Effects of aging on the fine structure of the 2f1-f2 acoustic distortion product.
The fine structures of 2f1-f2 acoustic distortion products (ADP) were measured in four groups of human subjects: (1) young with normal hearing, (2) aged with normal or near-normal hearing, (3) aged subjects with more severe hearing loss above 2000 Hz, and (4) young with hearing similar to those of the normal- or near-normal-hearing aged group. The purpose of this study was to investigate how ADP fine structure changes with age and hearing loss. Results show that the fine structure is observable whenever the ADP is measurable, and its sharpness, defined as the peak-to-peak frequency distance, is independent of age hearing loss, and longitudinal amplitude change. There is a large variance in ADP peak amplitudes in aged subjects with or without hearing loss as compared to young normal hearing subjects, the aged group generally having lower peak amplitudes than those of the young group. According to an ANOVA analysis with absolute threshold as covariate, the null hypothesis stating that there is no aging effect on the ADP peak responses cannot be ruled out, a conclusion similar to that made by Stover and Norton [J. Acoust. Soc. Am. 94, 2670-2681 (1993)]. On the other hand, threshold changes cannot explain all the differences in ADP amplitude. It is clear that the relationship between ADP amplitudes and behavioral thresholds can differ between young and aged populations. At primary levels of 50 dB SPL, almost normal ADP magnitudes are often found in aged subjects even when associated with a 35-dB hearing loss, whereas for young subjects ADPs typically were not measurable when associated with the pure-tone thresholds of 20 dB HL or higher. This dichotomy may be explained by the different etiologies of cochlear pathologies predominant in the two groups.
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Department of Otolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425-2242.
Schmiedt
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D000162:Acoustics; D000328:Adult; D000367:Age Factors; D000375:Aging; D001301:Audiometry, Pure-Tone; D005260:Female; D006309:Hearing / Q000502:physiology; D006311:Hearing Disorders / Q000175:diagnosis; D006801:Humans; D008297:Male; D010469:Perceptual Distortion