Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 10 of 26
-
ItemPsychophysical studies on cochlear implant patients deafened prior to 4 years of age [Abstract]( 1989)Abstract not available due to copyright.
-
ItemResults for two children using a multiple-electrode intracochlear implant( 1989)Abstract not available due to copyright.
-
ItemThe biologic safety of the Cochlear Corporation multiple-electrode intracochlear implant( 1988)Studies have been undertaken to confirm the biologic safety of the Cochlear Corporation multi-electrode intracochlear implant. The materials used are biocompatible. The electrode array is flexible: it can be inserted with minimal or no trauma, providing the insertion is stopped when resistance is first felt. An atraumatic insertion is facilitated if a good view is obtained along the scala tympani of the basal turn of the cochlea by drilling through the crista fenestrae. The passage of the electrode around the cochlea can be facilitated if the electrode is rotated during insertion (clockwise for the left and anticlockwise for the right cochlea). The electrode can be explanted and another one reinserted with minimal or no trauma. A seal established around the electrode after an implantation period of 2 weeks can prevent infection extending from the middle to the inner ear. The electrical stimulus parameters produced by the Nucleus receiver-stimulator cause no loss of spiral ganglion cells or corrosion of the platinum band electrodes. Long-term stimulation has been carried out for up to 8 years in patients without affecting their clinical performance.
-
ItemThe surgical anatomy for multiple-electrode extracochlear implant operations(Cambridge University Press, 1988)Direct access to the whole length of the cochlear turns via endaural middle ear approach for the placement of extracochlear electrodes is severely restricted. Approximately 10 mm. of the cochlear turns are accessible, being less than a third of their length. The middle cranial fossa, the facial nerve, the internal carotid artery and the temporomandibular joint restrict the access. A further restriction is caused by the position of the cochlea and the direction of its axis. The anterior part of the cochlea lies anterior to the tympanic membrane and medial to the temporomandibular joint, thus limiting an endaural approach to a posterolateral direction. Despite this limitation small sections of the basal, middle and apical turns of the cochlea can be reached.
-
ItemResults for Chinese and English in a multichannel cochlear implant patient( 1987)A multichannel cochlear prosthesis was implanted in a Chinese patient who suffered from profound sensory hearing loss. The preoperative Minimal Auditory Capabilities (MAC) battery tests in English, as well as an open set bisyllable word test, an open set sentence test, and speech tracking in Chinese indicated significant improvement of speech perception for both English and Chinese after the operation. Substantial understanding of running speech was possible in both languages without the help of lipreading.
-
ItemEstimation of the effective spread of neural excitation produced by a bipolar pair of scala tympani electrodes( 1987)Psychophysical studies were conducted on two multichannel cochlear implant patients for electrical stimulation of two bipolar electrode pairs in the human cochlea. Loudness summation was approximately complete for spatial separation of about 3 mm between the two electrode pairs. At comfortable loudness, the effective spread of neural excitation produced by a bipolar pair of scala tympani electrodes was estimated to be 3 to 4 mm on the basis of both loudness summation and forward masking results.
-
ItemEffect of high electrical stimulus intensities on the auditory nerve using brain stem response and audiometry( 1987)The response of the auditory nerve to acute intracochlear electrical stimulation using charge-balanced biphasic current pulses was monitored using electrically evoked auditory brain stem responses (EABRs). Stimulation at moderate charge densities (64 µC cm-2 geom/ phase; 0.8 mA, 200 µs/phase) for periods of up to 12 hours produced only minimal short-term changes in the EABR. Stimulation at a high charge density (144 µC cm-2 geom/phase; 1.8 mA, 200 µs/phase) resulted in permanent reductions in the EABR for high stimulus rates (> 200 pulses per second [pps]) or long stimulus durations (12 hours). At lower stimulus rates and durations, recovery to prestimulus levels was slow but complete. The mechanisms underlying these temporary and permanent reductions in the EABR are probably caused by neural adaptation and more long-term metabolic effects. These findings have implications for the design of speech-processing strategies using high stimulus rates.
-
ItemEducational assessment and management of children with multichannel cochlear implants( 1987)This paper describes the assessment and training program to evaluate speech, language, and communication skills of profoundly deaf children during and after training. Two sensory aids/prostheses are used: hearing aids and the Nucleus multichannel cochlear implant. Using a single-subject time-series experimental design, children's speech, language, and communication skills are assessed. For speech skills, assessment includes formal tests of articulation and intelligibility, syllable stress and process analyses, analyses of suprasegmental features, and voice quality. For general communication abilities, conversational skills with different speakers, story production skills, comprehension and expression of procedural information, discourse skills, and a measure of conversational interaction skills (pragmatics) are analyzed at regular intervals. Regular observations also sample the subjects' mode and frequency of interactions with individuals and groups in the school and home setting. Normative tests and formal analyses of language samples are also used to assess the overall language age of the child, vocabulary size, and kinds of expressive and receptive, syntactic, and semantic ability.
-
ItemTemporal coding of speech information for cochlear implant patients( 1987)A modified speech-processing strategy incorporating the temporal coding of information strongly correlated with the first formant of speech was evaluated in a long-term clinical experiment with a single patient. The aim was to assess whether the patient could learn to extract information from the time domain in addition to the time domain cues for voice excitation frequency already received from the initial strategy. It was found that the patient gained no significant advantage from the modified strategy, but there was no disadvantage either, and the patient expressed a preference for the modified strategy for everyday use.
-
ItemCurrent distributions produced by the banded electrode array: an experimental study conducted with a tank model( 1987)The tank model consisted of a 22-band electrode array lying in a homogeneous normal saline solution in the base of a tube 5 mm in diameter and 4 cm in length. The current distribution was obtained by measuring vector potentials along the longitudinal direction at a given radial distance from the electrode array. The results indicate that when only one pair of electrodes is stimulated, the current distribution is bell shaped. When two pairs are simultaneously stimulated by two isolated current sources, the results demonstrate a vector summation of current density throughout the system.