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Abbreviations: ANOVA = analysis of variance, B = baseline, CaST = California Syllable Test, CVC = consonant-vowelconsonant, HINT = Hearing in Noise Test, HPTA = highfrequency pure-tone average, LPTA = low-frequency pure-tone average, MRI = magnetic resonance imaging, NS = not significant, OHI = older (subjects with) hearing impairment, ONH = older (subjects with) normal hearing, P/I = performance/intensity, QuickSIN = Quick Speech in Noise Test, SD = standard deviation, SeRT = sentence reception threshold, SNHL = sensorineural hearing loss, SNR = signal-to-noise ratio, SPL = sound pressure level, YNH = younger (subjects with) normal hearing.
Abstract-Speech understanding in noise declines with age, even in older subjects with normal hearing (ONH). These age-related declines could reflect reductions in phonological processing ability or impairments in semantic and lexical processing required for sentence understanding. In experiment 1, we used the California Syllable Test (CaST) to examine age-related changes in the ability of subjects to identify consonants in consonant-vowel-consonant syllables in noise. ONH subjects showed impaired performance in comparison with younger subjects with normal hearing, particularly for hard-to-identify consonants, but otherwise showed similar influences of consonant position, lexicality, and vowel nuclei. Regression analyses showed that CaST performance was independently affected by both age and audiometric thresholds. In experiment 2, we examined sentence reception thresholds (SeRTs) using the Quick Speech in Noise Test and Hearing in Noise Test. No significant age-related changes in SeRTs were observed for either test. SeRT preservation in ONH subjects appeared to reflect the age-resistant ability to identify easy consonants in noise as well as intact top-down contextual and lexical processing. These results establish benchmark values that can be used to evaluate the success of audiological rehabilitation in older subjects with hearing impairment.
Key words: aging, audiometry, auditory cortex, consonant, hearing loss, learning, nonsense syllables, speech comprehension, threshold, vowel.
INTRODUCTION: EXPERIMENT 1
Although it is well established that aging impairs speech comprehension in noise in older subjects [1-4], the relative contribution of peripheral and central changes to presbycusic deterioration remains an area of active investigation. Some researchers hypothesize that age-related changes in speech comprehension primarily reflect deterioration in cochlear function [5], whereas others ascribe an important role to deficits in central auditory processing [6-7]. Central deficits may reflect impaired phonological processing [8] or higher-level...