Hearing loss can occur for many reasons, but a common cause is damage to the ear structures, specifically, the cochlea and its inner hair cells. Cochlear hair cell damage can happen for many reasons: exposure to loud noises, genetics, bacterial infection, injury, and natural deterioration from aging. When the hair cells are damaged, the audibility of sounds decreases. As hearing loss progresses, a person is no longer able to access specific frequencies. Contrary to popular belief, hearing loss can occur at all ages, not just the older population. Regardless of age, there are many devices that help with hearing loss. Our lab studies individuals with hearing loss who use cochlear implants and/or hearing aids.
Cochlear Implants
When the hair cells in the cochlea are damaged, they are unable to process sound vibrations. This means that information cannot be sent to the auditory nerves and beyond. When an individual experiences significant levels of hearing loss in higher frequencies or complete hearing loss, they can use cochlear implants to improve hearing.
A cochlear implant is a device that stimulates the auditory nerve through electrical signals. The cochlear implant uses a microphone and processor outside of the head to pick up sound waves. This information is converted into electric signals, which are sent to an electrode array implanted in the cochlea (Figure 7). The electrode array sends the electrical signals through the cochlea, bypassing the hair cells, activating the auditory nerve. The signals then goes to the auditory cortex, allowing the user to interpret inputs like speech.
Figure 6: Cochlear implant model and function.
Implantation: Bilateral vs. Unilateral
Bilateral implants mean that cochlear implants are placed on both sides, while unilateral means a cochlear implant is placed in only one ear. One of the main research focuses is understanding how CIs alter auditory processing. We are also interested in understanding how synchronized input through bilateral CIs can influence localization.
Hearing Aids
Hearing aids are used to amplify sound waves in the environment. It allows the ear to detect frequencies it wouldn’t be able to access without the additional gain/amplification.
While there are many kinds of Hearing Aids, they generally work the same (Figure 7)
- Sound waves are received by a set of microphones, which convert and process the sound waves into electrical signals.
- These electrical signals are then sent to an amplifier, making the sounds louder.
- The amplifier sends the sounds to your ear through the speaker, which is inserted into the ear.
- The amplified sound is then sent into the ear and through the inner and middle ear into the cochlea, allowing the hair cells to pick up the amplified sound.
Figure 7: Hearing Aid function.