In the period immediately following the implantation of a cochlear implant electrode array within the cochlear environment, the power required to stimulate the auditory nerve at preset current levels increases. This rise is due to increases in electrode impedance which in turn is suggested to be a result of tissue growth around the electrode array. The foreign body response initiated by the immune system encapsulates the array in a matrix of fibrous tissue, separating the electrode array from the rest of the body. A second change in electrode impedance occurs with the onset of electrical stimulation. A transitory reduction in impedance has been recorded in animals and humans after stimulation of electrodes. Impedance returns to pre-stimulation levels following the cessation of stimulation. It was suggested that these changes in impedance with stimulation were also related to the tissue growth around the electrode array. A more thorough understanding of the interface was required to ascertain these concepts.

In the United States, permanent hearing loss affects approximately 3 newborns in 1,000 making it the most common birth defect. Current widespread use of universal newborn hearing screening has resulted in an average age of identification of hearing loss of 2-3 months. As the population of children who are identified early in life and fitted with cochlear implants (CI) grows, speech-language pathologists (SLPs) are likely encounter clients from this population. However, the majority of SLPs are not educated as to the various modes of communication that can be used with children with CI as they learn spoken language. The focus of this review is to provide SLPs with an evidence-based resource to guide their decision-making regarding appropriate communication mode for children with CI. / text

In the period immediately following the implantation of a cochlear implant electrode array within the cochlear environment, the power required to stimulate the auditory nerve at preset current levels increases. This rise is due to increases in electrode impedance which in turn is suggested to be a result of tissue growth around the electrode array. The foreign body response initiated by the immune system encapsulates the array in a matrix of fibrous tissue, separating the electrode array from the rest of the body. A second change in electrode impedance occurs with the onset of electrical stimulation. A transitory reduction in impedance has been recorded in animals and humans after stimulation of electrodes. Impedance returns to pre-stimulation levels following the cessation of stimulation. It was suggested that these changes in impedance with stimulation were also related to the tissue growth around the electrode array. A more thorough understanding of the interface was required to ascertain these concepts.

Telephones are an integral part of everyday life in today's society. It is well known that hearing impaired people have difficulty understanding speech on the telephone. The ability to use the telephone is commonly reported as one of the many benefits of cochlear implantation. Assessment for a cochlear implant (CI) includes a variety of aspects related to communication and hearing ability. Included in the case history, mention is made whether the person can use the telephone. The purpose of the present study was firstly to identify if the inability to use the telephone could be used a predictor for suitability for a cochlear implant. It was also purposed to determine if telephone ability could be assessed by self-reported measures. The participants were 13 severe to profoundly hearing impaired people who had previously undergone candidacy assessment for a cochlear implant. Each participant was evaluated on their use and understanding of speech on the telephone. Participants were separated into two groups: those who were candidates for a cochlear implant and those who were not. Speech perception testing was evaluated using a recording of CUNY sentences on the telephone. Results indicated that cochlear implant candidates correctly perceived a significantly lower number of words on the telephone than non-candidates. Use of the telephone was evaluated using a 51-item questionnaire. Results indicated that there was no significant difference in self-reported use of the telephone between cochlear implant candidates and non-candidates. The differences in speech perception understanding on the telephone were most likely due to the overall better hearing levels of the non-candidates. The clinical implications of the present study are considered.

Hearing loss is a common impairment or disability for human beings, and is impacting an increasing amount of people, augmented by the growing aging population around the globe. Cochlear implantation, as one of the most effective ways to restore hearing, can only applied to profoundly deaf patients at the moment. In order to expand the group of people who can benefit from cochlear implantation to those with less severe hearing loss, endeavours need to be made to best preserve residual hearing and minimise trauma induced during cochlear implantation surgery. In this thesis, the disturbance induced in the cochlea, i.e. the acoustic and mechanical energy transmitted into the cochlea, during cochleostomy drilling is studied - as well as establishing a comparison between a manually guided conventional technique and a manually supported tissue guided robotic drilling technique. The results show that by changing surgical techniques and how they are applied can have a significant impact on levels of disturbance induced - robotic-aided approach induced lower level of equivalent SPL for up to 86% of the time and can be as much as 39 dB lower than that generated by conventional surgical drilling. This work is timely because trauma is an important consideration to clinicians and health care providers. Cochleostomy is one of the major and most disruptive surgical process during cochlear implantation. With the increasing amount of cochlear implant electrode array designs that are shorter and less intrusive, and the increasing demand of electric-acoustic stimulation via cochlear implant to better resemble the human auditory system, the approach to reduce disruption during cochleostomy drilling is highly relevant to the progression in the hearing care industry and the benefits of the growing hearing impairment community.

