How is hearing tested?
Hearing is a major part of everyday life and hearing problems are easy to test for. Hearing test results indicate the type and severity of a hearing loss. There are different types of hearing tests available, depending upon age. Behavioral testing is conducted in a sound proof room by a specially trained clinician, the audiologist, using a machine, the audiometer. The audiologist will measure the amount of hearing loss that a person has, if any. The basic hearing test is performed to determine the softest sounds a person can hear at different pitches, or frequencies. In addition, the audiologist will test word understanding, which is critical to useful hearing. These hearing tests are conducted by an audiologist while the patient sits in a sound-treated booth wearing headphones covering the ears or using small inserts in the ear.
Hearing tests results are shown in what is called an audiogram. An audiogram has two parts. The first is a graph, a picture of how well sounds are heard. The second is a percentage number that expresses the ability to understand words, when sounds are loud.
The audiogram graph shows two things: Intensity and frequency. Intensity (loudness) is measured in decibels (dB). Loudness levels are located along the lines on the audiogram that are drawn up and down. Intensities usually go from 0 dB to 125 dB; with 0 dB being very quiet and 125 dB being very, very loud. Frequency, which is another word for pitch, is measured in Hertz (Hz). The different pitches are found along the lines drawn left to right on the audiogram. We measure pitches from 125 Hz to 8000 Hz. 125 Hz is a very low pitched sound and 8000 Hz is a very high pitched sound.
The range of the hearing impairment is determined by the hearing tests. Normal hearing for sounds is between 0 and 25 decibels at all frequencies. Normally, both ears hear the same. Normal word understanding is between 88 and 100 percent. People with hearing impairments differ in the range of sounds that are most affected by the hearing loss. Some people have a high-frequency hearing loss, some others have low frequency hearing loss, and others have hearing loss across the frequency range. The degree of hearing loss can range from slight to profound. Some people have good ability to hear a sound, but can not understand words.
With some modifications, hearing tests may be performed on people of all ages. Younger children, who will not respond or cooperate with the usual hearing testing techniques (behavioral testing), can be tested with special computers (electrophysiologic testing). These computer tests can give a very close approximation of hearing level. The most commonly used electrophysiologic test is called an auditory brainstem response test, or ABR (BAER, EABR). Otoacoustic emissions are often used as a screening test in children, particularly for newborn screening, just after birth, in the hospital.