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N Dillier

Publications and source records attributed to N Dillier.

10 recordsLinked to original sources
PubMed1992

Digital speech processing for cochlear implants.

A rather general basic working hypothesis for cochlear implant research might be formulated as follows. Signal processing for cochlear implants should carefully select a subset of the total information contained in the sound signal and transform these elements into those physical stimulation parameters which can generate distinctive perceptions for the listener. Several new digital processing strategies have thus been implemented on a laboratory cochlear implant speech processor for the Nucleus 22-electrode system. One of the approaches (PES, pitch excited sampler) is based on the maximum peak channel vocoder concept whereby the spectral energy of a number of frequency bands is transformed into appropriate electrical stimulation parameters for up to 22 electrodes using a voice pitch synchronous pulse rate at any electrode. Another approach (CIS, continuous interleaved sampler) uses a maximally high pitch-independent stimulation pulse rate on a selected number of electrodes. As only one electrode can be stimulated at any instance of time, the rate of stimulation is limited by the required stimulus pulse widths (as determined individually for each subject) and some additional constraints and parameters which have to be optimized and fine tuned by psychophysical measurements. Evaluation experiments with 5 cochlear implant users resulted in significantly improved performance in consonant identification tests with the new processing strategies as compared with the subjects own wearable speech processors whereas improvements in vowel identification tasks were rarely observed. The pitch-synchronous coding (PES) resulted in worse performance compared to the coding without explicit pitch extraction (CIS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Experimental endolymphatic hydrops: are cochlear and vestibular symptoms caused by increased endolymphatic pressure?

The correlation between inner ear pressure and cochlear function was investigated in guinea pigs with unilaterally obliterated endolymphatic sacs and ducts. In 11 animals that developed endolymphatic hydrops, auditory thresholds as monitored by auditory evoked action potentials had increased with recruitment. Most of these animals also experienced episodes of spontaneous nystagmus. In control ears endolymphatic pressure did not differ more than 0.5 cm H2O from perilymphatic pressure. In six of 11 hydropic ears, endolymphatic pressure was more than 0.5 cm H2O higher than perilympathic pressure; auditory thresholds in all these ears had deteriorated within 2 weeks before pressure recording. No further hearing deterioration within this period was noted in five hydropic ears with endolymphatic pressure equal to or lower than perilymphatic pressure. Endolympathic-perilymphatic pressure gradients may contribute to auditory threshold increase in endolymphatic hydrops, but are not its only cause.

Animals↗
PubMed1990

Comparison of hearing aids and cochlear implants in profoundly and totally deaf persons.

Cochlear implants are increasingly used in the rehabilitation of the profoundly and totally deaf. Usually, insufficient gain of speech discrimination with a powerful conventional hearing aid is considered as a prerequisite for a cochlear prosthesis. With recent improvements of electronic systems, the criterion for this decision may change. To keep pace with the technical progress, a battery of speech sound tests suited for minimal auditory capabilities (MAC-battery) was developed and applied to groups of patients fitted with conventional instruments and with two different types of cochlear implants. Based on the comparison of the MAC-battery results of hearing aid groups, with the average performance of an implanted group, most conventionally fitted regular users of hearing aids should not be considered as candidates for cochlear implantation. The MAC-battery, although not a strictly standardized procedure, is a useful instrument for patient counselling and for the selection of implant candidates.

Adolescent↗
PubMed1990

Endoneurial fluid pressure in the facial nerve of guinea pigs and rabbits.

Endoneurial fluid pressure (EFP) was measured in the facial nerve in rabbits and guinea pigs using a servo-controlled micropipette system. EFP in the tympanic segment was 5.3 +/- 1.2 cm H2O in rabbits and 4.1 +/- 0.9 and 4.2 +/- 0.9 cm H2O in the tympanic and mastoid segment respectively in guinea pigs, while EFP in the sciatic nerve was around 2 cm H2O. The higher pressure in the facial nerve may be related to the proximo-distal flow of the endoneurial fluid in peripheral nerves.

Animals↗
PubMed1990

Wearable digital speech processor for cochlear implants using a TMS320C25.