Many cochlear implant (CI) recipients report the sound quality of their devices to be poor, for listening to music. The latest MED-EL speech processing strategy, Fine Structure Processing (FSP), aims to improve sound quality by encoding some of the low-frequency fine structure (FS) information. The goals of this study were twofold. The first was to develop a music quality rating test battery (MQRTB) for the New Zealand and Australian populations using commercially available songs. The second was to pilot test the MQRTB in a study comparing the MED-EL speech processing strategies FSP and High Definition Continuous Interleaved Sampling (HDCIS) for music appreciation. The research questions for the second part of this study were: (1) Does familiarity with a speech processing strategy affect musical quality ratings?; (2) Do CI recipients notice a significant difference between FSP and HDCIS when listening to music and if so, what aspects of the sound are different?; (3) Does song familiarity affect the quality ratings of music in CI recipients?; (4) Does music genre affect the quality ratings of music in CI recipients? The MQRTB used visual analogue scales for the attributes of pleasantness, naturalness, richness, fullness, sharpness, and roughness while listening to a home stereo. The scales were displayed on a computer touchscreen with the stimuli being presented via a home stereo system. There were ten songs in the MQRTB; a familiar and obscure song from each of the following genres: classical, modern, country and western, and common (such as a national anthem or iconic melody) genres, as well as two of the participant’s favourite songs. Five post-lingually deafened MED-EL SonataTI100 or PulsarCI100 CI recipients using the FSP strategy took part in the FSP versus HDCIS comparison study. Each participant spent three weeks acclimatising to either FSP or HDCIS before completing speech perception testing and the MQRTB task. Following this the participants were switched to the other speech processing strategy to acclimatise to for a further three weeks before re-assessment with the second strategy. At the conclusion of the study, the participants’ speech processors were returned to the pre-study settings. The results of the study showed an effect of acclimatisation on music quality ratings; when the participants were acclimatised to FSP, the group tended to prefer FSP; however, when acclimatised to HDCIS, the participants did not prefer HDCIS. As a group they rated FSP to sound closer to ‘what they would like music to sound like’ than HDCIS, and that HDCIS sounded significantly sharper and rougher than FSP. This suggested that music appreciation was better with FSP, but participants needed to be acclimatised to the strategy first. No effect of familiarity or genre was observed in the averaged group data, however, effects for some individuals were noted. Overall it would appear that FSP may improve music sound quality for some MED-EL CI recipients, however, it does not solve this issue. The MQRTB was also shown to be an effective tool to assess some aspects of music sound quality.

Telephones are an integral part of everyday life in today's society. It is well known that hearing impaired people have difficulty understanding speech on the telephone. The ability to use the telephone is commonly reported as one of the many benefits of cochlear implantation. Assessment for a cochlear implant (CI) includes a variety of aspects related to communication and hearing ability. Included in the case history, mention is made whether the person can use the telephone. The purpose of the present study was firstly to identify if the inability to use the telephone could be used a predictor for suitability for a cochlear implant. It was also purposed to determine if telephone ability could be assessed by self-reported measures. The participants were 13 severe to profoundly hearing impaired people who had previously undergone candidacy assessment for a cochlear implant. Each participant was evaluated on their use and understanding of speech on the telephone. Participants were separated into two groups: those who were candidates for a cochlear implant and those who were not. Speech perception testing was evaluated using a recording of CUNY sentences on the telephone. Results indicated that cochlear implant candidates correctly perceived a significantly lower number of words on the telephone than non-candidates. Use of the telephone was evaluated using a 51-item questionnaire. Results indicated that there was no significant difference in self-reported use of the telephone between cochlear implant candidates and non-candidates. The differences in speech perception understanding on the telephone were most likely due to the overall better hearing levels of the non-candidates. The clinical implications of the present study are considered.

