Biomedical subjects

N Alcaras

Publications and source records attributed to N Alcaras.

4 recordsLinked to original sources

PubMed1984

Psychophysics of 12 channels implant.

A battery of psychophysic tests has been designed through a computerized command of the patient's emitter. Because of the fatigability of these implanted patients, especially in the case of deaf-mute children, and the tedious aspect of these exams only 4 tests are commonly used: the threshold level in a Békésy way, the tone decay test, the 2 channels discrimination at different intensity levels, the lowest intensity discrimination. If the electrode impedances have been per-operatively measured, these tests are useful to understand the particular phonemic discrimination difficulties of each patient.

Auditory Perception↗

PubMed1984

Description of the French 12 channel cochlear implant.

The sound information is sequentially transmitted to 12 electrodes implanted in the cochlea. An electrode bearer introduced through the round window is now commonly used. Frequencies between 100-4 000 Hz and intensities between 40-100 db are only transmitted in a 3 msec time sampling. The output signal is a positive square wave followed by an equal negative wave. Its voltage varies from 2.5 to 6.5 volts. Its duration varies from 0 to 200 microsec. Its frequency is equal or inferior to 300 Hz. The outside emitter weighs 600 g. This system has been implanted in 58 patients and allows partial speech discrimination without lipreading for more than 6 years.

Action Potentials↗

PubMed1984

Sound signal processing.

In the CHORIMAC-12, the French device, the whole speech information despite its redundancy is transmitted to the few cochlear nerve fibers that are still present. Only loud speech intensities between 40 db and 100 db are introduced in a filter battery which gives out the frequency information in 12 channels including the 100-6000 Hz. This 60 db intensity scale is transmitted in a compression rate of about 6 db. The time sampling is 3 msec. A 12 electrode bearer or 12 separate electrodes (in case of ossified cochlea) transmit the electrical information. The electrical stimulus is a square wave: its frequency is equal or inferior to 300 Hz; its voltage may vary between 2.5 and 6.5 volts; its duration may vary between 0 and 200 mu sec. The performances of the system is demonstrated by means of a system of computerized psychophysic tests and speech intelligibility tests.

Cochlear Implants↗

PubMedDate not supplied

Study of the mechanism of vocal fold vibration during phonation.

The precise mechanism of vocal fold vibrations during phonation is not well known. At present it is impossible to say whether this movement is active or passive. Since the studies of MacLeod & Louis Sylvestre, we know that the vocal muscle is asynchronous and, so, can have a fast oscillatory movement induced by a continuous depolarization of the muscular fibre membranes. Thus, we believe at present that the glottic opening can be merely passive and that the closing can be both passive and active through a myogenic mechanism. The purpose of this work was to try to establish whether this concept is right, by recording simultaneously the aerodynamic forces acting upon the vocal folds and their acceleration during phonation. This acceleration represents the forces applied to the vocal folds as a function of time. By comparing the temporal evolution of the two forces we can assert that glottic opening is a passive movement. This protocol does not allow us to know if closure is due solely to the elastic retractive force, or also to a muscular, active force such as myogenic rhythm. To answer this question we must use another protocol.

Acceleration↗