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Thesis: Investigation into the Enhancement of Voice Perception

Ceha, J. M. (2016) Thesis: Investigation into the Enhancement of Voice Perception. Master's Thesis / Essay, Human-Machine Communication.

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Cochlear implants (CI) restore hearing in individuals with profound to severe hearing loss via electric stimulation of the auditory nerve. Unfortunately, modern CIs suffer from degraded fine spectrotemporal resolution. As a result, CI users have difficulty perceiving important voice characteristics for higher level speech perception, specifically, the fundamental frequency (F0) and the vocal-tract length (VTL). Research has shown that CI users with residual low-frequency hearing greatly benefit from a hearing aid in the non-implanted ear. This is known as bimodal hearing and provides electric stimulation via the CI, in addition to acoustic amplification for the low-frequency sounds, that an individual may still hear naturally. The focus of this thesis was two-fold. First, neurofeedback training was developed, aimed at improving VTL perception using CI simulations The results indicated a necessity for further research into event-related potentials, specifically the P300 waveform, elicited by non-word, vocoded speech stimuli. Second, a study was conducted which investigated how the comparison and integration of the different sound signals in bimodal hearing impacts perception of the F0 and VTL. Normal hearing listeners heard vocoded CI speech simulations in one ear and low-pass filtered (LPF) speech in the other. Three listening conditions (vocoded CI-alone, LPF-alone, and bimodal) were tested, across varying degrees of spectral degradation, implemented through the vocoder, and with two different LPFs applied to the acoustic signal: 150 and 300 Hz. The results showed a significant improvement in F0 perception in the bimodal conditions compared to the vocoded CI-alone conditions, with no increase in improvement above the 150 Hz LPF. Additionally, there was no impact of spectral degradation on the improvement. The results provide evidence for the role of the F0, present in the acoustic signal, in supporting enhanced speech recognition performance in bimodal hearing. Furthermore, it suggests that amplification of residual low-frequency hearing as low as 150 Hz can provide bimodal benefit in quiet, and that overlapping frequency maps between the CI and hearing aid does not cause interference of the signals.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Human-Machine Communication
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:24
Last Modified: 15 Feb 2018 08:24

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