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Biomedical subjects

Y C Tong

Publications and source records attributed to Y C Tong.

At least 91 records · Page 5Linked to original sources
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↗
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↗
PubMed1981

A multiple-channel cochlear implant. Evaluation using speech tracking.

Two totally deaf patients who had received multiple-channel cochlear implants were tested using a speech "tracking" procedure in which they had to repeat verbatim passages of connected discourse. Their performance was assessed by calculating the tracking rate (words per minute) each session. Testing was carried out under two conditions--lipreading alone and lipreading in conjunction with a multiple-channel cochlear implant and laboratory speech processor. Lipreading with the cochlear implant increased the tracking rates by a factor of four for one patient and by a factor of two for the other when compared with lipreading alone.

Cochlear Implants↗
PubMed1981

A multiple-channel cochlear implant: an evaluation using open-set CID sentences.

A multiple-channel cochlear implant and speech processor have been used in two postlingually deaf adult patients with a total hearing loss, to enable them to perceive varying degrees of running speech. The results have veen confirmed with open-set CID everyday sentence tests. Using the implant alone, the patients obtained 8% and 14% scores with prerecorded material, and 34% and 36% scores for "live" presentations. This was equivalent to the perception of 35% of connected discourse. When the implant was used in conjuction with lipreading, improvements of 188% and 386% were obtained over lipreading alone, and the scores were 68% and 98% which were equivalent to the perception of 60% and 95% of connected discourse.

Adult↗
PubMed1977

A multiple-electrode hearing prosthesis for cochlea implantation in deaf patients.

A multiple-electrode hearing prosthesis for cochlea implantation in deaf patients has been developed at the University of Melbourne. It has been designed as a multiple-electrode implant to provide the best chance of enabling patients to understand speech. It has been shown that an electrode array can be threaded along the coills of the inner ear close to residual auditory nerves. Experimental studies have indicated that the long-term implantation of the array will not lead to significant degeneration of auditory nerve fibres. Loss of platinum from the stimulating electrodes can be minimized with a biphasic constant current pulse, where the first phase is negative with respect to ground. The receiver-stimulator component has also been designed to provide 10-15 channels of stimulation. Furthermore, the phase and amplitude of the stimuli to individual electrodes can be varied to enable the localization of the electrical fields to discrete groups of nerve fibres, and the correct method of frequency and intensity coding to be determined. Finally, the device should be used in the first instance for a specially selected group of adults who are post-lingually deaf.

Animals↗
PubMed1977

The clinical assessment of cochlear implant patients.

This study outlines the clinical assessment procedures adopted in the Department of Otolaryngology at the University of Melbourne for patients being considered for a cochlear implant. As the procedure is new and requires rigorous evaluation, it is considered preferable only to operate on a limited number of patients, and ensure that they have a thorough evaluation both before and after surgery. This should be carried out by a team whose members have experience in otology, audiology, aural rehabilitation, acoustics and psychology. The indications and contraindications for surgery are also outlined.

Audiometry↗
PubMed1977

A multiple electrode cochlear implant.

The University of Melbourne Departments of Otolaryngology and Electrical Engineering (UMDOLEE) receiving and stimulating component of a multiple-electrode cochlear implant hearing prosthesis produces constant stimulation. It has a stimulating pulse shape that minimizes the production of toxic substances and loss of metal from the electrodes, and this is achieved with a biphasic rectangular waveform where the first phase is negative with respect to ground. The duration of each stimulus phase in 180 msec, which is long enough to allow low levels of current stimulation, and short enough to permit rates of 1000 pulses/second to be achieved. In order to be consistent with our present understanding of the perception of pitch, the device permits the independent stimulation of a number of electrodes. Furthermore, to electrically isolate the stimulus to small areas, there is the capacity to vary the current and set the threshold independently at individual electrodes. The phase and amplitude of the pulses to neighbouring electrodes with also be varied to assist in localizing the current flow. The pattern to stimulation to individual or groups of electrodes can also be altered to enable studies to be carried out to determine ways of conveying frequency and intensity information over a more normal dynamic range.

Animals↗
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↗