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R C Dowell

Publications and source records attributed to R C Dowell.

54 records · Page 3Linked to original sources
PubMed1984

Speech processing studies using an acoustic model of a multiple-channel cochlear implant.

The speech perception of two multiple-channel cochlear implant patients was compared with that of three normally hearing listeners using an acoustic model of the implant for 22 different speech tests. The tests used included a minimal auditory capabilities battery, both closed-set and open-set word and sentence tests, speech tracking and a 12-consonant confusion study using nonsense syllables. The acoustic model represented electrical current pulses by bursts of noise and the effects of different electrodes were represented by using bandpass filters with different center frequencies. All subjects used a speech processor that coded the fundamental voicing frequency of speech as a pulse rate and the second formant frequency of speech as the electrode position in the cochlea, or the center frequency of the bandpass filter. Very good agreement was found for the two groups of subjects, indicating that the acoustic model is a useful tool for the development and evaluation of alternative cochlear implant speech processing strategies.

Aged↗
PubMed1984

A signal processor for a multiple-electrode hearing prosthesis.

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.

Cochlear Implants↗
PubMed1984

Clinical results using a multiple-channel cochlear prosthesis.

A total of eight profoundly deaf patients have been implanted with the Nucleus Limited multiple-channel cochlear prosthesis at the University of Melbourne since it became available in late 1982. All patients are everyday users of the device. Speech testing using the device alone has shown consistently high scores for a variety of closed set tests and significant levels of open set speech understanding in most of the patients. Lipreading assessment with phoneme, word, sentence and speech tracking material shows significant improvement when using the prosthesis for all patients tested. Other benefits reported are recognition of environmental sounds, decrease in tinnitus, increased confidence in social and vocational situations and improved voice control. One patient is able to cope with interactive conversations over the telephone and three others are able to use the telephone in a limited way without special codes.

Adult↗
PubMed1983

Clinical trial of a multiple-channel cochlear prosthesis. An initial study in four patients with profound total hearing loss.

The clinical trial of a multiple-channel cochlear prosthesis was undertaken in four patients with postlingual deafness and profound total hearing loss. The results of open-set speech tests confirmed that, using electrical stimulation alone, one patient could have a meaningful conversation without resorting to lipreading (for example, this patient uses the prosthesis to converse with her husband on the telephone). The results of closed-set speech tests also suggested that a multiple-channel stimulator is more effective than a single-channel one in conveying speech information. The cochlear prosthesis was especially effective in all four patients when it was used in conjunction with lipreading, and speech-tracking tests showed that the patients could combine the information obtained from both electrical stimulation and lipreading.

Adult↗
PubMed1983

Two-component hearing sensations produced by two-electrode stimulation in the cochlea of a deaf patient.

Dissimilarities in perception elicited by stimulation with two electrodes were estimated. A two-dimensional spatial configuration was found to be suitable to represent the dissimilarity data, and the two dimensions could be interpreted as corresponding to the position of the apical and basal electrode of the two-electrode combination. A speech-processing strategy that converts acoustic, first and second formants to two-electrode stimulation is proposed.

Cochlea↗
PubMed1983

Psychophysical studies evaluating the feasibility of a speech processing strategy for a multiple-channel cochlear implant.

This paper reports further psychophysical studies on a multiple-channel cochlear implant patient evaluating the feasibility of a speech processing strategy which converts the acoustic fundamental frequency to electric repetition rate, the second-formant frequency to electrode position, and the acoustic amplitude to current level. The first four studies evaluated the use of a special pulse pattern to minimize the loudness variation with electric repetition rate. The chosen pulse pattern consisted of multiple pulses occurring in the first half of each repetitive period (MPP) in contrast to the more conventional pattern with a single pulse per period (SPP). The results showed that MPP approximately equalized the loudness variation with repetition rate. The dynamic range of current, the pitch variation with repetition rate, and the difference limens for repetition rate were found to be similar to MPP and SPP. Two other studies investigated interaction between electrode position and repetition rate (RR). The first of these showed that the patient could make use of information provided by rising or falling RR trajectories superimposed on individual electrodes or electrode trajectories as an indicator of the direction of intonation variation. The second of these studies showed that the dissimilarities amongst the hearing sensations produced by steady-state stimuli differing in electrode position and repetition rate were characterized by two perceptual components, relating to the two electric parameters, respectively.

Cochlear Implants↗
PubMed1983

Preoperative hearing and evaluations for cochlear implant patients. A preliminary report using a Minimal Auditory Capabilities battery.

Two profoundly deaf patients were evaluated using the Minimal Auditory Capabilities (MAC) battery of speech discrimination tests. One patient was a multiple-channel cochlear implant patient (MC1) using a wearable speech-processor, the other a prospective cochlear implant patient using a hearing aid (HA). Results from the MAC battery showed that MC1 received significantly more auditory information via the speech-processor than was provided by the hearing aid to HA. These results indicated that the cochlear implant could be a suitable alternative for HA. However, the results indicated that HA gained some minimal benefit from the hearing aid and these results should be taken into consideration when deciding which ear should be implanted.

Cochlear Implants↗
PubMed1982

A 12-consonant confusion study on a multiple-channel cochlear implant patient.

