Consonant intelligibility in individuals with Parkinson's disease in noise: Pre-specified secondary outcome variables from a randomized control trial (RCT) comparing two intensive speech treatments (LSVT LOUD vs. LSVT ARTIC)

The majority of people with Parkinson's disease (PD) experience changes in speech production, most notably reduced vocal volume and imprecise articulation, that limit speech intelligibility and may contribute to significant declines in quality of life. We previously conducted a randomized control trial comparing two intensive treatments, voice (LSVT LOUD) or articulation (LSVT ARTIC) to assess single word intelligibility in the presence of background noise (babble and mall). Participants (64 PD and 20 Healthy) read words from the diagnostic rhyme test (DRT), an ANSI Standard for measuring intelligibility of speech, before and after one month (treatment or no treatment). Teams of trained listeners blindly rated the data. Previously we found that single word intelligibility in the presence of both noise conditions improved in PD participants who had LSVT LOUD compared to the groups that had LSVT ARTIC or no treatment. The current study analyzed the distinctive features (Compactness, Graveness, Sustention, Sibilation, Nasality, Voicing), of the initial consonants of words in the DRT test to determine what in particular is contributing to the differences in word intelligibility that we previously identified. The distinctive features of the DRT assess the valving nature of consonant production. Intensive treatment targeting vocal loudness (LSVT LOUD) had a greater positive effect on consonant intelligibility than treatment targeting articulation (LSVT ARTIC) for all distinctive features in background Babble noise and for 5/6 distinctive features in background Mall noise. Due to the definition of the distinctive features, we can conclude that the intelligibility gains seen following LSVT LOUD treatment are due to improved vocal tract valving.