Acoustic investigation of stress patterns in Parkinson's disease.

OBJECTIVES: Although reduced stress is thought to be one of the most deviant speech dimensions in hypokinetic dysarthria associated with Parkinson's disease (PD), the mechanisms of stress production in PD have not been thoroughly explored by objective methods. The aim of the present study was to quantify the effect of PD on prosodic characteristics and to describe contrastive stress patterns in parkinsonian speech. METHODS: The ability of 20 male speakers with early PD and 16 age- and gender-matched healthy controls (HCs) to signal contrastive stress was investigated. Each participant was instructed to unnaturally emphasize five key words while reading a short block of text. Acoustic analyses were based on the measurement of pitch, intensity, and duration. In addition, an innovative measurement termed the stress pattern index (SPI) was designed to mirror the effect of all distinct acoustic cues exploited during stress production. RESULTS: Although PD patients demonstrated a reduced ability to convey contrastive stress, they could still notably increase pitch, intensity, and duration to emphasize a word within a sentence. No differences were revealed between PD and HC stress productions using the measurements of pitch, intensity, duration, and intensity range. However, restricted SPI and pitch range were evident in the PD group. CONCLUSIONS: A reduced ability to express stress seems to be the distinctive pattern of hypokinetic dysarthria, even in the early stages of PD. Because PD patients were able to consciously improve their speech performance using multiple acoustic cues, the introduction of speech therapy may be rewarding.