How Do We Hear?


Ear & Hearing

Your ear has three parts, each with a different purpose. The outer ear collects sound and funnels it to the middle ear. There the sound is amplified (made louder) and sent to the inner ear, where it is converted into nerve impulses (signals) that go to the brain. The brain compares the loudness of incoming signals from each ear to determine the direction of the sound.

  • External Ear - collects and concentrates sound energy.
  • Ear Canal - carries sound to the eardrum, a membrane separating the canal and the middle ear.
  • Eardrum - vibrates in response to changes in sound energy, setting into motion three tiny bones.
  • Middle Ear Bones - three tiny bones vibrate against the fluid-filled cochlea, transmitting the sound energy into the fluid.
  • Cochlea - inside the cochlea, special nerve cells pick up the sound waves in the fluid and generate nerve impulses.
  • Auditory (hearing) Nerve - carries nerve impulses from the cochlea to the brain, where they are received and heard as sound.

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Hearing Loss

 

Types of Hearing Loss

Hearing loss can be categorized by which part of the auditory system is damaged. The three basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.

Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction of sound and causes the inability to hear soft sounds. Often this type of hearing loss can be corrected medically or surgically. Examples of conditions which may cause a conductive hearing loss include:

Sensorineural Hearing Loss

Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear) to the brain. This type of hearing loss cannot be medically or surgically corrected. It is a permanent hearing loss. Often this type of hearing loss not only involves a reduction of sound and the inability to hear soft sounds, but also affects speech understanding, or ability to hear clearly. Examples of conditions causing sensorineural hearing loss include:

  • Normal aging process (presbycusis)
  • Noise exposure
  • Viruses
  • Head trauma
  • Tumors
  • Genetic conditions

Mixed Hearing Loss

In some cases a conductive hearing loss occurs in combination with a sensorineural hearing loss. In these cases there may be damage in the outer or middle ear and the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss. View Video

Degree of Hearing Loss

Degree of hearing loss refers to the severity of the loss. There are usually five categories typically used to describe the severity of hearing loss. The numbers are representative of the patient’s thresholds, or the softest level that sound is heard:

  • Normal = 0 dB to 20 dB
  • Mild loss = 20 dB to 40 dB
  • Moderate loss = 40 dB to 60 dB
  • Severe loss = 60 dB to 80 dB
  • Profound loss = 80 dB or greater

Configuration of Hearing Loss

The configuration or shape of the hearing loss refers to the extent of hearing loss at each frequency. A hearing loss that only affects the high frequencies would be described as a high frequency loss. This configuration would indicate good low frequency hearing and poor hearing in the high frequencies. Conversely if only the low frequencies are affected the hearing loss would be described as a low frequency loss. This would indicate good hearing for the high frequency tones and poor hearing for the low frequencies. A flat hearing loss would exist when all frequencies are affected equally.

Bilateral versus Unilateral

Bilateral hearing loss indicates that both ears are involved. Unilateral hearing loss means only one ear is affected.

Symmetrical versus Asymmetrical

Symmetrical hearing loss means that the degree and configuration of the loss is the same for both ears. Asymmetrical hearing loss is one in which the degree and/or configuration of the loss is different for each ear.

Progressive versus Sudden

Progressive hearing loss is a hearing loss that becomes increasingly worse over time. A sudden hearing loss is one that has a rapid onset, occurring quickly and requiring immediate medical attention to determine its cause and treatment.

Fluctuating versus Stable

Some hearing losses change-sometimes getting better, sometimes getting worse. Fluctuating hearing loss is typically a symptom of conductive hearing loss, but can present in other conditions such as Meniere’s disease.

Today over 40 million people in the United States suffer from some degree of hearing loss. That makes hearing loss one of the most prevalent chronic healthcare problems in our society. In fact, if you are over 65 and do not have a hearing loss, you are in the minority. However, hearing loss is not restricted to the over 65 age group. Approximately 24,000 children are born with hearing impairment each year in the United States. Disease, noise exposure, and genetics can cause hearing problems no matter what your age is.


Hearing Test

Audiogram is a graph showing the results of your hearing test. Low pitch or frequencies (tones) are shown on the left and high frequencies on the right. Soft sounds are at the top of the graph and loud sounds at the bottom. The loudness where you first hear a tone is marked and these points are connected to form a line. Normal hearing levels start between 0 and 20 decibels.

How do I know if I need a hearing test?

Ask yourself these questions:

  1. Do you find yourself asking others to repeat themselves?
  2. Do people seem to mumble more often, making it hard for you to understand them?
  3. Do you have problems understanding women’s or children’s voices?
  4. Do you have difficulty following conversation while riding in a car?
  5. Do you find yourself turning up the volume on the TV, radio or stereo?
  6. Do you find it difficult to follow conversation in crowded rooms?
  7. Do you want – or need – to sit closer to the front in church, theaters, or auditoriums?
  8. Do you sometime discover that during normal conversation, you have raised your speaking voice, and seem to be almost shouting?

If you answered yes to any of these questions, you should see an audiologist for a hearing evaluation. The audiologist is an expert in hearing testing, and hearing aids, and can accurately help you find answers. This may be in the form of hearing aids, or a referral to an Ear, Nose, and Throat physician.

How do I know if my child needs a hearing test?

Off course infants and young children can not answer the above questions. They must rely on a parent/caregiver to ask themselves these questions.

  1. Is there a family history of hereditary childhood sensorineural hearing loss?
  2. Do you have concerns about a hearing, speech, language, or developmental delay?
  3. Has your child had or been exposed to any of the following: bacterial meningitis, syphilis, herpes, CMV, low birthweight (less than 3.3 lb.), ototoxic medications?
  4. View Video

Again, if you can answer yes to any of these questions, your child should receive an auditory evaluation. With today's technology, an audiologist can determine if a hearing loss is present even in newborns. Early detection of hearing loss is very important in allowing a child to develop speech and oral language. In the U.S. the average age of detection is 2.5 years. The critical period for oral speech and language development is the first 3 years. Oral speech and language can not develop normally without adequate hearing. Because of this, most experts recommend that all infants receive an auditory evaluation before 6 months of age.

The audiologist may use several tests to find which tones, sounds, and words you can and cannot hear. These tests are usually given in a soundproof room using electronic equipment. The tests are not painful or difficult to do. You are asked to signal when you hear tones and sounds that come through the earphones. Other tests will show if you can tell the difference between words that sound much alike such as fin, pin, tin, and thin.

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