Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 10 of 12
-
ItemSpeech results with a bilateral multi-channel cochlear implant subject for spatially separated signal and noise( 1999)Speech tests in noise were administered to a bilaterally implanted cochlear implant subject. Performance for simultaneous use of two identical implants, with the same speech processing strategy on two independent standard clinical processors, was compared with that of the better performing monaural side alone. Speech was presented at an angle of 45 degrees toward one ear, with noise at 45 degrees toward the contralateral side. Tests were also administered for speech and noise reversed in location. When the speech signal was on the same side as the subject's better performing ear, monaural and binaural tests resulted in similar scores. When the speech was on the opposite side, however, the binaural condition showed significantly better speech scores. The results indicate that binaural implants can provide improved performance in noise when speech and noise arc spatially separated.
-
ItemSpeech perception in implanted children: influence of preoperative residual hearing on outcomes [Abstract]( 1998)Since the first child was implanted with the Nucleus 22-channel prosthesis in Melbourne in 1985, several thousand children world-wide have now benefitted from this technology. More effective paediatric assessment and management procedures have now been developed, allowing cochlear implants to be offered to children under the age of 2 years. Improvements in speech processing strategy have also been implemented in the Nucleus implant system, resulting in increased mean speech perception benefits for implanted adults. Although a range of performance on formal measures of hearing, speech or language has been reported for children using implants, results from the first decade of implant experience consistently show that significant benefits are available to children receiving their implant at an early age. Reported speech perception results for implanted children show that a considerable proportion (60%) of paediatric patients in the Melbourne and Sydney clinics are able to understand some open-set speech using electrical stimulation alone. These results, and the upward trend of mean speech perception benefits shown for postlinguistically deafened adults have raised questions as to whether severely, or severely-to-profoundly deaf children currently using hearing aids would in fact benefit more from a cochlear implant. To investigate the potential influence of the degree of preoperative residual hearing on postoperative speech perception, results for all implanted children in the Melbourne and Sydney cochlear implant programs were analysed. Results showed that as a group, children with higher levels of preoperative residual hearing were consistently more likely to achieve open-set speech perception benefits. Potential factors in this finding could be higher levels of ganglion cell survival or greater patterning of the auditory pathways using conventional hearing aids prior to implantation. Conversely, children with the least preoperative residual hearing were less predictable, with some children achieving open-set perception, and others showing more limited closed-set benefits to perception. For these children, it is likely that preoperative residual hearing is of less significance than other factors in outcomes.
-
ItemComparison of the SPEAK (Spectral Maxima) and multipeak speech processing strategies and improved speech perception in background noise( 1995)As more is known about speech processing for Cochlear Implant patients, results should continue to improve. It now appears possible that Cochlear Implant patients may, in some instances, reach performance levels that are better than those obtained by most severely deaf people who use hearing aids.
-
ItemThe development of the Melbourne/Cochlear multiple-channel cochlear implant for profoundly deaf children( 1992)In 1978-79, a speech processing strategy which extracted the voicing (FO) and second formant (F2) frequencies and presented these as rate and place of stimulation respectively to residual auditory nerve fibres was developed for the University of Melbourne's prototype multiple-channel receiver-stimulator (Clark et aI1977, Clark et a11978, Tong et aI1980). This speech processing strategy was shown to provide post linguistically deaf adults with some open-set speech comprehension using electrical stimulation alone, and considerable help when used in combination with lipreading (Clark et al 1981).
-
ItemPreliminary results with a six spectral maxima speech processor for The University of Melbourne/Nucleus multiple electrode cochlear implant( 1991)An improved sound processor for a multiple-channel cochlear implant hearing prosthesis has been developed. The spectral maxima sound processor (SMSP) extracts the six largest frequency components of speech and presents stimuli at a rate of 250 Hz to electrodes at positions selected on the basis of the spectral frequencies. It was designed for use initially with the advanced cochlear implant recently developed at the University of Melbourne, which is capable of high rate and quasi-simultaneous stimulation. The present study, however, was carried out with two subjects who have the more widely used 22-electrode implant produced commercially by Cochlear Pty Limited (formerly Nucleus Limited). Preliminary results comparing the performance of the SMSP with that of previous speech processing techniques (F0/F1/F2 strategy) are presented. The results indicate that the SMSP is capable of providing implanters with significantly greater information about speech.
