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.
With regard to degree of hearing loss, the audiologist is looking for quantitative information. Hearing levels are expressed in decibels (dB) based on the pure tone average for the frequencies 500 to 4000 Hz and discussed using descriptors related to severity: normal hearing (0 to 20 dB HL), mild hearing loss (20-40 dB HL), moderate hearing loss (40-60 dB HL), severe (60-80 dB HL) and profound hearing loss (80 dB HL or greater).
With regard to the type of hearing loss, the audiologist is looking for information that suggests the point in the auditory system where the loss is occurring. The loss may be conductive (a temporary or permanent hearing loss typically due to abnormal conditions of the outer and/or middle ear), sensorineural (typically a permanent hearing loss due to disease, trauma, or inherited conditions affecting the nerve cells in the cochlea, the inner ear, or the eighth cranial nerve), mixed (a combination of conductive and sensorineural components), or a central auditory processing disorder (a condition where the brain has difficulty processing auditory signals that are heard).
With regard to the configuration of the hearing loss, the audiologist is looking at qualitative attributes such as bilateral versus unilateral hearing loss; symmetrical versus asymmetrical hearing loss; high-frequency versus low frequency hearing loss; flat versus sloping versus precipitous hearing loss; progressive versus sudden hearing loss; and stable versus fluctuating hearing loss.
Audiological evaluation is also carried out for purposes of monitoring an already identified hearing loss. Once a particular hearing loss has been identified, a treatment and management plan is put into place. The plan may include medical or surgical intervention, prescription of personal hearing aids, prescription/provision of assistive listening devices, skills development through aural (audiologic) habilitation/rehabilitation, or simply monitoring of the condition through periodic assessment.
Once a treatment and management plan is in place, it is still important for an individual’s hearing loss to be checked periodically to determine its stability. Is it fluctuating? Has it improved as a result of medical intervention? Is it progressing? Have new conditions come into play that have affected the original condition? It is also important that a person’s ability to hear using amplification (e.g., personal hearing aids and any assistive listening devices that are used in place of, or in conjunction with, personal amplification) be monitored and documented. This monitoring would include functional gain assessment, real ear measurement, electroacoustic analysis, listening check, and even informal “functional” assessment in the person’s typical listening environment (e.g., the classroom, the workplace, the home).
The Assessment Itself
An audiologic evaluation is sometimes thought of as “just a hearing test,” but more than “just” the ability to hear sounds is involved. The audiologic evaluation consists of a battery of tests each providing specific standalone information. Yet, the tests complement one another. The audiologic evaluation consists of several different components.
The audiologist will ask several questions during the case history. For example:
- What brought you here today?
- Have you noticed difficulty with your hearing? What have you noticed? For how long? When do you think the hearing loss began?
- Does your hearing problem affect both ears or just one ear?
- Has your difficulty with hearing been gradual or sudden?
- Do you have ringing (tinnitus) in your ears?
- Do you have a history of ear infection?
- Have you noticed any pain in your ears or any discharge from your ears?
- Do you experience dizziness?
- Is there a family history of hearing loss?
- Do you have greater difficulty hearing women’s, men’s, or children’s voices?
- Do people comment on the volume setting of your television?
- Has someone said that you speak too loudly in conversation?
- Do you frequently have to ask people to repeat?
- Do you hear people speaking, but can’t understand what is being said?
- Do you have any history of exposure to noise in recreational activities, at work, or in the military?
- Are there situations where it is particularly difficult for you to follow conversation? Noisy restaurant? Theater? Car? Large groups?
For children, questions will also be asked regarding:
- speech and language development
- health history
- recognition of and response to familiar sounds
- the startle response to loud, unexpected sounds
- the presence of other disabilities
- any previous hearing screening or testing results
The audiologist will look at the outer ear (the pinna) checking for any malformation. 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.
Tests of Hearing and 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.
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 measurement, another aspect of immittance testing, can add diagnostic information about middle ear function and hearing loss.
After the test battery is completed, the audiologist will review each component of the audiologic evaluation to obtain a profile of hearing abilities and needs. Additional specialized testing may be indicated and recommended on the initial test results. Audiological evaluation may result in recommendations for further follow-up such as medical referral, educational referral, hearing aid/sensory aid assessment, assessment for assistive listening devices, audiologic rehabilitation assessment, speech and language assessment, and/or counseling.
As you can see, an audiologic evaluation is much more than “just a hearing test!”
