The effect of auditory memory load on intensity resolution in individuals with Parkinson's disease
Richardson, Kelly C.
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Purpose: The purpose of the current study was to investigate the effect of auditory memory load on intensity resolution in individuals with Parkinson's disease (PD) as compared to two groups of listeners without PD. Methods: Nineteen individuals with Parkinson's disease, ten healthy age- and hearing-matched adults, and ten healthy young adults were studied. All listeners participated in two intensity discrimination tasks differing in auditory memory load; a lower memory load, 4IAX task and a higher memory load, ABX task. Intensity discrimination performance was assessed using a bias-free measurement of signal detectability known as d' (d-prime). Listeners further participated in a continuous loudness scaling task where they were instructed to rate the loudness level of each signal intensity using a computerized 150mm visual analogue scale. Results: Group discrimination functions indicated significantly lower intensity discrimination sensitivity (d') across tasks for the individuals with PD, as compared to the older and younger controls. No significant effect of aging on intensity discrimination was observed for either task. All three listeners groups demonstrated significantly lower intensity discrimination sensitivity for the higher auditory memory load, ABX task, compared to the lower auditory memory load, 4IAX task. Furthermore, a significant effect of aging was identified for the loudness scaling condition. The younger controls were found to rate most stimuli along the continuum as significantly louder than the older controls and the individuals with PD. Conclusions: The persons with PD showed evidence of impaired auditory perception for intensity information, as compared to the older and younger controls. The significant effect of aging on loudness perception may indicate peripheral and/or central auditory involvement.