-
ItemParameter selection and programming recommendations for the ACE and CIS speech processing strategies [Abstract]( 1999)The Nucleus 24 Cochlear Implant system with the SPrint processor provides access to multiple speech processing strategies and a wide range of programming parameters. Strategy comparison studies have suggested that the optimal parameter set and coding strategy varies from individual to individual. It is necessary, however, to establish some default programming parameters and fitting guidelines. Therefore we have investigated the effect of stimulation rate and the number of channels or maxima in the ACE or CIS strategies, as well as the optimal programming strategy for subjects with a limited number of available electrodes. Speech perception was tested using monosyllabic words and sentences in noise, with the evaluation protocol designed to take into account learning effects. Take-home experience was provided with all programs, and subjects were asked to complete a comparative performance questionnaire regarding program preference. Six or eight subjects were enrolled in each study.
-
ItemAn analysis of high rate speech processing strategies using the Nucleus 24 cochlear implant [Abstract]( 1998)The effects of varying the stimulation rate on speech perception was evaluated in five postlinguistically deaf adult users of the Nucleus 24 Cochlear Implant System. Three different rates of electrical stimulation, 250, 807, and 1615 pulses per second per channel were employed. For the high stimulus rate the analysis frequency was the same as for the medium rate condition. The study investigated the effect of varying rate of stimulation when using the electrode selection technique of the SPEAK strategy. The study used a repeated ABC experimental design, in order to account for learning effects and to minimize ordering effects. Speech perception was evaluated using both monosyllabic words (open-sets of CNC words in quiet) and sentence materials (open-sets of CUNY sentences at signal-to-noise ratios from +20 to 0dB). In addition, the subjects' perception of closed-sets of 19 vowels and 24 consonants, presented in the H/VID and A/C/A context, were also investigated. The recognition and perception of distinctive features were assessed across strategies and patients. Preliminary speech perception results have shown no statistically significant difference in performance between the low and medium stimulation rates. However, significantly poorer results were observed for the high rate condition for some tests with some individuals. Individual differences may be explained by the effects of rate of stimulation on speech features.
-
ItemAn analysis of high rate speech processing strategies using the Nucleus 24 cochlear implant [Abstract]( 1998)Speech comprehension for a group of five users of the Nucleus 24 Cochlear Implant system was explored at three rates of electrical stimulation, 250, 807, and 1615 pulses per second per channel. For the high stimulus rate the analysis frequency was the same as for the medium rate condition. The study investigated the effect of varying rate of stimulation when using the electrode selection technique of the SPEAK strategy. This has been undertaken using a repeated ABC experimental design to account for learning and minimize ordering effects. Speech perception was assessed using open-sets of CNC words in quiet and open-sets of CLTNY sentences at signal-to-noise ratios from +20 to 0dB. Closed-sets of 19 vowels and 24 consonants were also presented, in the H/V/D and A/C/A context. The recognition and perception of distinctive features were assessed across strategies and patients. Preliminary speech perception results have shown no statistically significant difference in performance between the low and medium stimulation rates. However, significantly poorer results were observed for the high rate condition for some tests. Individual differences may be explained by the effects of rate of stimulation on speech features.
-
ItemAdvances in cochlear implant speech processing(Monduzzi Editore, 1997)A cochlear implant is a device which restores some hearing in severely-to-profoundly deaf people when the organ of Corti has not developed or is destroyed by disease or injury to such an extent no comparable hearing can be obtained with a hearing aid. When the organ of Corti is severely malfunctioning or absent, sound vibrations cannot be transduced into temporo-spatial patterns of action potentials along the auditory nerve for the coding of frequency and intensity. As a result, a hearing aid which amplifies sound is of little or no use. Our early research (Clark, 1969) emphasized that with electrical stimulation there was an electro-neural "bottle-neck" restricting the amount of speech and other acoustic information that could be presented to the nervous system. It also showed the need to use multiple-channel stimulation presented non-simultaneously, to minimize channel interaction (Clark, 1987).
-
ItemTemporal coding in auditory neurons to electrical stimulation [Abstract]( 1997)The temporal response of the auditory pathway following intracochlear electrical stimulation will reflect the level of encoded temporal information, which is important for the further developmentof cochlear implant speech processing strategies, and in tum lead to a better understanding of temporal coding of acoustic stimuli Temporal coding of sound frequencies is based on the phase or time locked neural response seen to low frequency acoustic stimuli. The ability of neurons to respond in a time locked manner may determine the degree of encoded temporal frequency information. Electrophysiological studies have shown that the degree of response synchrony to charge balanced biphasic electrical stimuli is far greater than that seen to acoustic stimuli. We have investigated the temporal response properties of single units in the anteroventral cochlear nucleus (AVCN) in the cat to rates of electrical stimulation up to 800 pulses/s.