Pure-tone audiometry is completed in a soundproof booth-a room with special treatment to the walls, ceiling, and floor to ensure that background noise does not affect test results. Only those sounds that the audiologist introduces into the room, either through earphones or through speakers located in the room, will be heard. Sounds may also be sent through a special headset “vibrator” that has been placed just behind the ear or on the forehead.
In testing hearing for tones, a pure tone air conduction hearing test is given to find out the faintest tones a person can hear at selected pitches (frequencies) from low to high. During this test, earphones are worn and the sound travels through the air in the ear canal to stimulate the eardrum and then the auditory nerve. The person taking the test is instructed to give some type of response such as raising a finger or hand, pressing a button, pointing to the ear where the sound was received, or saying “yes” to indicate that the sound was heard.
Sometimes children are given a more play-like activity ( conditioned play audiometry) to indicate response. They may be instructed to string a peg, drop a block in a bucket, or place a ring on a stick in response to hearing the sound. Infants and toddlers are observed for changes in their behavior such as sucking a pacifier, quieting, or searching for the sound and are rewarded for the correct response by getting to watch an animated toy ( visual reinforcement audiometry).
The audiologist uses a calibrated machine called an audiometer to present tones at different frequencies (pitches) and at different intensity (loudness) levels. A signal of a particular frequency (something like a piano note) is presented to one ear, and its intensity is raised and lowered until the person no longer responds consistently. Then another signal of a different frequency is presented to the same ear, and its intensity is varied until there is no consistent response. This procedure is done for at least six frequencies. Then the other ear is tested in the same way.
The frequency or pitch of the sound is referred to in Hertz (Hz). The intensity or loudness of the sound is measured in decibels (dB). The responses are recorded on a chart called an audiogram that provides a graph of intensity levels for each frequency tested.
In some cases, it is necessary to give a pure tone bone conduction hearing test . In this test, the tone is introduced through a small vibrator placed on the temporal bone behind the ear (or on the forehead). This method “bypasses” blockage, such as wax or fluid, in the outer or middle ears and reaches the auditory nerve through vibration of skull bones. This testing can measure functionality of the inner ear independently of the functionality of the outer and middle ears.
Air conduction test results indicate hearing losses that are either conductive or sensorineural. Bone conduction test results reflect only the sensorineural component. By comparing air conduction and bone conduction test results, the audiologist can determine whether there is a hearing loss due to a problem in the outer or middle ear. If air and bone conduction thresholds are the same, the loss is sensorineural. If there is a difference between air and bone thresholds (an air-bone gap), the loss is conductive or mixed.
Speech audiometry includes determining speech reception threshold (SRT) and testing of word recognition . Speech reception threshold testing determines the faintest level at which a person can hear and correctly repeat easy-to-distinguish two-syllable (spondaic) words. Examples of spondaic words are “baseball,” “ice cream,” “hot dog,” “outside,” and “airplane.” Spondaic words have equal stress on each syllable. The individual repeats words (or points to pictures) as the audiologist’s voice gets softer and softer. The faintest level, in decibels, at which 50% of the two-syllable words are correctly identified, is recorded as the Speech Reception Threshold (SRT). A separate SRT is determined for each ear.
Tests of word recognition attempt to evaluate how well a person can distinguish words at a comfortable loudness level. It relates to how clearly one can hear single-syllable (monosyllabic) words when speech is comfortably loud. Examples of words used in this test are “come,” “high,” “knees,” and “chew.” In this test, the audiologist’s voice (or a recording) stays at the same loudness level throughout. The individual being tested repeats words (or points to pictures). The percentage of words correctly repeated is recorded for each ear.
Thus, a score of 100% would indicate that every word was repeated correctly. A score of 0% would suggest no understanding. Word recognition is typically measured in quiet. For specific purposes, word recognition may also be measured in the presence of recorded background noise that can also be delivered through the audiometer.
How to Interpret an Audiogram
The audiogram is a graph showing the results of the pure-tone hearing tests.
Pitch or frequency
Each line from left to right represents a pitch or frequency in Hertz (Hz) starting with the lowest pitches on the left side to the very highest frequencies tested on the right side. The range of frequencies tested by the audiologist are 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz. If you are familiar with a piano keyboard with the low notes at the left end and the high notes at the right end, the audiogram is similar. On the audiogram, 250 Hz is the same as the “middle C” key on the piano.
Examples of sounds in everyday life that would be considered “low frequency” are: bass drum, tuba, and vowel sounds such as “oo” in “who.”