Based on a single-chip DSP (TMS320C25, Texas Instruments) a programmable battery-operated sound processor with a digital encoder interface for the Nucleus-22 cochlear implant (CI) was built. The number of quasi-simultaneously addressed electrodes is only limited by the selected pulse width and the maximum rate of stimulation and can be as high as 10 electrodes at 300 Hz repetition rate. Implementation of various processing strategies (formant or channel vocoder, filterbank, zero crossings, etc.) is possible as well as sophisticated adaptive noise reduction. Programs and stimulation parameters are stored in electrically erasable memory and may be updated via a host computer. The built-in analog output may be used for single-channel stimulation or acoustic verifications of the sound processing algorithms. The power consumption with current 16K word data memory and at maximum stimulation rate is about 1 Watt, which necessitates recharging of batteries after 11 h.

Cochlear Implants↗
PubMed1989

Comparison of single-channel extracochlear and multichannel intracochlear electrodes in the same patient.

A postlingually deaf patient who had been using a single-channel extracochlear implant for 5 years was reimplanted in the same ear with a 22-channel intracochlear device after electrical failure of the internal receiver. In the subsequent follow-up period, auditory performance was investigated in a series of tests with nonspeech and speech material. Two weeks after processor fitting most test scores were equal or better with the new implant. Three months later, with only minimal training, the patient's performance in sentence, numerals and vowel tests was markedly improved. Analysis of vowel confusion matrices indicated a high percentage of F2 information perceived (53% compared with 5% with the single-channel device) and somewhat less F1 information (35% compared with 4% using the single-channel device). Further improvements of speech discrimination (especially consonant recognition) are conceivable if the fine temporal resolution provided by some single-channel devices can be combined with the spectral resolution of multichannel systems.

Cochlear Implants↗
PubMed1988

[Perception of acoustic speech features with single channel cochlear implants and hearing aids. A comparative analysis].

A newly developed battery of 12 multiple-choice tests for the German language (graded according to difficulty) comprising identification of sentences, words and syllables was applied to 8 patients with single-channel cochlear implants and to 35 deaf hearing-aid users. Phoneme confusion matrices were analysed using sequential information transmission analysis (SINFA) and multi-dimensional scaling (SINDSCAL). Acoustic parameters of the digitally stored test items were compared with the outcome of SINFA and SINDSCAL. It was found that cochlear implant and hearing-aid users relied on the same perceptual dimensions which were correlated to acoustic signal properties of the speech sounds. Best perceived acoustic features were time and amplitude structure of the speech sound (envelope). Fundamental and first formant frequency are evaluated both by implant and hearing-aid users. The use of higher frequency spectral information depends on the amount of residual hearing.

Auditory Threshold↗
PubMed1978

Activation of an inhibitory noradrenergic pathway projecting from the locus coeruleus to the cingulate cortex of the rat.

Repetitive stimulation of the locus coeruleus evoked strong inhibition of the firing rate of about 50% of cells of the cingulate rat cortex. Forty per cent of the cells were not affected and 9% were excited by stimulation of the locus coeruleus. Pretreatment of the rats with reserpine and alpha-methyl-p-tyrosine drastically reduced the percentage of cells inhibited by locus coeruleus stimulation. The cells inhibited in response to stimulation of the locus coeruleus as well as those not inhibited were depressed by microiontophoretically applied norepinephrine. This inhibitory action of NE was observed in rats anesthetized either with urethane, chloral hydrate or with Nembutal. The transsynaptically elicited, as well as the norepinephrine elicited, depression of the cells' discharge rate was antagonized by the microiontophoretically applied beta-receptor blocking drug MJ 1999. These data suggest that the inhibitory action on cingulate cortical cells of locus coeruleus stimulation is mediated by the dorsal ascending noradrenergic pathway.

Adrenergic Fibers↗
PubMed1978

[Electrical stimulation of hearing in humans: a survey of the actual state of development of an implantable prosthesis for sensorineural deafness (author's transl)].

Recent clinical results show that electrical excitation of hearing sensations with implanted electrodes in the inner ear can be successful in suitable deaf persons. A critical literature review shows that some results have been described too vaguely and that there still exist numerous methodical and technical deficiencies. Even with multichannel stimulation, true tonotopical hearing could not be achieved. Periodicity hearing alone is not sufficient for the discrimination of one-syllable words. However, most deaf persons fitted with surgically implanted electrodes judged the new hearing sensations as being agreeable and quite useful. There seem to be no long term harmful effects of these implants upon the state of the acoustic nerve. However there are still a series of basic questions in auditory physiology pending which can only be solved through intensive collaboration of the clinical disciplines involved.

Animals↗