Graeme Clark Collection

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1991 - 1997 13
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Author: McDermott, Hugh × Author: McKay, Colette × End date: 1999 × Start date: 1990 × Subject: cochlear implant ×

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    The spectral maxima sound processor: recent findings in speech perception and psychophysics
    McKay, Colette M. ; McDermott, Hugh J. ; Vandali, Andrew E. ; Clark, Graeme M. (Wien, 1994)
    The Spectral Maxima Sound Processor (SMSP) was developed at the University of Melbourne for use with the Mini System 22 implant manufactured by Cochlear Pty Ltd. The SMSP has been shown in recent studies to provide improved speech perception to implantees when compared to the currently commercially available processor for this implant (the MSP (MULTIPEAK) processor). In the first of three experiments, the effect on speech perception of increasing the rate of stimulation of the SMSP and of increasing the number of electrodes activated in each stimulation cycle was studied. It was found that these parameter changes made little difference to speech perception in quiet but both changes were advantageous for some subjects when listening in noise. The second and third experiments investigated psychophysically the effects of two aspects of the SMSP strategy which differ from previous processors for this implant. In the second experiment, it was found that concurrent stimulation of two adjacent or nearby electrodes evoked a pitch which was intermediate to that of either electrode. This may explain, in part, the better discrimination of vowel formants by users of the SMSP. In the third experiment, it was found that a pitch related to the modulation frequency was evoked by amplitude-modulating a constant rate stimulus, provided that the rate of stimulation was sufficiently high (four times the modulation frequency) or a multiple of the modulation frequency. This result may explain the equal ability of SMSP and MSP users to perceive speaker differences and intonation patterns, even though the rate of stimulation is constant In the SMSP.
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    A portable programmable digital sound processor for cochlear implant research
    McDermott, Hugh J. ; Vandali, Andrew E. ; van Hoesel, Richard J. M. ; McKay, Colette M ; HARRISON, MARK ; Cohen, Lawrence T. ( 1993)
    A programmable sound processor which utilizes digital signal processing has been developed for hearing prosthesis research. It incorporates a Motorola DSP56001 integrated circuit, 32K words of memory, a 12 b analog-to-digital converter, and a data formatter and transmitter which conveys control codes to the receiver-stimulator of a cochlear implant. The processor is pocket-sized and battery powered. It has been programmed to emulate the Spectral Maxima Sound Processor for the University of Melbourne/Nucleus 22 electrode implant, and is currently being used by several implantees. In continuing research, speech processing programs are being improved, and other applications, including signal processing for binaural implants and advanced hearing aids, are being developed.
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    A new portable sound processor for the University of Melbourne/ Nucleus Limited multielectrode cochlear implant
    McDermott, Hugh J. ; McKay, Colette M. ; Vandali, Andrew E. ( 1992)
    Abstract not available due to copyright.
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    Place pitch perception with multiple electrode cochlear implants: the use of concurrent activation of nearby electrodes to produce additional ptich percepts [Abstract]
    McDermott, Hugh J. ; McKay, Colette M. ( 1992)
    In multiple electrode cochlear implants, each electrode produces a pitch percept which is usually related monotonically to its distance from the round window. The number of these pitch percepts is limited by the number of usable electrodes and their discriminability, varying up to a maximum of 22 for the mini-system 22 implant but sometimes significantly less. A study on two implanted subjects in which the pitch of pulse trains on two concurrently activated nearby electrodes was compared with the pitch produced when each of the electrodes was activated on its own, showed that the pitch of the concurrently activated electrodes was different from each component electrode and was placed in an intermediate position. Furthermore the pitch of the concurrent stimulation could be altered by adjusting the relative current levels on the two component electrodes. This may partly explain the improvements, particularly in vowel discrimination, obtained with the SMSP strategy described in the accompanying paper.
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    Preliminary results with a six spectral maxima speech processor for The University of Melbourne/Nucleus multiple electrode cochlear implant
    McKay, Colette M. ; McDermott, Hugh J. ; VANDALI, ANDREW ; Clark, Graeme M. ( 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.