A consonant confusion study was undertaken on a multiple-channel cochlear implant patient using a wearable speech processing device. This patient suffered from total bilateral deafness acquired postlingually. The consonants /b/, /p/, /m/, /v/, /f/, /d/, /t/, /n/, /z/, /s/, /g/, /k/ were presented in a VCV context with the vowel /a/ as in father by a male and female speaker under three conditions: lipreading alone; electrical stimulation alone using the wearable speech processor and multiple-channel cochlear implant; lipreading in conjunction with electrical stimulation. No significant difference was detected between the results for the male and female speakers. The percentage correct scores for the pooled results of both speakers were lipreading alone--30%; electrical stimulation alone--48%; lipreading with electrical stimulation--70%. Performance was significantly better for lipreading with electrical stimulation than for lipreading alone and for electrical stimulation alone than for lipreading alone. An information transmission analysis demonstrated the effective integration of visual and auditory information for lipreading with electrical stimulation. There was a significant improvement in performance for the electrical stimulation alone condition over the 2 months of the study in contrast to no such improvement for lipreading alone.

Cochlear Implants↗
PubMed1982

Psychophysical studies for two multiple-channel cochlear implant patients.

Psychophysical studies were conducted on two multiple-channel cochlear implant patients to examine the nature of the hearing sensations produced by electrical stimulation of auditory nerve fibers using electrodes at different sites in the scala tympani (one electrode at a time). Both time-invariant stimuli, whose parameter values did not vary in time, and time-varying stimuli, specified by a linear variation in parameter values, were used. A sharpness ranking study using time-invariant signals suggested that the hearing sensations produced by different electrodes varied from dull to sharp in an apical to basal direction in the scala tympani. A categorization study showed that the hearing sensations produced by two adjacent electrodes (1.5 mm apart) were rarely confused for a restricted range of time-invariant pulse rates. Discriminability studies by a same-different procedure for stimuli with pulse rate below 250 pps showed: (1) relative difference limens of 6% to 12% for time-invariant pulse rates, and 9% and 13% for time-varying pulse rates; (2) stimuli with time-varying electrode position differing in the direction of electrode trajectory were readily discriminated; and (3) the discrimination of time-varying pulse rates deteriorated with decreases in the duration of the variation, while the discriminability of single-electrode trajectories was the same for the three durations: 25, 50, and 100 ms. A speech processing strategy was also proposed on the bases of these results.

Auditory Perception↗
PubMedDate not supplied

Comparison of two cochlear implant speech-processing strategies.

Speech processors extracting either the fundamental frequency (F0) alone, or the fundamental frequency combined with second formant information (F0-F2), have been evaluated on a totally deaf patient using a multiple-channel cochlear implant. A closed set test using 16 spondees and a modified rhyme test showed that for electrical stimulation alone the F0-F2 speech processor was significantly better than the F0 processor. The open set tests using phonetically balanced words and Central Institute for the Deaf everyday sentences showed that for electrical stimulation alone and electrical stimulation combined with lipreading, the results with the F0-F2 speech processor were all significantly better than with the F0 processor. Information transmission for consonant speech features was also better when using the F0-F2 processor.

Cochlear Implants↗
PubMedDate not supplied

A multiple-channel cochlear implant and wearable speech-processor: an audiological evaluation.

Stand audiological tests were administered to a totally deaf multiple-channel cochlear implant patient with a wearable speech-processor in a monitored sound field under the following conditions: a wearable unit activated alone (WA), lipreading with the wearable unit off (LA), and wearable unit activated in combination with lipreading (WL). Thresholds obtained for narrow-band noise signals indicated that the wearable unit allowed the patient to detect a variety of sounds at different frequencies. The results obtained in closed-set word tests and open-set word and sentence tests showed significant improvements in word and sentence scores from LA to WL. In the open-set (C.I.D.) sentence test, the patient scored 22% for LA and 76% for WL. The WL score of 76% correlates with a satisfactory performance in understanding connected speech. The patient also scored 30% correct in a test involving the recognition of environmental sounds.

Cochlear Implants↗
PubMedDate not supplied

Perception of connected speech without lipreading, using a multi-channel hearing prosthesis.

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 words 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.

Adult↗
PubMedDate not supplied

Speech perception using a two-formant 22-electrode cochlear prosthesis in quiet and in noise.

A new speech-processing strategy has been developed for the Cochlear Pty. Ltd. 22-electrode cochlear prosthesis which codes an estimate of the first formant frequency in addition to the amplitude, voice pitch and second formant frequencies. Two groups of cochlear implant patients were tested 3 months after implant surgery, one group (n = 13) having used the old (F0F2) processing strategy and the other (n = 9) having used the new (F0F1F2) strategy. All patients underwent similar postoperative training programs. Results indicated significantly improved speech recognition for the F0F1F2 group, particularly on open set tests with audition alone. Additional testing with a smaller group of patients was carried out with competing noise (speech babble). Results for a closed set spondee test showed that patient performance was significantly degraded at a signal-to-noise ratio of 10 dB when using the F0F2 strategy, but was not significantly affected with the F0F1F2 strategy.

Adult↗
PubMedDate not supplied

Results of a preliminary clinical trial on a multiple channel cochlear prosthesis.

Speech discrimination testing was carried out under clinical trial conditions for eight profoundly postlingually deaf adults to assess the efficacy of a newly developed 22-channel cochlear prosthesis and speech processor. Three months postoperatively, these patients showed significantly better results with the cochlear prosthesis than for preoperative testing with a conventional hearing aid or vibrotactile aid (following a 6-month trial with the aid) on each of a series of tests from the Minimal Auditory Capabilities battery. Assessment of lipreading enhancement using standard speech tests, consonant recognition studies, and speech tracking showed significant improvements for each patient when using the cochlear prosthesis. Six patients showed a significant amount of open set speech discrimination without lipreading at levels which have not been reported for single electrode cochlear prostheses. The two patients who performed poorly on these tests both had restricted multiple channel systems due to their disease, one patient being restricted to virtually a single channel system and the other to only ten of the 22 electrodes. These results indicate that this multiple channel cochlear prosthesis has potential as a treatment for profound postlingual deafness over a wide range of etiologies and ages.

Adult↗