Reference values of maximum performance tests of speech production.

PURPOSE: Maximum performance tests examine upper limits of speech motor performance, as used by speech-language pathologists in dysarthria assessment protocols. The Radboud Dysarthria Assessment includes maximum repetition rate, maximum phonation time, fundamental frequency range and maximum phonation volume to assist in detecting pathological performance. This study aims to obtain reference values for each of these tests. METHOD: A group of 224 healthy Dutch adults aged 18-80 years performed the maximum performance tests. Age, sex, body height, smoking habit, and profession were registered. Using multivariable linear regression, a wide range of models was tested to examine the relationship between these person characteristics and speech performance. The likelihood ratio was used to test the goodness of fit to the data. RESULT: Above 60 years of age, maximum repetition rate, fundamental frequency range and maximum phonation volume were all negatively affected by age. Below 60 years, only women showed effects of age on fundamental frequency range (increase) and maximum phonation volume (decrease). Maximum phonation time was primarily related to body height (increase). CONCLUSION: This study presents reference values of four maximum performance tests for comparing the performance of dysarthric patients with non-pathological performance. Age was identified as most important factor influencing maximum speech performance.