One
of the key features of the hypokinetic dysarthria associated with Parkinson
disease is dysprosody. While there has been ample research into the global
characterization of speech in Parkinson disease, little is known about how
people with Parkinson disease mark lexical stress. This study aimed to determine
how people with Parkinson disease modulate pitch, intensity, duration, and
vowel space to differentiate between two common lexical stress patterns in
English: trochees (strong-weak pattern) and iambs (weak-strong pattern), in two
syllable words. Twelve participants with mild to moderate idiopathic Parkinson
disease and twelve age- and sex-matched controls completed a series of speech
tasks designed to elicit token words of interest in prosodically-relevant speech
tasks (picture identification (in isolation and lists) and giving directions
(spontaneous speech). Results revealed that people with Parkinson disease produced
a higher overall pitch and a smaller vowel space as compared to controls,
though most lexical marking features were not significantly different. Importantly,
the elicitation task had a significant effect on most dependent measures. Although
lexical stress is not significantly impacted by Parkinson disease, we recommend
that future research and clinical practice focus more on the use of spontaneous
speech tasks rather than isolated words or lists of words due to the
differences in the marking of lexical stress in the latter tasks, making them
less useful as ecologically-valid assessments of prosody in everyday
communication.