Age-related changes in consonant and sentence processing.

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.