How We Hear

Better understanding of hearing loss begins by understanding how we hear, and knowing more about how your ear works can help you decide how well you will benefit from wearing hearing instruments. Sound waves are collected by the outer ear and channeled along the ear canal to the eardrum. When the sound waves reach the eardrum, the impact creates vibrations, which are transferred through a series of three tiny bones called malleus, incus and stapes, collectively called the ossicles. The ossicles vibrate the oval window of the inner ear which is housed in the cochlea. The cochlea is lined with hair cells. Fluid moves inside the cochlea and stimulates the hair cells. This motion is converted into electrochemical activity, activating the auditory nerve. From that point, we begin to hear and interpret sounds.

The purpose of audiological assessment is to quantify and qualify hearing in terms of the degree of hearing loss, the type of hearing loss and the configuration of the hearing loss.

The audiologist will conduct tests of hearing tones. This is called pure-tone audiometry. The results are recorded on a graph called an audiogram. The audiologist will also determine speech reception threshold or the faintest speech that can be heard half the time. Then the audiologist will determine word recognition or ability to recognize words at a comfortable loudness level.

Once the level of assessment is determined, the audiologist will conduct a physical examination. The audiologist will look at the outer ear (the pinna) checking for any misformation. The audiologist will use an otoscope, an instrument that contains a light and a magnifying lens, to examine the ear canal and eardrum. The ear canal is examined for the presence of excessive wax (cerumen), or foreign objects (food, toys, pieces of cotton swabs, etc). The eardrum (tympanic membrane) is examined for any perforation and signs of fluid or infection. The audiologist will look for any indicators suggesting the need for referral for a medical evaluation and/or treatment.

The Diagnosis tests at which we conduct are explained below:

TEST OF HEARING & LISTENING

The audiologist will conduct tests of hearing tones. This is called pure-tone audiometry. The results are recorded on a graph called an audiogram. The audiologist will also determine speech reception threshold or the faintest speech that can be heard half the time. Then the audiologist will determine word recognition or ability to recognize words at a comfortable loudness level. Testing can be modified for infants and toddlers.

TESTS OF MIDDLE EAR FUNCTION

The audiologist may also take measurements that will provide information about the status of the outer and middle ear. These are called acoustic immittance measures. Tympanometry, one aspect of immittance testing, can assist in the detection of fluid in the middle ear, perforation of the eardrum, or wax blocking the ear canal. Acoustic reflex and decay measurement, another aspect of immittance testing, can add diagnostic information about middle ear function and hearing loss.

OTOACOUSTIC EMISSIONS (OAE)

Otoacoustic emissions (OAE) are inaudible sounds emitted by the cochlea when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate. The vibration produces an inaudible sound that echoes back into the middle ear. The sound can be measured with a small probe inserted into the ear canal. Persons with normal hearing produce emissions. Those with hearing loss greater than 25-30 dB do not.

Information Links:

• Better Hearing Institute
• Educational Audiology Association
• American Academy of Audiology
• American Speech Language Hearing Association