The Basics of Hearing and Hearing Loss
Summary of a talk given by Henry Lam, MSc Aud(C) RAUD RHIP (Western Institute for the Deaf and Hard of Hearing), given to the BC Balance and Dizziness Disorders Society at St. Paul’s Hospital on September 23, 2015.
Description of the auditory system
For the auditory system to function normally a sound has to travel through all three parts of the ear: Outer (external) ear through the middle to the inner (see figure 1 below). The external ear is funnel-shaped to catch sound and channel it through the ear canal to the ear drum. This causes the ear drum to vibrate, changing the sound waves into mechanical vibrations. These vibrations then make three bones (hammer, anvil, and stirrup) in the middle ear vibrate. The hammer, anvil and stirrup bones are set up to augment the vibration.
A tube (called the Eustachian tube) connects the cavity in the middle ear to the nose and throat. During a head cold, this tube can become plugged and the vibration of the ear bones is reduced.
The final ear bone (stirrup) is attached to the cochlea (looks like a snail’s shell). There are tiny hairs and fluid within the cochlea. When the stirrup vibrates against a “window” in the cochlea’s wall, the fluid moves causing the hairs to bend and sway and produce electrical signals that are sent to the brain to be interpreted.
The fluid in the cochlea is shared with the balance (semi-circular) canals. Hence hearing loss and balance impairment sometimes go together.
Types of hearing loss:
- Conductive hearing loss (outer ear)
Typical causes are eardrum perforation, earwax, growths, or abnormalities in the shape of the ear.
- Conductive hearing loss (middle ear)
Causes include middle ear fluid, ear infections, loose ear bones, otosclerosis (abnormal overgrowth of bone in the middle ear), and cholesteatoma (abnormal skin growth in the middle ear).
- Sensorineural hearing loss (inner ear)
Causes include hair cell damage resulting from presbycusis (age-related hearing loss), noise exposure, hereditary/genetic causes, ototoxic drugs, viral infections, head trauma, or result of illness such as meningitis.
How common is hearing loss?
Table 1: Percent with hearing loss by age
Hearing loss is more common than we think. It affects over half of all seniors, and about two-third of those over 85.
Common symptoms of hearing loss:
- Hearing speech but not understanding what is said
- Feeling as though most people mumble
- Difficulty hearing in the presence of background noise
- Ringing or buzzing in the ears (tinnitus)
- Continually asking people to repeat words or phrases
- Preferring the TV or radio louder than others do
- Finding some sounds abnormally loud.
Dealing with ear wax
Ear wax plays a role in keeping the ears clean by capturing dead skin and other debris that collect in the ear and slowly makes its way out. Excess wax is one of the common causes of temporary hearing loss. Some people produce too much wax which then blocks vibrations from reaching the eardrum.
Never use Q-tips or similar objects to clear the wax. Such objects fit easily into the ear and can puncture the ear drum. Use over-the-counter medications or drops of olive oil to soften the wax. If this isn’t successful, a doctor’s visit is the next step.
The most common way doctors remove wax is by using water to flush it out. If the wax has been previously softened with oil, the doctor can remove it more easily.
If you have vestibular problems, the process of removing excess wax may cause severe dizziness. A specialist may be the best option for removing the wax.
People often resist getting hearing aids and deny that they need them. Hearing aids are not a fashion statement like glasses. They cost in the range of $2000—$6000 per pair. There are many different types, and a good choice depends on your type of hearing loss, what features you want; and price.
Modern hearing aids contain a computer chip which can be sensitive to direction and frequency and can vary with changing conditions. For example, hearing aids can be made more sensitive to sound coming from the front, thus reducing background noise. They can also improve clarity (to a point) as well as increase volume.
Psychosocial effects of hearing loss
Because of the inability to hear clearly, people with hearing loss tend to withdraw from social interactions. They miss parts of conversations, resulting in confusion and frustration. Denial is common and family relationships are often strained when the sufferer ignores or misunderstands verbal communication.
The part of the brain that normally receives signals from the inner ear (auditory cortex) starts to shut down from lack of use and this can affect other parts of the brain.
Poor hearing isolates people from their social network, and has a negative effect on the brain. In conclusion, as with any other part of the body, the auditory system needs care and attention, and sometimes assistance, to carry out its mission.