Presented by The Audiology Awareness Campaign
This article will describe tests commonly included in a basic audiologic (hearing) evaluation. These tests are typically performed in a sound treated room or booth. Additional tests may be required depending on the history, the complaint or to clarify site of lesion or for selection of hearing aids. Those additional tests will be discussed in articles that deal with each of those topics.
Tone threshold tests identify the weakest level that can be heard for each test frequency (pitch). Low frequencies are designated by lower numbers and high frequencies are represented by the higher numbers. Typically, the frequency range is "sampled" at octave intervals between 250 and 8000 Hz.
Tone tests are done by air conduction and by bone conduction. Air conduction tests evaluate the sensitivity of the entire hearing organ and are tested with earphones that are placed over the ears or inserted into the ear canal. The audiologist presents single frequency ("pure") tones produced by a calibrated audiometer. The softest sounds heard by the subject at each pitch are recorded as the thresholds and are compared to normative values. Bone conduction is tested when air conduction testing shows a loss. They are done as in air conduction testing, except that, instead of using earphones, a small bone-conduction vibrator is placed on the mastoid bone directly behind the ear and sound is transmitted through the bones of the skull directly to the inner ear, bypassing the outer and middle ear. Thus, a difference between air and bone conduction thresholds indicates a loss caused by a problem with the outer or middle ear-a "conductive" loss.
Speech Recognition Threshold
The purpose of this test is to determine the patient's threshold for two-syllable words like "baseball, " "cowboy," etc. Threshold is the faintest intensity that the words can be correctly repeated at least 50% of the time.
Word Recognition Score
This test determines the subject's ability to correctly repeat single syllable words presented at a comfortable intensity. A list of words is presented and the patient repeats the words back. This test reflects how clearly or distinctly words are understood.
Impedance/Admittance Test (Tympanometry)
This test shows how efficiently the middle ear is working. The Audiologist places a small probe into the patient's ear canal that will seal it closed. A small pump will vary the pressure slightly and the instrument measures the middle ear's ability to transmit sound to the inner ear. The canal pressure at the point where the sound is most easily transferred matches the middle ear pressure. In a normal ear, that will be atmospheric air pressure. Different middle ear conditions result in different kinds of admittance patterns, so the test is helpful in delineating the type of middle ear problem, if any.
Acoustic Reflex Test
Loud sound triggers a contraction of the tiny muscles in the middle ear, stiffening the ossicular chain so that less sound is passed through the middle ear. This test gives the audiologist information about the function of the inner ear, the auditory nerve up to the brainstem level and the function of the facial nerve.
*This article was submitted by:
Glen R. Meier, M.S., CCC-A, FAAA and subsequently edited by AAC.