properties of the sibilant fricative /s/ for the differential diagnosis of dysarthria and apraxia of speech in Spanish speakers.

Dysarthria and Apraxia of Speech (AoS) are motor speech disorders in which neurological lesions differentially affect motor control, possibly leading to noticeable differences in articulation and consequently sound production. Among the sounds requiring greater motor capacity because of its articulatory complexity is the voiceless alveolar sibilant fricative /s/. The aim of this study was to identify acoustic variables able to distinguish between dysarthria and AoS, and between these disorders and normal speech in Spanish speakers. The production of this fricative was acoustically examined in 28 individuals with motor neurological disorders (20 with dysarthria, 8 with AoS) and in 28 neurologically healthy persons. Participants repeated 12 monosyllabic words containing the fricative plus one of the five Spanish vowels. The variables measured were absolute durations of the fricative, vowel, and fricative+vowel sequence, along with the vowel-to-fricative duration ratio. Findings indicate that duration of the fricative can distinguish between controls and speakers with dysarthria, but not between controls and speakers with AoS. Measures related to vowel duration served to distinguish between speakers with dysarthria and speakers with AoS and between each of them and controls. Further, speakers with dysarthria and those with AoS differed from each other and from controls in terms of articulatory variability; speakers with dysarthria showing most variability. In the latter participants, articulatory variability was higher for unrounded segments, vowels and fricatives, while in speakers with AoS this variability was higher for rounded segments. These observations are discussed within a framework of motor control models.