1277 JRRD JRRD Volume 49, Number 8, 2012 Pages 1277–1292 Age-related changes in consonant and sentence processing David L. Woods, PhD; 1–2* Zoe Doss; 1 Timothy J. Herron; 1 E. William Yund, PhD 1 1 Human Cognitive Neurophysiology Laboratory, Department of Veterans Affairs Northern California Health Care Sys- tem, Martinez, CA; 2 Department of Neurology, Center for Neurosciences, and Center for Mind and Brain, University of California Davis, Sacramento, CA 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 pro- cessing ability or impairments in semantic and lexical process- ing 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 sub- jects with normal hearing, particularly for hard-to-identify con- sonants, 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 exam- ined 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 suc- cess of audiological rehabilitation in older subjects with hearing impairment. Key words: aging, audiometry, auditory cortex, consonant, hearing loss, learning, nonsense syllables, speech comprehen- sion, 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 lex- ical and semantic impairments that are most clearly revealed in sentence testing [9]. A primary goal of audiological rehabilitation of older subjects with hearing impairment (OHI) is to restore speech understanding to normal levels with hearing aids Abbreviations: ANOVA = analysis of variance, B = baseline, CaST = California Syllable Test, CVC = consonant-vowel- consonant, HINT = Hearing in Noise Test, HPTA = high- frequency pure-tone average, LPTA = low-frequency pure-tone average, MRI = magnetic resonance imaging, NS = not signifi- cant, OHI = older (subjects with) hearing impairment, ONH = older (subjects with) normal hearing, P/I = performance/inten- sity, QuickSIN = Quick Speech in Noise Test, SD = standard deviation, SeRT = sentence reception threshold, SNHL = sen- sorineural hearing loss, SNR = signal-to-noise ratio, SPL = sound pressure level, YNH = younger (subjects with) normal hearing. * Address all correspondence to David L. Woods, PhD; Neu- rology Service (127E), Department of Veterans Affairs Northern California Health Care System, 150 Muir Rd, Martinez, CA 95553; 925-372-2571; fax: 925-228-5738. Email: dlwoods@ucdavis.edu http://dx.doi.org/10.1682/JRRD.2011.08.0150