Graeme Clark Collection
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ItemAccuracy of behavioural threshold prediction using steady-state evoked potentials [Abstract]( 1994)This paper examines the confidence with which predictions of hearing level can be made using the steady-state evoked potential (SSEP) technique. Steady-state evoked potentials are scalp potentials that can be elicited in response to sinusoidally amplitude and/or frequency modulated tones in sleeping or awake subjects. SSEP thresholds were obtained using frequency specific stimuli at octave frequencies between 250Hz and 4000Hz in 25 children and 35 adults with varying degrees of sensori-neural hearing loss. These levels, determined automatically by a computerised detection system, were then compared with thresholds obtained behaviourally. Linear regression analyses of this data have shown that the SSEP procedure allows objective estimates of hearing level to be made for a range of carrier frequencies to within 10dB accuracy on 96% of occasions.
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ItemThe diagnostic assessment of infants using steady-state evoked potentials [Abstract]( 1994)This paper examines the relationship between the steady-state potential and behavioural thresholds obtained in two groups of young children. The first group consists of 10 babies referred to the Victorian Children's Hearing Centre following abnormal findings on screening ABR assessments. The second group contains 20 difficult to test infants who had unconfirmed hearing losses at the time of the SSEP assessment. The hearing levels predicted by the regression lines (described in the companion paper presented at this conference) were in close agreement with the behavioural levels obtained subsequently from children in both groups.
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ItemSpeech perception results in children using the 22-electrode cochlear implant [Abstract]( 1990)Twenty-one profoundly hearing impaired children ranging in age from 3 to 20 years have been implanted with the 22-electrode cochlear implant (Cochlear Pty ltd) at the University of Melbourne Cochlear Implant Clinic. Five children (aged 6.0 to 14.8 years) have achieved substantial scores on open set speech tests using hearing without lipreading. Phoneme scores in monosyllabic words ranged from 30% to 72%. Word scores in sentences ranged from 26% to 74%. Four of these five children were implanted during preadolescence and the fifth who had a progressive loss, was implanted during adolescence. Eight children (aged 3.0 to 11 years), have either been implanted recently or are too young for detailed assessments. However some have shown using closed set speech perception tests or vowel imitation tasks, that they are beginning to use the auditory input provided by the implant. The remaining children (aged 13.11 to 20.1 years) have not demonstrated open set recognition but are all full time users of the device. This group was implanted during adolescence after a long duration of profound deafness. The results will be discussed with reference to a number of variables which may contribute to successful implant use; such as age of onset of deafness, duration of deafness. age of implantation, educational program and type of training.
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ItemResults in children using the 22 electrode cochlear implant [Abstract]( 1989)Abstract not available due to copyright.
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ItemEvoked responses in humans to continuous amplitude modulated tones [Abstract]( 1982)The clinical use of the slow cortical auditory evoked responses and the auditory brainstem response is now widespread. Both of these responses look at the electrical changes in the brain following the onset of an acoustic stimulus and are known as transient responses. This paper will describe a technique of recording electrical potentials evoked during a continuous sinusoidally-modulated amplitude-modulated tone. This type of response is known as a steady-state response. The responses to this type of sound were found to be periodic, having the same fundamental frequencies as the modulation envelope. A Fourier transform was used to quantify the amplitude and phase of the first two harmonic components of the response. Responses can be recorded for modulation rates from 4Hz to 448Hz, for carrier frequencies from 250Hz to 4KHz and for sound pressure levels (SPLs) from 30dBSPL to 100dBSPPL. In general, the response amplitude increases with SPL. Estimates of latencies of these steady-state potentials can be made by measuring the phase of both harmonics as the modulation frequency is varied. Latencies suggest the auditory cortex as one of the sources of the response. The clinical implication of these results will be discussed.
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ItemThe ERA System for steady-state evoked potential recording and analysis [Abstract]( 1998)The ERA System is the first commercially available device designed specifically for the recording and analysis of steady-state evoked potentials. It is the result of basic and applied research carried out at the University of Melbourne over the past 20 years. The basic research that contributed to the development of this project as well as studies of a more applied nature that highlight the clinical utility of SSEP measure will now be reviewed. The automatic detection algorithm employed in the analysis of results will be explained, as well as the linear regression for threshold estimation. The hardware components and software options of the ERA System will be reviewed. In addition, some of the issues involved in the production and distribution of a commercial device for “evoked response audiometry” in both national (Australian) and international (e.g. U.S.A., E.U., Asia) markets will be discussed.