Cochlear implants can bring the experience of sound to those with hearing loss, but results may vary – here’s why
Cochlear implants are among the most successful neural prostheses on the market. These artificial ears have allowed nearly 1 million people globally with severe to profound hearing loss to either regain access to the sounds around them or experience the sense of hearing for the first time.
However, the effectiveness of cochlear implants varies greatly across users because of a range of factors, such as hearing loss duration and age at implantation. Children who receive implants at a younger age may may be able to acquire auditory skills similar to their peers with natural hearing.
In fully-functional hearing, sound waves enter the ear canal and are converted into neural impulses as they move through hairlike sensory cells in the cochlea, or inner ear. These neural signals then travel through the auditory nerve behind the cochlea to the central auditory areas of the brain, resulting in a perception of sound.
People with severe to profound hearing loss often have damaged or missing sensory cells and are unable to convert sound waves into electrical signals. Cochlear implants bypass these hairlike cells by directly stimulating the auditory nerve with electrical pulses.
Cochlear implants consist of an external part wrapped behind the ear and an internal part implanted under the skin.
The external unit, which includes a microphone, signal processor and transmitter, picks up and processes sound waves from the environment. It divides sounds into different frequency bands, which are like different channels on a radio, with each band representing a specific range of frequencies within an overall spectrum of sound. It also extracts information about amplitude, or loudness, from each frequency band.
It then transmits that information to the receiver in the internal unit implanted in the cochlea. The electrodes of the internal unit directly stimulate the auditory nerve with electrical pulses based on amplitude information. Electrodes at the base of the cochlea transmit electrical signals containing high-frequency auditory information while electrodes at the top transmit electrical signals containing low-frequency information to the brain, mimicking the frequency analysis in a fully-functioning ear.