Graeme Clark Collection

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Author: McDermott, Hugh × Author: McKay, Colette × End date: 1997 × Start date: 1992 × Subject: speech perception ×

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Now showing 1 - 6 of 6
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    The importance of different frequency bands to the speech perception of cochlear implantees [Abstract]
    Henry, Belinda A. ; McKay, Colette M. ; McDermott, Hugh J. ; Clark, Graeme M. ( 1996)
    It is well known that cochlear implantees exhibit a wide range of speech perception ability. Understanding the reason for this variability may lead to improved speech processors. This study investigates whether implantees rely on different areas of the speech spectrum for speech cues, compared to normally hearing listeners, and whether poor performers rely on different spectral areas than better performers. Six subjects with the Mini System 22 implant and using the SPEAK strategy participated in this experiment. Scores for monosyllabic words were obtained using the full speech spectrum and with selected frequency bands removed from the subjects’ speech processor maps. The Articulation Index (AI) is a measure of the proportion of speech information available to a listener, and the relative contribution to AI from different frequency bands is termed the Importance Function. The five frequency bands studied in this experiment were determined to be of equal importance to normally hearing listeners for the speech material used. The scores for each implantee were transformed into AI values, and hence the relative importance of the bands was determined. This relative importance was compared between the implantee group and normally hearing listeners to determine the way in which speech perception by electrical stimulation varies from that by acoustical stimulation. Comparisons were also made between individual implantees to determine whether correlations exist between their speech perception ability and their use of cues in different parts of the spectrum. Further research will determine whether the differences among implantees are correlated with their ability to perceive changes in stimulation place or temporal characteristics.
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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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    Speech processing for multichannel cochlear implants: variations of the Spectral Maxima Sound Processor strategy
    McKay, Colette M. ; Vandali, Andrew E. ; McDermott, Hugh J. ; Clark, Graeme M. ( 1994)
    The Spectral Maxima Sound Processor (SMSP) incorporates a bank of 16 band-pass filters which are assigned to 16 intracochlear electrodes. In each stimulation period 6 electrodes are activated, based on the outputs of the filters with the largest amplitudes. The SMSP has previously been compared with the present MSP (MULTIPEAK) processor and found to improve speech comprehension results. The SMSP speech processing scheme has recently been implemented successfully in a new speech processor, also developed at the University of Melbourne, which utilises digital signal processing techniques. The programming flexibility of this processor has facilitated the investigation of variations of the SMSP strategy which might provide further enhancement of speech perception. Three variations have been investigated: firstly, increasing the constant pulse rate from the usual 250 Hz to 400 Hz; secondly, changing the number of electrodes selected in each stimulation period from 6 to numbers between 4 and 8; thirdly, sharpening the spectral peaks prior to selection of the active electrodes. The results of these studies showed that all three variations had minimal effect on speech perception in quiet, but that increasing the number of electrodes selected for stimulation to 8, or increasing the rate of stimulation, was advantageous for some subjects when listening in background noise.
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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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    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.