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    Speech cues for cochlear implantees: spectral discrimination
    Henry, Belinda, A. ; McKay, Colette M. ; McDermott, Hugh, J. ; Clark, Graeme M. (Monduzzi Editore, 1997)
    The relationship between the ability of cochlear implantees to perceive speech and their ability to discriminate between stimulation on adjacent electrodes was investigated. Speech perception ability was assessed with monosyllabic words in 8 users Nucleus cochlear prosthesis. The ability of these subjects to discriminate between stimulation on adjacent electrodes, in of random loudness differences between electrodes was determined. Results were averaged in the apical, mid and basal regions of the cochlea. Regression analysis showed that speech perception ability and electrode discrimination ability were correlated in the apical to mid region of the cochlea. but the two factors were not correlated in the basal region. Therefore, these results suggest that implantees require the ability to discriminate between stimulation on adjacent electrodes in the apical to mid region of the cochlea in order to achieve high speech perception scores.
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    Speech cues for cochlear implantees: spectral discrimination [Abstract]
    Henry, Belinda, A. ; McKay, Colette M. ; McDermott, Hugh, J. ; Clark, Graeme M. ( 1997)
    The ability of cochlear implantees to understand speech varies over a wide range. While some implantees achieve scores close to 100 % open set word tests, other require visual cues to achieve a significant score on these tests. The focus of this research is to investigate reasons for the wide range of ability and therefore to improve the speech processors used by individual implantees. This study first investigated whether the relative importance of various frequency regions of the speech spectrum differs for implantees of different performance levels, and for implantee groups compared to normally hearing subjects.
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    Musical pitch perception by a user of the Nucleus 22-electrode cochlear implant [Abstract]
    McDermott, Hugh J. ; McKay, Colette M. ( 1995)
    The study of how musical sounds are perceived by users of cochlear implants is both interesting and rewarding. In particular, it has the potential to provide detailed information on the perception of pitch with electrical stimulation of the auditory nerve. However, it is difficult to find subjects whose understanding of musical terminology and memory of conventional musical pitch relationships are adequate for this research. In our Melbourne laboratory, we have been fortunate to locate one implant user who received several years' formal training in the tuning of musical instruments before he lost his hearing. This subject is capable of estimating musical intervals in an open-set context, and can also adjust the interval between two "notes" to match a given target. Experiments involving both estimation and production of musical intervals have been carried out. Several parameters of the electrical stimulation have been varied to create notes of different pitches. These include the rate of steady pulse trains delivered to a fixed electrode position; the place of stimulation with a constant pulse rate; selected combinations of rate and place; and the frequency of sinusoidally amplitude-modulated (SAM) pulse trains delivered to a fixed electrode position. The results show that when pulse rate is the variable parameter, the rate ratio for a given musical interval closely approximates that for acoustic signals, provided that the electrode used is in the apical region of the cochlea. When the stimulation is moved to more-basal positions, the rate ratios become larger than the corresponding acoustic frequency ratios. Changing the place of stimulation with a constant pulse rate causes pitch changes that are comparable with the presumed place-to-characteristic frequency mapping of the subject's electrode array. Combinations of place and rate variation result in more complex effects, in which the pitch associated with the place of stimulation generally dominates, but is affected by the rate. The pitch of SAM pulse trains, although probably weaker than that of unmodulated low-rate pulse trains, is related to the modulation frequency. The ratio of modulation frequencies required for a given musical interval is larger than the corresponding ratio of acoustic frequencies in normal hearing.
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    Current advances in speech processing for the mini-system 22 implant [Abstract]
    McKay, Colette M. ; McDermott, H. J. ( 1992)
    The Spectral Maxima Sound Processor (SMSP) has been developed at the University of Melbourne for use with the mini-system 22 cochlear implant manufactured by Cochlear Pty Ltd. Studies with adult subjects have shown that perception of vowels, consonants, words. and sentences in quiet and in background noise is enhanced with the SMSP when compared with the MSP(MULJIPEAK) currently supplied for use with this implant. Studies comparing the ability of subjects to identify speakers and to identify intonation patterns have shown no reduction due to the SMSP's use of a constant rate of electrical stimulation. Qualitative remarks of subjects are consistent with improved perception in background noise and of degraded speech such as with TV and telephone use. They also report that environmental noises and music sound more natural. Further development of the SMSP strategy and formulation of new strategies are being facilitated by a new programmable processor utilising digital signal processing.