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Melbourne, Australia

Monksfield P.,University of Melbourne | Husseman J.,University of Melbourne | Cowan R.S.C.,HEARing CRC | O'Leary S.J.,University of Melbourne | Briggs R.J.S.,University of Melbourne
Cochlear Implants International | Year: 2012

Objective: The Nucleus 5 or CI500 series cochlear implants are the new generation of Nucleus® cochlear implants. The receiver-stimulator package has a low profile without a pedestal projecting from the medial surface. This study aimed to demonstrate that the new design can facilitate a minimally invasive surgical approach, without the need for tie-down sutures and without a seat drilled for the receiver-stimulator package. Methods: The surgical technique involved placing the device directly on the surface of the bone in a secure sub-periosteal pocket with a channel drilled for the lead. A well or ramped seat was not drilled and tie-down sutures were not used. Measurements were taken from the transmitting coil to the tragus and the coil to the lobule immediately after implantation, and serially thereafter to document implant position. Results: To date, over 200 implants have been performed with the Nucleus 5 device. In all cases, healing was uneventful without major complications. Of 137 patients with at least 6-week follow-up data, 8% showed a measurement change of greater than 1 cm whereas only 4.4% demonstrated any clinically evident movement. None had any complications relating to migration and none required repositioning of the device. Discussion: The new design can safely be inserted without drilling a well for the receiver-stimulator package. Some early post-operative movement of the package was observed which caused no clinical impact. This modified surgical technique reduces the risk of intracranial complications and reduces operating time. © W.S. Maney & Son Ltd 2012. Source

Salloum C.A.M.,University of Toronto | Wong D.D.E.,University of Toronto | Papsin B.C.,University of Toronto | Van Hoesel R.,HEARing CRC | Gordon K.A.,University of Toronto
Ear and Hearing | Year: 2010

Objectives: Interaural level differences (ILD) and interaural timing differences (ITD) are important cues for locating sounds in space. Adult bilateral cochlear implant (CI) users use ILDs more effectively than ITDs. Few studies investigated the ability of children who use bilateral CIs to make use of these binaural cues. Our working hypothesis was that children using bilateral CIs are able to perceive changes in ITDs and ILDs similar to their normal-hearing (NH) peers. Design: Participants were two groups of children; 19 bilateral implant users (CI) and nine NH children. The children in the CI group had received a second CI after 4.9 ± 2.8 yrs of unilateral use. Children performed a four alternative forced-choice lateralization task in which they were asked to describe stimuli as coming from the left side, right side, middle of the head, or from both sides simultaneously. Stimuli were 500 msec trains of electrical pulses delivered to apical electrode no. 18 (CI group) or clicks (NH group) presented 11 times per second with either ITDs (0, 400, 1000, or 2000 μsec delay between sides) or level differences (0, 10, or 20 Current Units (CI group) or 0, 10, or 20 dB (NH group) difference between sides). ITDs were presented using current levels that were balanced using left and right electrically evoked brain stem responses. Stimulus levels evoking response amplitudes that were most similar were used. Results: Responses from children in the CI group changed significantly with changes in ILD of bilateral stimuli, but not with changes in ITD. Responses from children in the CI group were significantly different from those in the NH group in three ways. Children in the CI group perceived bilaterally presented electrical pulses: (1) to come from the second implanted side more often than the first, (2) to rarely come from the middle, and (3) to come from both sides of the head simultaneously. Perceived changes in lateralization with ILD changes were correlated with differences in amplitudes of electrically evoked brain stem responses by the left versus right CI. Conclusions: The results of this study illustrate that children who use bilateral CIs can lateralize stimuli on the basis of level cues, but have difficulty interpreting interimplant timing differences. Perceived lateralization of bilaterally presented stimuli to the second implanted side in many of the stimulus conditions may relate to the use of different device generations between sides. Further differences from normal lateralization responses could be due to abnormal binaural processing, possibly resulting from a period of unilateral hearing before the provision of a second implant or due to insufficiently matched interimplant stimuli. It may be possible to use objective measures such as electrically evoked auditory brain stem responses wave eV amplitudes to provide balanced levels of bilateral stimulation in children who have had no binaural hearing experience. © 2010 Lippincott Williams & Wilkins. Source

Newbold C.,HEARing CRC | Newbold C.,University of Melbourne | Peters L.,University of Melbourne | Cowan R.,HEARing CRC | And 2 more authors.
Audiology and Neurotology | Year: 2014

Cochlear implant stimulation creates a reduction in electrode impedance that returns to pre-stimulation levels following cessation of stimulation and is presumed to be associated with the fibrous tissue covering over the electrode array. This study assessed the possibility that transitory impedance reduction originates from a change in the membrane permeability of cells on the electrode (electropermeabilization). These changes can be recorded using the dye propidium iodide, which fluoresces upon entry into the leaky cell. The in vitro model used showed impedance reduction and dye uptake into adherent cells overlying planar gold electrodes stimulated with as little as 5 min of clinically relevant cochlear implant stimulation. The delayed additions of propidium iodide showed a similar dye uptake to those groups with concurrent dye addition, suggesting the electropermeabilization was not reversible. Further understanding of the mechanisms behind these impedance and cell permeability changes with cochlear implant electrical stimulation may provide opportunities for creating longlasting reductions in electrode impedance. © 2014 S. Karger AG, Basel. Source

Vandali A.E.,HEARing CRC | Van Hoesel R.J.M.,HEARing CRC
Journal of the Acoustical Society of America | Year: 2012

The abilities to hear changes in pitch for sung vowels and understand speech using an experimental sound coding strategy (eTone) that enhanced coding of temporal fundamental frequency (F0) information were tested in six cochlear implant users, and compared with performance using their clinical (ACE) strategy. In addition, rate- and modulation rate-pitch difference limens (DLs) were measured using synthetic stimuli with F0s below 300 Hz to determine psychophysical abilities of each subject and to provide experience in attending to rate cues for the judgment of pitch. Sung-vowel pitch ranking tests for stimuli separated by three semitones presented across an F0 range of one octave (139-277 Hz) showed a significant benefit for the experimental strategy compared to ACE. Average d-prime (d') values for eTone (d'=1.05) were approximately three time larger than for ACE (d'=0.35). Similar scores for both strategies in the speech recognition tests showed that coding of segmental speech information by the experimental strategy was not degraded. Average F0 DLs were consistent with results from previous studies and for all subjects were less than or equal to approximately three semitones for F0s of 125 and 200 Hz. © 2012 Acoustical Society of America. Source

Vandali A.E.,HEARing CRC | Van Hoesel R.J.M.,HEARing CRC
Journal of the Acoustical Society of America | Year: 2011

A sound-coding strategy for users of cochlear implants, named enhanced-envelope-encoded tone (eTone), was developed to improve coding of fundamental frequency (F0) in the temporal envelopes of the electrical stimulus signals. It is based on the advanced combinational encoder (ACE) strategy and includes additional processing that explicitly applies F0 modulation to channel envelope signals that contain harmonics of prominent complex tones. Channels that contain only inharmonic signals retain envelopes normally produced by ACE. The strategy incorporates an F0 estimator to determine the frequency of modulation and a harmonic probability estimator to control the amount of modulation enhancement applied to each channel. The F0 estimator was designed to provide an accurate estimate of F0 with minimal processing lag and robustness to the effects of competing noise. Error rates for the F0 estimator and accuracy of the harmonic probability estimator were compared with previous approaches and outcomes demonstrated that the strategy operates effectively across a range of signals and conditions that are relevant to cochlear implant users. © 2011 Acoustical Society of America. Source

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