Compression hearing aids are the most common remedy for individuals with hearing loss. User benefit depends upon the ability of compression hearing aids to provide the acoustic cues necessary for speech recognition. The detection of amplitude modulations (variations in intensity) and gaps (silent intervals) are essential for speech recognition. Compared to linear amplification, compression might degrade amplitude modulation detection thresholds but improve gap detection thresholds. The recognition of consonant place cues depends upon the ability to detect amplitude modulations in speech whereas the ability to detect consonant manner cues depends upon the ability to detect gaps in speech. In order to improve the outcomes of hearing aid users, it is critical that we determine how compression compared to linear amplification affects amplitude modulation detection thresholds, gap detection thresholds, and speech recognition. Understanding those relationships can lead to improved hearing aid fitting protocols, improved signal processing for hearing aids, and improved evidence based clinical guidelines. Surprisingly, the ability to detect gaps or amplitude modulations has not been evaluated for fitting hearing aids.
The first aim i s to measure the ability of hearing aid users to detect amplitude modulations and gaps while listening through a hearing aid. The subjects will be tested under two different hearing aid conditions. The first condition is linear amplification, which should not distort modulation or gap cues. The second condition is compression, which is expected to reduce modulation cues but improve gap cues. Additionally, the project will evaluate whether a broadband noise or narrowband noise carrier better predicts speech recognition. Different carrier signals, representing the carrier (vocal folds) and the modulator (vocal tract) in speech, will be used.
The second aim i s to compare psychoacoustic thresholds with speech recognition. Speech recognition will be measured with voiceless consonants because subjects with hearing loss have difficulty recognizing voiceless consonants. In order to focus on the temporal cues of interest, the speech signal will be vocoded to minimize spectral cues. Differences in amplitude modulation, gap detection thresholds, consonant place identification, and consonant manner identification between compression and linear amplification will be calculated for each subject. The differences in amplitude modulation thresholds will be compared to differences in consonant place identification. The differences in gap detection thresholds will be compared to differences in consonant manner identification. The goal is to lay the groundwork for developing hearing aid fitting protocols based on modulation and gap detection thresholds.
Hearing aid users continue to recognize less speech than normal hearing listeners and this might be because it is unclear how hearing aids alter important speech cues. This study will measure the ability of hearing aid users to detect acoustic cues essential for speech recognition and then relate those results to speech recognition. This may lead to improved speech recognition for hearing aid users.
|Brennan, Marc A; Gallun, Frederick J; Souza, Pamela E et al. (2013) Temporal resolution with a prescriptive fitting formula. Am J Audiol 22:216-25|