published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

No description available.

No description available.

Existing music questionnaires have shown that postlingually deafened adult cochlear implant (CI) users generally find music to be less enjoyable following implantation. However, they did not investigate, in detail, which factors influence CI users’ music listening enjoyment, nor did they examine the approach a music training program should take. In order to obtain such information, a questionnaire, the University of Canterbury Music Listening Questionnaire (UCMLQ), was developed. The UCMLQ investigated: (i) the effect of implantation on CI users’ music listening enjoyment (determined by comparing the levels of enjoyment experienced post-implantation to prehearing loss, and just before implantation); (ii) the effect of a hearing aid in the unimplanted ear on CI users’ music perception and appreciation; (iii) the effect of timbre on music listening enjoyment whereby respondents will be asked to rate the pleasantness and naturalness of common instruments and voices, and also, give ratings on the instruments’ sound quality based on what they expect these instruments to sound to a person with normal hearing; (iv) whether respondents have a preference for a particular musical style (e.g. Country and Western, Jazz, Classical, etc); (v) whether respondents’ have a preference for, firstly, low-pitched versus high-pitched instruments/voices; secondly, music with instruments-only, voice-only, or both instruments and voice; and lastly, music with smaller number of performers versus greater number of performers; (vi) practical methods or ‘tips’ for enhancing everyday music listening enjoyment were collated; and finally, (vii) respondents were asked for their views and opinions on the content and logistics of a ‘take-home’ MTP for improving their music listening enjoyment. One-hundred postlingually deafened adult CI users, ranging in age from 18 to 88 years (mean = 62.1, SD = 17.1), completed the UCMLQ. All respondents used a Nucleus CI24 implant and the ACE speech processing strategy. Results showed that following implantation, respondents generally found music to be less enjoyable but they also preferred certain types of instruments and music: (i) low-frequency instruments over high-frequency instruments; (ii) certain instruments (e.g. the guitar) over others (e.g. brass instruments); (iii) smaller numbers of performers as opposed to larger numbers; (iv) Country and Western music as opposed to Pop/Rock, Jazz, Classical-small group, and Classical-orchestra; and (v) music with a slow rhythm/beat, and words. A comparison of the ratings given by CI and Hearing Aid (CI+HA) users and CI-only users also revealed that CI+HA users felt that they were significantly more able to follow the melody-line of musical styles, identify these styles, and they also rated musical styles to sound significantly ‘more normal’ than the CI-only users did. However, no statistically significant difference was found between the two groups’ (CI+HA users versus CI-only users) ratings for common instrumental sounds. In regards to respondents’ interest in partaking in a ‘take-home’ music training program (MTP), 54% of respondents stated that they would be interested in undertaking one. Respondents also indicated that the MTP should focus on improving their ability to recognise tunes, in particular, tunes known before implantation, and commonly-known tunes, and the MTP should offer a wide range of musical styles. In addition, training sessions should be of 30- minutes duration, 2 times per week, and the MTP should come in the form of a DVD with subtitles. Overall, this study collected information which not only helps us to better understand CI users’ appreciation of music but also could be used in the shaping and development of a future MTP.

No description available.

No description available.

No description available.

No description available.

<p>Cochlear implants (CIs) are devices that restore some level of hearing to deaf individuals. Because of their design and the impaired nature of the deafened auditory system, CIs provide listeners with limited spectral and temporal information, resulting in speech recognition that degrades more rapidly for CI listeners than for normal hearing listeners in noisy and reverberant environments (Kokkinakis and Loizou, 2011). This research project aimed to mitigate the effects of reverberation by directly manipulating the CI pulse train. A reverberation detection algorithm was initially developed to control processing when switching between the mitigation algorithm and a standard signal processing algorithm used when no mitigation is needed. Next, the benefit of removing two separate effects of reverberation was studied. Finally, two reverberation mitigation algorithms were developed. Because the two algorithms resulted in comparable performance, the effect of one algorithm on speech recognition was assessed in normal hearing (NH) and CI listeners. </p><p>Reverberation detection, which has not been thoroughly investigated in the CI literature, would provide a method to control the initiation of a reverberation mitigation algorithm. Although a mitigation algorithm would ideally remove reverberation without affecting non-reverberant signals, most noise and reverberation mitigation algorithms make errors and should only be applied when necessary. Therefore, a reverberation detection algorithm was designed to control the reverberation mitigation algorithm and thereby reduce unnecessary processing. The detection algorithm was implemented by first developing features from the frequency-time matrices that result from the standard CI speech processing algorithm. Next, using these features, a maximum a posteriori classifier was shown to successfully discriminate speech in quiet, reverberation, speech shaped noise, and white Gaussian noise with 94% accuracy.</p><p>In order to develop the mitigation algorithm that would be controlled by the reverberation detection algorithm, a unique approach to reverberation mitigation was considered. This research project hypothesized that focusing mitigation on one effect of reverberation, either self-masking (masking within an individual phoneme) or overlap-masking (masking of one phoneme by a preceding phoneme) (Bolt and MacDonald, 1949), may allow for a reverberation mitigation strategy that operates in real-time. In order to determine the feasibility of this approach, the benefit of mitigating the two effects of reverberation was assessed by comparing speech recognition scores for speech in reverberation to reverberant speech after ideal self-masking mitigation and to reverberant speech after ideal overlap-masking mitigation. Testing was completed with normal hearing listeners via an acoustic model as well as with CI listeners using their devices. Mitigating either effect was found to improve CI speech recognition in reverberant environments. These results suggested that a new, causal approach could be taken to reverberation mitigation.</p><p>Based on the success of the feasibility study, two initial overlap-masking mitigation algorithms were implemented and applied once reverberation was detected in speech stimuli. One algorithm processed a pulse train signal after CI speech processing, while the second algorithm processed the acoustic signal. Performance of the two overlap-masking mitigation algorithms was evaluated in simulation by comparing pulses that were determined to be overlap-masking with the known truth. Using the features explored in this work, performance was comparable between the two methods. Therefore, only the post-CI speech processing reverberation mitigation algorithm was implemented in a CI speech processing strategy. </p><p>An initial experiment was conducted, using NH listeners and an acoustic model designed to present the frequency and temporal information that would be available to a CI listener. Listeners were presented with speech stimuli in the presence of both mitigated and unmitigated simulated reverberant conditions, and speech recognition was found to improve after reverberation mitigation. A subsequent experiment, also using NH listeners and an acoustic model, explored the effects of recorded room impulse responses (RIRs) and added noise (speech shaped noise and multi-talker babble) on the mitigation strategy. Because reverberation mitigation did not consistently improve speech recognition in these conditions, an analysis of the fundamental differences between simulated and recorded RIRs was conducted. Finally, CI listeners were presented with simulated reverberant speech, both with and without reverberation mitigation, and the effect of the mitigation strategy on speech recognition was studied. Because the reverberation mitigation strategy did not consistently improve speech recognition, future work is required to analyze the effects of algorithm-specific parameters for CI listeners.</p> / Dissertation