Audiological Testing Services

By Mayo Clinic Staff

How do we hear?
How do I know I have hearing loss?
Causes of hearing loss
Types of hearing loss

Several tests may be performed to discover the nature of a hearing difficulty. The test results help determine the treatment options available to patients with hearing impairment or balance and dizziness problems.

Several diagnostic evaluations are available. Tests are done based on the patient's needs. The tests include:

Basic audiogram: determines the patient's hearing ability relative to normal adult hearing levels to determine if there is a hearing loss, where it occurs and its type or classification. This information is critical to determine if medical or surgical intervention is possible or if hearing aids may help. Enhanced communication strategies may also be discussed during this session.

Tympanometry: assesses the operational status of the middle ear, which consists of the eardrum and three small bones that connect the eardrum to the inner ear. Middle-ear blockages or malfunctions often can be treated medically or surgically.

Stapedial reflexes and reflex decay: also evaluates the auditory nerve's ability to transmit hearing signals to the brain. Blockages along this pathway would indicate the need for further medical consultation.

Auditory brain-stem response (ABR) testing: Electrical nerve impulses that carry the sound from the inner ear to the brain are measured. Electrodes are placed in the ear canal and on the head, and short clicking sounds are turned on. The audiologist can determine how sound is transmitted to the brain and if there are any blockages or interruptions to the nerve impulses.

TEN (threshold equalizing noise) test: This test determines if a patient has any pitch regions in the inner ear that no longer have the ability to respond to sound stimulation, thus creating "dead zones." Information about any nonfunctional regions of the inner ear can be helpful to determine how to adjust hearing aids and how much help they can provide.

SIN (sentence-in-noise) test: evaluates the ability to understand conversational speech in noise and compare one's performance to that of normal listeners. Helps determine possible benefit from hearing aid use in noisy situations and what type of hearing aid circuitry might be needed.

Otoacoustic emissions: evaluates the functioning of the outer hair cells in the inner ear. Otoacoustic emissions are acoustic signals generated by the normal inner ear, either in the absence of acoustic stimulation (spontaneous emissions) or in response to acoustic stimulation (acoustically-evoked emissions). These emissions can be measured by placing a microphone in the opening of the ear canal and analyzing the signals obtained.


How do we hear?

Better understanding of hearing and hearing loss begins by understanding how we hear.

Sound waves are collected by the outer ear and channeled along the ear canal to the eardrum. When sound hits the eardrum, the impact creates vibrations that cause three bones in the middle ear to move. The smallest of these bones, the stapes, fits into the oval window between the middle and inner ear. When the oval window vibrates, fluid in the inner ear transmits the vibrations into the hearing organ, called the cochlea.

In the inner ear, thousands of microscopic hair cells are bent by the wavelike action of fluid inside the cochlea. The bending of these hairs sets off nerve impulses that are then passed through the auditory nerve to the hearing center of the brain. This center translates the impulses into sounds the brain can recognize.

How do I know I have hearing loss?

Hearing loss is usually gradual, developing over a long time. At some point, the hearing deterioration starts to interfere with conversational speech.

If you answer "yes" to many of the following questions, you may have hearing loss:

  • Do you ask others to repeat a lot?
  • Do people mumble more than they used to?
  • Do you need to turn the TV volume louder than people around you?
  • Do you have difficulty listening in a noisy setting?
  • Do your family and friends comment on your inability to hear?
  • Do family members tell you that you talk loudly?

Causes of hearing loss

Age: Advancing age is the most common cause of hearing loss.

Disease: Meningitis, Meniere's Syndrome, benign growths and tumors on the hearing nerve. Viral infections such as mumps and measles.

Drugs: Some drugs and antibiotics can cause damage to hair cells in the inner ear and the auditory nerve. Some of these drugs include, but are not limited too, quinine, aminoglycosides, diuretics and aspirin in large dosages.

Infections: Otitis media is a middle-ear infection characterized by the formation of fluid in the middle ear. This can be caused by allergies, head colds, inflamed tonsils and adenoids, blocked eustachian tubes, sore throats and other viruses.

Malformation: A malformation of the ear canal can sometimes cause a hearing loss.

Noise: Noise exposure (hunting, factory/plant noise, engine noise) can cause permanent hearing loss.

Perforation: Perforation of the eardrum can be caused by a change in air pressure associated with flying or scuba diving, a foreign object such as a cotton swab used to clean the ears, or pressure caused by a middle-ear infection.

Wax: Wax can build up in the ear canal and cause a blockage, stopping sound from passing through the ear canal. A physician, nurse or audiologist can periodically remove the ear wax. (Cotton swabs or sharp objects should never be used to clean the ears because they can push the wax deeper into the ear and may puncture the eardrum).

Types of hearing loss

Sensory hearing loss: occurs when the inner ear is damaged. The most common causes are aging, inner-ear infection and noise exposure. This type of hearing loss is usually not medically or surgically treatable. Most people with a sensory hearing loss find that hearing aids are beneficial.

Neural hearing loss: occurs when there is damage to the hearing nerve or the nervous system. The inner ear generates neural impulses that travel through the hearing nerve to the brain. Aging can cause degeneration of the hearing nerves. Hearing aids may help. Another cause is a tumor that presses on the hearing nerve.

Conductive hearing loss: occurs when the outer or middle ear fails to work properly. Sounds become "blocked" and are not carried to the inner ear. Conductive hearing losses are often treatable with medicine or surgery. Common causes are fluid behind the eardrum or wax buildup in the ear canal. Conductive hearing loss also can occur when the eardrum or bones of the middle ear are disrupted. Normally, when fluid builds up, it drains through the eustachian tube, which opens to the throat. The eustachian tube is normally opened by swallowing, yawning and chewing. An inflammation of the tube may keep it closed, causing fluid to build up in the middle ear. This is often the result of an upper respiratory infection and can usually can be corrected.