Understanding Hearing Loss

Sound travels in air-conducted waves to your outer ear. The outer ear is the portion of the ear you can see. Sound is funneled into the ear canal where it strikes the eardrum causing it to vibrate. The vibrating motion of the eardrum causes a mechanical disturbance in the middle ear.

The middle ear is composed of the eardrum and three bones: the malleus, the incus and the stapes. These three bones are pushed into a rocking motion from the vibration of the eardrum. The base of the stapes transmits the motion to the inner ear disturbing tiny hair cells. The disturbance of these hair cells stimulates the auditory nerve, which then delivers a signal to the brain recognized as sound.

A hearing loss results whenever there is an interruption in the path of sound through the air to the brain. Conductive hearing losses occur when there is a problem in the outer ear or the middle ear (ex. wax or middle-ear infection). Sensorineural hearing losses occur when there is a problem in the inner ear or along the auditory nerve. Some conductive hearing losses can be corrected with medication or surgery. Sensorineural hearing losses are usually permanent.

How is hearing loss classified?

Hearing loss is ranked by degree. A mild hearing loss may cause you to miss 25-40% of the speech signal. Usually this results in problems with clarity since the brain is receiving some sounds but not all of the information. A moderate hearing loss may cause you to miss 50-75% of the speech signal. This means you would not have problems hearing at short distances, face-to-face, but would have problems if distance or visual cues changed.

A severe hearing loss may cause you to miss up to 100% of the speech signal. Someone with a severe hearing loss may hear loud voices 12 inches away from the ear. A profound hearing loss will cause you to rely on vision instead of hearing since none of the speech signal is received. More specific information about your particular hearing loss can be obtained by having a hearing evaluation from a professional who is trained in the diagnosis and rehabilitation of hearing loss (certified audiologist or licensed and certified hearing instrument specialist).

Hearing loss is characterized by ears also: unilateral (one ear) and bilateral (both ears). With a unilateral hearing loss you may have problems hearing soft speech, hearing speech in background noise and localizing (finding the source of a sound, or the direction). Bilateral hearing loss will present problems of hearing the speech signal according to the degree of the loss.

Another fact to consider when classifying a hearing loss is the location of the hearing loss across the range of speech frequencies, or pitches. There is a wide range of pitches in everyday sounds and speech. For example, the "o" sound is louder and lower in pitch than the "s" sound which is softer and higher in pitch. Usually a hearing loss does not affect all speech frequencies/pitches the same. For example, the person who has been around excessive loud noise will probably have what is termed a "high-frequency hearing loss." This type of loss affects the high pitches (treble) of sound more than the low pitches (base). This person would have difficulty with sounds that are higher in pitch (ex. female voices; children's voices; hearing speech sounds such as "s," "t;" and hearing birds). This type of hearing loss makes understanding difficult because the person hears low-pitched noise at a normal volume but misses out on a lot of speech sounds that bring clarity (high-pitched consonants).

What can you do about hearing loss?