Objective: The relationship between the acoustic measure SPL (correlate of vocal loudness) and ratings of speech intelligibility was studied in fifty-seven individuals with Parkinson’s disease (PD) following intensive voice (LSVT LOUD) or articulation (LSVT ARTIC) treatment. It was hypothesized that there would be a significant relationship between increased SPL and improved speech intelligibility.

Background: Nearly 90% of individuals with PD develop speech and voice disorders. While historically these disorders have been resistant to both medical treatments and traditional efforts at speech treatment, three randomized controlled trials (RCTs) have documented the short and long-term efficacy of intensive voice treatment (LSVT LOUD) on a range of variables including SPL (vocal loudness) [1,2,3]. Recently, greater improvements in speech intelligibility were reported following LSVT LOUD when compared to LSVT ARTIC . One explanation for these post-treatment improvements in speech intelligibility is the significant increase in SPL (vocal loudness) following LSVT LOUD.

Method: Fifty-seven individuals with PD were randomized to LSVT LOUD or LSVT ARTIC. These individuals were recorded in an IAC sound-treated booth using a head-mounted microphone. As a part of a larger protocol, they generated a monologue from which one pre and one post sentence was extracted. SPL analysis was carried out blinded using standard procedures. For speech intelligibility analysis, 117 blinded listeners orthographically transcribed the sentences for transcription accuracy (TA) and rated ease of understanding (EOU).  After ten-talker babble noise was added to the pre and post sentences, they were presented at 0dB SNL pre-treatment to the listeners who were seated individually in a sound treated booth, wearing earphones.

Results: Analysis of the relationship between pre to post changes in these variables revealed significant associations between changes in SPL (vocal loudness) and TA (transcription accuracy) (p=0.0001) and SPL and EOU (ease of understanding) (p<0.001). Reliability data for both SPL and listener ratings of intelligibility were significant.

Conclusion: These results are among the first to demonstrate a significant relationship between increased SPL (vocal loudness) and improved ratings of speech intelligibility following speech treatment for PD. NIH-NIDCD R01 DC01150

References: [1] Ramig L, Halpern A, Spielman J, Fox C, Freeman K. Speech treatment in Parkinson’s disease: Randomized controlled trial (RCT). Mov Disord 2018; 33: 1777-91. [2] Ramig L, Sapir S, Countryman S, et al. Intensive voice treatment (LSVT®) for individuals with Parkinson disease: a two-year follow-up. J Neurol Neurosurg Psychiatry 2001; 71: 493–8. [3] Ramig L, Sapir S, Fox C, Countryman S. Changes in vocal loudness following intensive voice treatment (LSVT®) in individuals with Parkinson’s disease: A comparison with untreated patients and normal age-matched controls. Mov Disord 2001; 16: 79–83.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-relationship-between-sound-pressure-level-spl-and-speech-intelligibility-in-parkinsons-disease-following-intensive-speech-treatment-lsvt-loud-and-lsvt-artic/