A variety of tests can be used to identify and diagnose a hearing loss. The method used depends in part on the age of the individual and other factors.
Pure Tone TEsting
A pure-tone air conduction hearing test determines the faintest tones a person can hear at selected pitches (frequencies), from low to high. During this test, earphones are worn so that information can be obtained for each ear.
Sometimes, use of earphones for the test is not possible, such as when a child refuses to wear them. In these cases, sounds are presented through speakers inside a sound booth (called sound-field screening). Since sound-field screening does not give ear-specific information, a unilateral hearing loss (hearing loss in only one ear) may be missed.
The person taking the test may be asked to respond to the sounds in a variety of ways, such as by:
- Raising a finger or hand
- Pressing a button, pointing to the ear where the sound was received
- Saying "yes" to indicate that the sound was heard
The results are recorded in an audiogram.
Sometimes, young children are given a more play-like activity to indicate response. The most common techniques involve visual reinforcement audiometry (VRA) and conditioned play audiometry (CPA).
Visual reinforcement audiometry is the method of choice for screening children between 6 months and 2 years of age. The child is trained to look toward a sound source. When the child gives a correct response (e.g., looking to a source of sound when it is presented), the child is "rewarded" through a visual reinforcement. Example rewards include getting to watch a toy that moves or a flashing light.
Conditioned play audiometry can be used as the child matures and is commonly used with toddlers and preschoolers (ages 2–5). The child is trained to perform an activity each time a sound is heard. The activity may involve putting a block in a box, placing pegs in a hole, or putting a ring on a cone.
If there is a blockage, such as wax or fluid, in the outer or middle ears, a method called pure- tone bone conduction testing may be used. With this technique, the blockage is bypassed by sending a tone through a small vibrator placed behind the ear (or on the forehead). The signal reaches the inner ear (or cochlea) directly through gentle vibrations of the skull. This testing can measure response of the inner ear to sound independently of the outer and middle ears. In these cases, this test helps the audiologist determine the type of hearing loss being measured.
The audiologist will also conduct tests of listening and speech. These results are also recorded on the audiogram. One test that the audiologist conducts during a hearing test is the speech reception threshold (SRT). This is used with older children and adults, and helps to confirm the pure-tone test results. The SRT records the faintest speech that can be heard half the time. Then the audiologist will also record word recognition or the ability to correctly repeat back words at a comfortable loudness level.
Speech testing may be done in a quiet or noisy environment. Difficulty understanding speech in background noise is a common complaint of people with hearing loss, and this information is helpful.
Tests of the Middle Ear
The audiologist may also take measurements that will provide information about how the middle ear is functioning. These measurements include tympanometry, acoustic reflex measures, and static acoustic measures. This type of testing is particularly important in preschool children (ages 3–5), for whom hearing loss is more often associated with middle ear disease.
Tympanometry assists in the detection of fluid in the middle ear, perforation of the eardrum, or wax blocking the ear canal. Tympanometry pushes air pressure into the ear canal, making the eardrum move back and forth. The test measures the mobility of the eardrum. Graphs are created, called tympanograms. These can reveal a stiff eardrum, a hole in the eardrum, or an eardrum that moves too much. The tympanogram is often recorded when children have middle ear infections.
Acoustic reflex measures add information about the possible location of the hearing problem. Everyone has an acoustic reflex to sounds. A tiny muscle in the middle ear contracts when a loud sound occurs. The loudness level at which the acoustic reflex occurs—or the absence of the acoustic reflex—gives information to the audiologist about the type of hearing loss.
Static acoustic impedance measures the physical volume of air in the ear canal. This test is useful in identifying a perforated eardrum or checking the openness of ventilation tubes.
Auditory Brainstem Response (ABR)
The auditory brainstem response (ABR) test gives information about the inner ear (cochlea) and brain pathways for hearing. This test is also sometimes referred to as auditory evoked potential (AEP). The test can be used with children or others who have a difficult time with conventional behavioral methods of hearing screening. The ABR is also indicated for a person with signs, symptoms, or complaints suggesting a type of hearing loss in the brain or a brain pathway.
The ABR is performed by pasting electrodes on the head—similar to electrodes placed around the heart when an electrocardiogram is run—and recording brain wave activity in response to sound. The person being tested rests quietly or sleeps while the test is performed. No response is necessary. ABR can also be used as a screening test in newborn hearing screening programs. When used as a screening test, only one intensity or loudness level is checked, and the baby either passes or fails the screen.
Otoacoustic Emissions (OAE)
Otoacoustic emissions (OAEs) are sounds given off by the inner ear when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate. The vibration produces a nearly inaudible sound that echoes back into the middle ear. The sound can be measured with a small probe inserted into the ear canal.
People with normal hearing produce emissions. Those with hearing loss greater than 25–30 decibels (dB) do not produce these very soft sounds. The OAE test is often part of a newborn hearing screening program. This test can detect blockage in the outer ear canal, as well as the presence of middle ear fluid and damage to the outer hair cells in the cochlea.
After the test battery is completed, the audiologist will review with you each component of the audiologic evaluation to obtain a profile of hearing abilities and needs. Additional specialized testing may be indicated and recommended based on these initial test results. The hearing evaluation may result in recommendations related to:
- Further follow-up such as medical referral
- Educational referral
- Hearing aid/sensory aid assessment
- Assessment for assistive listening devices
- Hearing rehabilitation assessment
- Speech and language assessment and/or counseling
As you can see, an audiologic evaluation is much more than “just a hearing test!”