The relationship between the intensity and loudness of self-generated (autophonic) speech remains invariant despite changes in auditory feedback, indicating that non-auditory processes contribute to this form of perception. The aim of the current study was to determine if the speech perception deficit associated with Parkinson's disease may be linked to deficits in such processes. Loudness magnitude estimates were obtained from parkinsonian and non-parkinsonian subjects across four separate conditions: self-produced speech under normal, perturbed, and masked auditory feedback, as well as auditory presentation of pre-recorded speech (passive listening). Slopes and intercepts of loudness curves were compared across groups and conditions. A significant difference in slope was found between autophonic and passive-listening conditions for both groups. Unlike control subjects, parkinsonian subjects' magnitude estimates under auditory masking increased in variability and did not show as strong a shift in intercept values. These results suggest that individuals with Parkinson's disease rely on auditory feedback to compensate for underlying deficits in sensorimotor integration important in establishing and regulating autophonic loudness.
We would like to thank William Hula for insightful suggestions in putting together this experiment. This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the National Institutes of Health (Grant No. NIDCD-R01DC012502).
I. INTRODUCTION II. METHODS A. Participants B. Procedure C. Instrumentation III. DATA ANALYSIS A. Intra-subject correlations B. Curve fitting IV. RESULTS V. DISCUSSION