Phonetic complexity, speech accuracy and intelligibility assessment of Italian dysarthric speech

Intelligibility is the degree to which the speech of a person may be understood by a listener, and is related to functional limitation and disability. In protocols for the clinical assessment of dysarthria, intelligibility checks are included, as well as evaluations of speech accuracy, which is more directly related to the disease severity. However, both evaluations are usually based on subjective ratings. Aim of this work is checking the correlation between intelligibility judgements, subjectively assigned as it may be the case in clinical procedures, and acoustic measures related to linguistically contrasting units. Two novelties characterize this work: a) acoustic measurements considered in the paper relate to both segments (vowel and consonants) and prosodic-intonational phonological events (e.g., pitch accents), that is linguistically relevant speech units; b) contexts of increasing phonetic-phonological complexity are considered, in order for the phonetic characteristics to challenge production accuracy, possibly affecting the realization of phonological features and intelligibility. Increasing complexity is expected to challenge intelligibility indeed and to have an impact on the correlation between intelligibility rates and acoustic measures. Results are preliminary, but confirm both 1) the correlation between acoustic measures of linguistically relevant events and speech intelligibility, as for both the segmental and the prosodic-intonational level, and 2) the role of increasing phonetic-phonological complexity in enhancing the above mentioned correlation.