Fig: The internal part of a cochlea implant Fig: Cochlea implant as worn by user
Deafness is due to following reasons:
Bony deposits in the inner ear caused by the aging process.
Auricle and the opening into the outer auditory canal may be missing at birth.
Injury to the ear cartilage followed by internal bleeding and excessive production of ear tissue (cauliflower ear).
Perforation of the eardrum may be caused by injury from a sharp object or by sudden changes in atmospheric pressure.
Damage to the organ of Corti in the inner ear accounts for the condition of many people who are either totally deaf or severely hearing impaired.
It is a big question .We have hearing aids so why patient should go through operation?
So here is the difference that we can sort out between the two:
Cochlear implants Hearing aids consonants and vowels are understandable Only vowels Unlimited possibilities for signal coding Limited signal coding Surgically implanted No surgery needed 3 batteries or charged battery 1 battery Battery life: 1 to 3 days Battery life: 1 to 2 weeks Success is individual and unpredictable Success is individual and unpredictable Rechargeable Non- rechargeable
THE EARLY YEARS:
Research during the late 18th and 19th centuries.
1. 18th century Alessandro Volta discovered Electrolytic cell.
2. In 1950 Djourno and Charles Eyries Studied using current.
3. In 1961 ,William House. He developed devices to stimulate acoustic nerves
We hear through the sound analyzing action of the cochlea (inner ear) and the auditory centers of the brain.
The mechanical-neural transducer of the hearing system is the hair cell,
The cochlear model was described by Lyon.
He combines a series of filters that model the traveling pressure waves with Half Wave Rectifiers (HWR) to detect the energy in the signal and several stages of
Fig: The cochlear model (Lyon)
Parts of the cochlear implant:
a speech processor
a receiver and stimulator
an array of up to 22 electrodes wound through the cochlea.
Fig: Floorplan of 100-stage cochlea chip,
Fig: Artist‘s conception of the cochlea Fig: Photomicrograph of 480-stage cochlea test chip.
Filter bank strategies use Fast Fourier Transforms.
Feature extraction strategies used features which are common to all vowels.
The transmitter attaches to the receiver using a magnet that holds through the skin.
It is used to transmit the processed sound information over a radio frequency .
It receives directions from the speech processor by way of magnetic induction sent from the transmitter.
receiver is also a sophisticated computer .
It is embedded in the skull behind the ear.
The electrode array is made from a type of silicone rubber.
The electrodes are platinum or a similarly highly conductive material.
The mean length of human being cochlea is 33–36 mm.
22 array electrodes within the cochlea and 2 extra-cochlear electrodes (ground).
It transforms the sounds picked up by the microphone into electronic signals .
There are primarily two forms of speech processors available
Programming the speech processor
The cochlear implant must be programmed individually for each user.
The programming is performed by an audiologist trained to work with cochlear implants.
Damage to nerve cells within the cochlea
It is not as good as the quality of sound processed by a natural cochlea.
VLSI technology limitations such as threshold variation
present an important challenge in designing systems with appropriate collective behavior.
Outer hair cells provide active and adaptive undamping to boost weak sounds and attenuate loud ones, there by providing the gain-control element of an AGC loop.
The key problems in sound perception are to cope with a very wide dynamic range of loudness and to separate sounds on the basis of their properties, such as frequency content and time structure.
The problems we must solve to build perception machines are mostly similar to those that nature had to solve biologically in the evolution of intelligent animal behavior.