Perceptual training improves syllable identification in new and experienced hearing aid users.

Abstract--We assessed the effects of perceptual training of syllable identification in noise on nonsense syllable test (NST) performance of new (Experiment 1) and experienced (Experiment 2) hearing aid (HA) users with sensorineural hearing loss. In Experiment 1, new HA users were randomly assigned to either immediate training (IT) or delayed training (DT) groups. IT subjects underwent 8 weeks of at-home syllable identification training and in-laboratory testing, whereas DT subjects underwent identical in-laboratory testing without training. Training produced large improvements in syllable identification in IT subjects, whereas spontaneous improvement was minimal in DT subjects. DT subjects then underwent training and showed performance improvements comparable with those of the IT group. Training-related improvement in NST scores significantly exceeded improvements due to amplification. In Experiment 2, experienced HA users received identical training and testing procedures as users in Experiment 1. The experienced users also showed significant training benefit. Training-related improvements generalized to untrained voices and were maintained on retention tests. Perceptual training appears to be a promising tool for improving speech perception in new and experienced HA users. Key words: auditory, hearing aid, hearing loss, learning, masking noise, nonsense syllables, perception, perceptual training, personal computer, phonemes, presbycusis, rehabilitation, speech. INTRODUCTION Progressive high-frequency sensorineural hearing loss (SNHL) alters auditory processing at multiple levels of the auditory system. Most obviously, it alters cochlear function and deprives listeners of high-frequency speech cues that are critical in discriminating consonants [1]. In addition, gradual high-frequency SNHL results in a widespread reorganization of central auditory connections, diminishing high-frequency inputs and enhancing connections from nearby zones with intact cochlear function [2]. Phoneme processing strategies are correspondingly altered, with hearing-impaired subjects depending more on phonetic cues conveyed by low frequencies [3-6]. For example, hearing-impaired subjects rely disproportionately on vowel duration to discriminate voiced and voiceless fricative pairs such as /v/-/f/ and /z/-/s/ [4]. While hearing aids (HAs) can partially compensate for cochlear deficits by amplifying high-frequency sounds, long-standing peripheral hearing loss will also produce neuroplastic alterations within the central auditory system, including changes in synaptic connections and dendritic arborization [7]. While the newly amplified auditory inputs provided by HAs may enhance functional neuroplasticity [8], abnormal synaptic connections will not instantly renormalize. Normalization may be reflected in the gradual perceptual changes occurring during acclimatization [9-11]. However, acclimatization effects are generally small in magnitude and inconsistently obtained [12-15]. This minimal acclimatization benefit suggests that the neuroplastic changes needed to normalize auditory perception often may not occur. In the current study, we investigated the capability of adaptive perceptual training to force reorganization and consequent perceptual improvement in a high-level auditory task: syllable identification. Cortical Plasticity and Perceptual Learning Research over the last decade has revealed extensive neuroplasticity in the auditory system that optimizes neuronal responses to the behaviorally relevant acoustic features present in the environment [16-18]. Changes in cortical organization occur reliably following both selective stimulation and deprivation. For example, explicit exposure to particular sound frequencies can enhance the number of cortical neurons driven by those stimuli and alter neuronal tuning properties and response latencies to favor behaviorally relevant sounds [19]. Environmental enrichment can also sharpen neuronal tuning curves in auditory cortex [20], while noisy environments impair the development of normal tuning [21]. …