Cochlear implants (CIs) are prosthetic devices used to partially restore hearing for profound and severely deaf individuals. CIs convert sounds into electrical pulses which stimulate the auditory nerve fibers. An accurate model of auditory nerve fibers (ANFs) would help in improving the functionality of CIs. Previous studies have shown that the original Hodgkin-Huxley (1952) model (with kinetics adjusted for mammalian body temperature) may be better at describing nodes of Ranvier in ANFs than models for other mammalian axon types. However, the Hodgkin-Huxley model is still unable to explain a number of phenomena observed in auditory nerve responses to CI stimulation, such as short-term and long-term adaptation, the time-course of relative refractoriness, and stimulus-dependent random fluctuations in membrane threshold. Recent physiological investigations of spiral ganglion cells have shown the presence of a number of ion channel types not considered in the previous modelling studies, including low-threshold potassium (𝐼^KLT) channels and hyperpolarization-activated cation (𝐼^h) channels. In this thesis, inclusion of these ion channel types in a stochastic Hodgkin-Huxley model is investigated. Four versions of the model are formed and compared: that is, the standard Hodgkin-Huxley model, the standard model with /h only added, the standard model with 𝐼^KLT only added, and finally, the standard model with both h and 𝐼^KLT added. Two group of responses are explored: i) single-pulse responses and ii) pules-train responses. For the single pulse responses, a charge-balanced biphasic stimulus pulse is used. The effect of varying the pulse-width and the interphase gap is investigated for both leading phase polarities. Results are compared to responses for single monophasic stimulus pulses in some cases. Pulse-train responses are investigated for charge-balanced depolarizing-phase leading biphasic pulses at rates of 200, 800, and 2000 pulse/s. Results from single-pulse responses show an increase in spike threshold when one or both of these channel types are included. The addition of 𝐼^KLT increases random threshold fluctuations in the stochastic model, particularly for longer pulse widths. For pulse-train responses, rapid adaptation in spike rate may be resulting from 𝐼^KLT whereas 𝐼^h produces slower "short-term" adaptation. Thus, the simulation results suggest that including 𝐼^KLT and/or 𝐼^h in a Hodgkin-Huxley model improves the accuracy of the model in describing auditory nerve fiber responses during cochlear implant stimulation. / Thesis / Master of Applied Science (MASc)

Speech perception outcomes for people with a prelingual hearing loss, implanted with a cochlear implant in adolescence or adulthood, are characterized by a large degree of variability. Research findings indicate that some recipients do very well and gain significant open set speech perception skills, whilst a large percentage show little or no change in open set speech results, post implant. In studies to-date, mean speech perception scores were typically substantially poorer than those recorded for implant recipients with a postlingual hearing loss. Despite this, the majority of recipients with a prelingual hearing loss implanted with a cochlear implant in adolescence or adulthood reported satisfaction with their implant and used it regularly. Although there have been a number of studies in the area, none has taken a holistic approach and investigated both objective and subjective outcomes for a large group of participants. In addition, no study has employed a multiple regression analysis to investigate which characteristics were associated with speech perception outcomes in people with a prelingual hearing loss implanted with a cochlear implant in adolescence or adulthood. The objectives of the study were to examine speech perception and other outcomes in people with a bilateral prelingual or perilingual hearing loss, implanted with a cochlear implant as an adolescent or adult, and to investigate prognostic factors associated with positive outcomes. The design consisted of a retrospective review of both speech perception outcomes and other outcomes for 38 recipients, diagnosed with a bilateral hearing loss before age 3, and implanted with a cochlear implant at 14 years or older. There were 24 females and 14 males and the average age at initial stimulation was 33 years. All participants were implanted with a Nucleus device at a private audiology clinic (Attune). Four questionnaires were completed by approximately half of the participants – Glasgow Benefit Inventory (GBI); International Outcome Inventory (IOI-CI); Study Questionnaire; and the Hearing Abilities and Quality of Life Scale. The Study Questionnaire was developed specifically for this project and investigated satisfaction, benefit and advantages/disadvantages of the implant. The Hearing Abilities and Quality of Life Scale was developed by Attune and was completed by recipients pre and post implant. It evaluated the ability to understand conversation in different situations, environmental awareness, safety concerns, involvement in social activities and impact of the hearing loss on relationships. Approximately one third of participants scored between 30 and 90% on the CID/ CUNY test administered via CD post implant and approximately one fifth scored over 90%. The mean score on the CID/CUNY test administered via CD was 8% pre implant and 48% post implant. Over 80% of recipients used their device more than 8 hours a day and all recipients reported being satisfied with it. Three factors accounted for 65% of the variance on the open set sentence test score, post implant. These were stable versus progressive loss, mode of communication in childhood and time without a hearing aid on the implant ear. For the purposes of this research, a ‘stable’ loss was defined as a bilateral severe to profound hearing loss at diagnosis and a ‘progressive’ loss was one that deteriorated to this degree at some point after diagnosis. The findings from this study reveal that a cochlear implant is a viable option for adults and adolescents with a prelingual hearing loss. The majority of participants gained benefit from the device and were satisfied with it. In addition, a substantial number gained good open set speech perception ability, post implant. Consistent with previous studies, there was large intersubject variability in speech scores. The recipients who had a progressive loss, used oral communication in childhood and wore a hearing aid on the implant ear up to the time of surgery were more likely to obtain better speech perception outcomes.

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