More than 300,000 veterans with sensorineural hearing loss (SNHL) are fitted with VA-issued hearing aids (HAs) each year with the primary goal of improving their understanding of speech. Even older veterans without hearing loss experience a gradual decline in speech discrimination due to age-related changes in auditory function that compromise speech understanding in everyday environments. Neuroplastic reorganization within the central auditory system due to SNHL and aging contribute to these effects and compromise subjects' ability to process phonetic cues that are essential for understanding speech in noise. As a consequence, even when a HA restores high frequency signals to the cochlea in a patient with SNHL, speech understanding will remain suboptimal in the absence of rehabilitative perceptual learning.

We have developed perceptual learning paradigms that drive this rehabilitative reorganization and significantly improve speech discrimination in new HA users. We now propose to test improved training paradigms in new and experienced HA users and older subjects with normal hearing. In Exp. 1 we will evaluate baseline speech discrimination in these populations using speech-reception thresholds (SRTs) in sentences, consonant-vowel-consonant nonsense syllable tests (CVC-NST), tests of tone-pattern discrimination, and tests of auditory short-term verbal memory (ASTVM). An analysis of the correlations of these measures will provide information about basic processes underlying impaired word and sentence identification. In Exp. 2 we will investigate the effects of CVC-identification training using performance-adapted masking noise. Based on our previous results, we anticipate that training will significantly improve CVC-NST scores. We will examine the extent to which training improves SRTs, tone-pattern processing, and ASTVM. In Exp. 3 we will train subjects in a tone-pattern identification task to evaluate the extent to which non-phonetic factors (e.g., familiarity with the computerized hearing tests, placebo effects of training, improvements in auditory attention, etc.) may contribute to training benefit. In Exp. 4 we will compare the benefits of training with single-consonant syllables with the benefits of two-consonant syllable training studied in Exp. 2. Finally, in Exp. 5 we will study the benefits of CVC training using consonant-specific noise levels adjusted to compensate for intrinsic differences in the discriminability of different consonants and compare them to the benefits of global adaptive training from Exp. 2. The experiments will clarify fundamental mechanisms underlying deficits in speech discrimination and ASTVM, provide insight into the nature of training-related improvements, and elucidate the parameters needed to optimize hearing rehabilitation.

Relevance to the VA patient care mission: HAs are relatively ineffective in improving the ability of hearing-impaired subjects to understand speech in many everyday listening situations. These experiments will clarify the extent to which perceptual training can improve speech discrimination and enhance ASTVM in these conditions in new and experienced HA users and older subjects with normal hearing. Perceptual training could potentially benefit millions of veterans who wear HAs as well as older veterans with normal hearing who experience difficulties in understanding and remembering speech.