Improving hearing ability in challenging conditions

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Abstract

Although speech recognition using hearing aids and cochlear implants has improved significantly recently, most people with hearing impairment still have difficulty understanding speech in noisy environments. Improving the ability of the brain to learn how to make full use of prosthetic devices is as important as developments in the technology. Auditory perceptual training helps people to be more sensitive to target sounds. Therefore, auditory training programmes have the potential to optimise the performance of hearingimpaired users and help them get more benefit from their prosthetic devices. Better understanding of how and when auditory perceptual training generalises with normal hearing people may help in devising better training for people with hearing impairment. However, in literature, researchers have mainly focused on changing the target stimuli using amplitude modulated sounds or speech stimuli. Fewer researchers have explored the auditory learning and generalization effect of changing the background noise. It is not clear whether training generalizes to other types of noise, and in particular real-world environmental noises.

A novel element of this study is that it focuses on auditory training of people to pick up the target stimuli by changing the background noise. This project was divided into four stages. The first stage of this work looked at basic detection thresholds for amplitude modulation (AM) in sound stimuli, and found that training with AM-detection did not generalize to AM-rate discrimination, regardless of the modulation depths. For the second stage, two nonsense stimuli (Vowel Consonant Vowel VCV) training studies were carried out to explore auditory perceptual learning patterns with nonsense syllables across fixed and random background noise. It was motivated by visual research which showed that people can improve their detection performance by learning to ignore constant visual noise and that this skill transfers to new, random visual noise. Results showed that learning with random noise produced better identification performance than with fixed noise. There was no generalization from fixed noise training to random noise environments. These results were in contrast to the visual learning studies. Followed by the second stage, a short single session VCV study was conducted to investigate whether nonsense syllable adaption to fixed noise was different to random noise. Results showed that listeners’ VCV identification was similar for fixed and random babble noise conditions. This was different from stage two that showed better nonsense recognition with random noise training than with fixed noise training. It is suggested that test method differences (multi-sessions vs single session) lead to performance differences between fixed and random noise conditions. The final stage of this work was to explore whether any learning effect from training with speech in random babble noise generalized to other environmental noises, such as car and rain. Results demonstrated that speech in babble noise training generalized to car and rain noise conditions, and part of the learning effect from speech in babble noise was sustained after several weeks.

This project investigated auditory perceptual learning performance of normal hearing people using AM stimuli, nonsense speech, and speech with various types of background noise (babble, car, rain). The learning outcomes provide important evidence for the use of background noises (fixed noise, random noise, and real-world environmental noises) in auditory perceptual training programmes, which can help to build up clinical guidelines for training people with hearing impairment to improve their hearing in challenging conditions.

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