Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemThe surgery for multiple-electrode cochlear implantations(Cambridge University Press, 1979)The multiple-electrode hearing prosthesis designed in the Departments of Otolaryngology and Electrical Engineering (UMDOLEE) at the University of Melbourne (Clark et al., 1977) has been miniaturized with hybrid circuitry so that, if design changes are necessary as a result of initial patient testing, they can be made at minimal cost. This results, however, in increased package dimensions which makes its placement and the design of the surgery more critical. This problem is increased by the fact that we have considered it important to be able to remove the package and replace it with another without disturbing the implanted electrode array, should the first receiver-stimulator fail or an improved design become available. This has meant the design of a special connector (Patrick, 1977; Clark et al., 1978) which adds to the dimensions of the implanted unit. In addition the placement of the coils for transmitting power and information has to be considered. Not only is it desirable to site the coils at a convenient location behind the ear to facilitate the placement and wearing of the external transmitter, but there should also be no relative movement between the coils and the electronic package. These design considerations have led to the sitting of the coils on top of the hermetically-sealed box, and further increased the height of the package. The dimensions of the package shown in Fig. 1 are length 42 mm, width 32 mm, height of connector 8.5 mm, height of receiver-stimulato unit 13 mm. The surgical considerations discussed are the result of a number of temporal bone and cadaver dissections, and the surgical implantation at The Royal Victorian Eye and Ear Hospital of the UMDOLEE unit in a specially-selected patient.
-
ItemCochlear implantation in children: labyrinthitis following pneumococcal otitis media in unimplanted and implanted cat cochleas( 1994)Pneumococcal otitis media is frequent in young children and could lead to labyrinthitis post-implantation. To assess the risk and methods of minimizing it by a graft to the round window around the electrode entry point, we have used a cat animal model of pneumococcal otitis media. Twenty-one kittens were used in the study. Thirty-two cochleas were implanted when the kittens were 2 months of age. Fourteen cochleas were implanted without using a graft (12 were available for study); 9 had a fascial graft, and 9 a Gelfoam® graft (7 were available for study). The implanted kittens had their bullae inoculated with Streptococcus pneumoniae 2 months after implantation and were sacrificed 1 week later. There were also 9 unimplanted control ears which were inoculated when the animals were 4 months of age. Labyrinthitis occurred in 44% of unimplanted control, 50% of implanted ungrafted, and 6% of implanted grafted (fascia and Gelfoam®) cochleas. There was no statistically significant difference between the unimplanted control and the implanted cochleas (p < 0.05). There was, however, a difference between the implanted-ungrafted and implanted grafted cochleas, but not between the use of fascia and Gelfoam® to graft the round window entry point. As a result, the data indicates that cochlear implantation does not increase the risk of labyrinthitis following pneumococcal otitis media, but it is desirable to use fascia as a graft to the round window around the electrode entry point.
-
ItemPerception of connected speech without lipreading, using a multi-channel hearing prosthesis( 1986)Four of 13 totally deaf patients implanted with the Nucleus multi-channel hearing prosthesis at the University of Melbourne have demonstrated the ability to understand connected speech without lipreading or other visual cues. These patients were able to repeat verbatim unknown material read by a tester at rates of up to 35 words per minute. They were also able to understand an average of 78%, of key word, in everyday sentences in ideal acoustic conditions and 51% of equivalent material over the telephone. These results show that with a good proportion of postlingually deaf patients the multi-channel hearing prosthesis can not only act as an aid to lipreading. but also restore effective speech understanding without lipreading.
-
ItemA signal processor for a multiple-electrode hearing prosthesis( 1984)A 22-electrode implantable hearing prosthesis uses a wearable speech processor which estimates three speech signal parameters. These are voice pitch, second formant frequency and flattened spectrum amplitude. The signal is monitored continuously for periodicity in the range 80-400 Hz and, if this is present, stimulation occurs at the same rate. Otherwise, as in the case of unvoiced sounds, it occurs at the random rate of fluctuation of the signal envelope. The second formant is obtained by filtering to extract the dominant peak in the midband region and by continuous measurement of the zero crossing rate. The amplitude measured is that of the whole speech spectrum pre-emphasized by differentiation. The values that are presented to the patient are the parameter estimates immediately prior to the stimulation pulse. Second formant frequency is coded by selection of an appropriate electrode in the cochlea and amplitude by a suitably controlled current. Automatic gain control is used to keep the dynamic range of the amplitude estimate within the 30 dB range of the circuitry.