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M Pelizzone

Publications and source records attributed to M Pelizzone.

42 records · Page 3Linked to original sources
PubMedDate not supplied

Effects of the acoustical dynamic range on speech recognition with cochlear implants.

The amplitude compression function in a speech processor for cochlear implants maps the wide acoustical dynamic range of sounds into the smaller electrical dynamic range available on the implanted electrodes. In this study, we examined the effects of systematic variations of the acoustical dynamic range of the compression function on speech recognition with cochlear implants. Statistical measures of the amplitude distribution of speech sounds were made in each channel of a research speech processor providing more than 50 dB of input signal-to-noise ratio. Several systematic variations of the dynamic range of the compression function were implemented on this basis, and speech recognition was determined using vowel and consonant identification tests in three experienced cochlear implant users. Results demonstrated that the acoustical dynamic range of the compression function does have a significant effect on speech recognition with cochlear implants. They suggest that a dynamic range of about 45 dB is necessary for optimal speech recognition.

Acoustics↗
PubMedDate not supplied

Electrically evoked compound action potential (ECAP) of the cochlear nerve in response to pulsatile electrical stimulation of the cochlea in the rat: effects of stimulation at high rates.

Some cochlear implant patients achieve better speech recognition with pulsatile electrical stimulation presented at high rates. The present study aimed to explore, in an animal model of cochlear implants, how the excitability of the cochlear nerve is affected by pulsatile electrical stimulation delivered at high rates, of up to 1,000-2,000 pulses per second (pps). Adult rats (n=23) were implanted with two or three stimulating electrodes in the left cochlea. In four of these rats, the left cochlea was deafened by local perfusion with 1 per cent or 4 per cent neomycin solutions prior to implantation. Pulsatile stimuli consisted of 20 micros electrical pulses, delivered in trains of 200 ms duration, separated by a pause of 200 ms. The pulse rates ranged from 100 to 2,000 pps (intra-train pulse rate). Electrically evoked compound action potentials (ECAPs) of the cochlear nerve were recorded either intracochlearly or from epidural electrodes (extra-cochlearly). With increasing pulse rates, the average ECAP amplitude decreased, whereas the average ECAP latency and its variability (SD) increased. For rates above 300 pps, the amplitude of the ECAP to the individual successive pulses delivered in the train progressively decreased during the initial part of the train, corresponding to a short-term adaptation of the cochlear nerve. This effect progressively increased for pulse rates ranging from 300 to 2,000 pps. In addition, there was a phenomenon of long-term adaptation, as indicated by a decrease in the amplitude of the ECAP to the first pulse of the train, indicating that the pause of 200 ms between each train was not long enough for full recovery of the cochlear nerve. This long-term adaptation was progressively more pronounced for increasing pulse rates. To characterize further the recovery in excitability of the cochlear nerve, forward masking experiments were conducted, showing a decrease of the ECAP amplitude when the interval between the first pulse (masker) and the second pulse (probe) was shorter than 2 ms. This ECAP decrease was slow for intervals between 2 and 1 ms and then abrupt for shorter intervals. The observations described above were similar for extra- and intra-cochlear recordings and were little, if at all, affected by treatment of the cochlea with neomycin.

Animals↗
PubMedDate not supplied

[The examination of color vision using a 2 metameric equation method].

Modern anomaloscopes with four independent light channels (i.e. Besançon-Anomalometer which was presented in 1979 at the SFO Congress) allow accurate examinations of color vision. In our routine clinical examination, we use two metameric equations: the red-green Rayleigh equation and the blue-green Moreland equation. This so called Two-Equation-Method enables the diagnosis of congenital and acquired color vision defects in a precise qualitative as well as quantitative way. For both equations the goal of the examination is to measure the absolute matching range. Abnormal color vision is diagnosed if the absolute matching range is shifted and/or enlarged in one or both of the two metameric equations. In congenital colour vision deficiencies, the results are similar to those obtained with the Nagel anomaloscop. The different types of acquired defects are compared with the types of Verriest's classification. A computer controlled clinical examination of color vision, which will make the procedure simplier and shorter for the patient is actually being developed.

Color Perception↗
PubMedDate not supplied

[The progeny of the two protan and deutan families described by Franceschetti and Klein (1949, 1956), one generation later. Genealogy, color vision and genomic DNA].

The progeny of the couple of which the husband was protanope and the wife deuteranope (Franceschetti, 1949) has been examined (3 generations) in 1986 and 1987. This couple had 4 children, of which 3 sons are deutan and 1 daughter, a double carrier, is phenotypically normal. This girl, in her turn and in exemplary fashion, has 3 children: 1 daughter, being simple carrier, is phenotypically normal, 1 son is protan and 1 son deutan. The study of the genomic DNA of 3 normal subjects reveals the presence of two genes responsible for green and one gene responsible for red; the genomic DNA of a protanomalous subject shows a modification of the gene for red, while that of two deuteranopes shows absence of genes responsible for green. The descent of the second couple in which the husband was deuteranope and the wife protanope (Franceschetti and Klein, 1956) is exclusively of female sex. Therefore it comprises only phenotypically normal persons.

Chromosome Mapping↗
PubMedDate not supplied

Cortical activity evoked by a multichannel cochlear prosthesis.

We have recorded electric potentials and neuromagnetic fields evoked by electric stimulation of the auditory nerve in a totally deaf patient with an implanted multichannel prosthesis. The evoked electric responses were a vertex-negative deflection at about 70 ms after stimulus onset and a vertex-positive deflection at about 180 ms. Evoked magnetic responses coinciding with the vertex potential were found in the right hemisphere, ipsilateral to the stimulated ear. The equivalent source of these responses corresponds to activation of the right auditory cortex. In the left hemisphere, the magnetic responses were considerably smaller and less reliable. These results suggest an abnormality of the central auditory pathways in this patient. In the future, neuromagnetic recordings might be used preoperatively to forecast the effectiveness of the possible implantation.

Auditory Cortex↗