Purpose: Reduced intensity is a hallmark of speech production in Parkinson's disease (PD). Previous work has examined the perception of intensity in PD to explain these speech deficits. This study reports loudness ratings of pure tones by individuals with PD and controls, all with normal thesholds for older adults.
Method: Twenty individuals with PD and 23 age- and sex-matched controls rated the loudness of pure tones from 1 (very soft) to 7 (uncomfortably loud). Tones at 500, 750, 1000, 2000, and 4000 Hz were presented from 35 to 80 dB HL (or until a rating of 7 was given). A mixed-model analysis of variance was performed on ratings to assess the effects of group, frequency, sound intensity, and ear. Loudness growth slopes were determined for each participant and analyzed by group.
Results: The mean loudness growth slopes of the control and PD groups did not significantly differ.
Conclusions: No difference was found in loudness growth slopes in response to externally generated tones in PD. This is in contrast with the findings of previous studies of self-generated speech and externally presented speech. The underlying causes for impaired perception and production of loudness in PD require further investigation.