Examples of sounds in everyday life that would be considered “high frequency” are: bird chirping, triangle playing, and consonant sounds such as “s” in “sun.”
If we were to compare a flute playing and a tuba playing, we’d say the flute was primarily high frequency (high pitches) and the tuba was primarily low frequency (low pitches).
If we were to compare the sound of “f” as in “fly” to the sound of “m” as in “moon,” we’d say the “f” was primarily high frequency (high pitch) and the “m” was primarily low frequency (low pitch).
Loudness or intensity
Each line on the audiogram from top to bottom represents loudness or intensity in units of decibels (dB). Lines at the top of the chart (small numbers starting at minus 10 dB and 0 dB) represent soft sounds. Lines at the bottom of the chart represent very loud sounds.
Examples of sounds in everyday life that would be considered “soft” are: clock ticking, whispering, and the consonant sound “t” in the word “too.”
Examples of sounds in everyday life that would be considered “loud” are: lawnmower, car horn, and the vowel sound “o” as in the word “poke.”
If we were to compare the sound of a jackhammer to the sound of a vacuum cleaner, we’d say the jackhammer was “loud” and the vacuum cleaner was “soft.”
If we were to compare the sound of “s” as in “spot” to the sound of “ah” as in “spot”, we’d say the “s” was “soft” in comparison to the vowel “ah.”
If we were to compare “normal conversational loudness level” (typically 60 dB) to “whispering” (typically 30 dB), we’d say that whispering was soft and conversation was loud.
Some audiograms are also divided into sections showing the severity of hearing loss.
As the audiologist tests your hearing, the results are recorded on the graph. At each frequency tested, the “O” represents the softest tone you can hear in your right ear and the “X” represents the softest tone you can hear in your left ear.
If the “X’s” and “O’s” all fall in the -10 dB to 15 dB range, your hearing lies in the normal range. If the “X’s” and “O’s” all fall in the 16 dB to 25 dB range, you have a slight/minimal loss. If the “X’s” and “O’s” all fall in the 31dB to 51dB range, you have a moderate loss. If the “X’s” and “O’s” all fall in the 91 dB and above range, you have a profound loss.
The audiogram configuration may be flat; sloping down, showing better hearing in the low frequencies; or rising, showing better hearing in the high frequencies. The configuration may be symmetrical, showing the same hearing loss for both ears; or asymmetrical, showing a different hearing loss configuration for each ear.
Once the audiogram is completed, the audiologist computes the pure tone average for each ear. It is the average of hearing thresholds at 500, 1000, and 2000 Hz, which are considered to be the major frequencies for speech. The pure-tone average represents the degree of hearing loss in decibels. It is not a percentage.
Right ear=28 dB (mild loss)
Left ear=45 dB (moderate loss)
Other Audiologic Procedures
There are a variety of other audiologic procedures that assess the auditory system and determine the presence of hearing loss. They are sometimes used independently and sometimes used to complement the standard audiologic test battery. They help to supplement information from behavioral testing or to resolve conflicting information from behavioral testing. They are auditory evoked potentials, otoacoustic emissions testing, and acoustic immittance measures.
Auditory Evoked Potentials
Electrodiagnostic test procedures give information about the status of neural pathways. These procedures are used with individuals who are difficult to test by conventional behavioral methods. They are also indicated for a person with signs, symptoms or complaints suggesting a nervous system disease or disorder. Auditory brainstem response (ABR) is an auditory evoked potential that originates from the auditory nerve. It is often used with babies. Electrodes are placed on the head (similar to electrodes placed around the heart when an electrocardiogram is run), and brain wave activity in response to sound is recorded.
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.
Acoustic Immittance Measures
Acoustic immittance measures are a battery of tests including tympanometry, acoustic reflex, and static acoustic impedance.
Tympanometry introduces air pressure into the ear canal making the eardrum move back and forth. The test measures the mobility of the eardrum. Tympanograms or graphs are produced which show stiffness, flaccidity, or normal eardrum movement.
We all have an acoustic reflex to sounds. A tiny muscle in the ear contracts when a loud sound occurs. The loudness level in decibels at which the acoustic reflex occurs, and/or the absence of the acoustic reflex, gives diagnostic information that aids in identifying location of the problem along the auditory pathway.
Through static acoustic measures , the physical volume of air in the ear canal is measured. This test is useful in identifying a perforated eardrum or the openness of ventilation tubes.
Balance Assessment Our sense of balance is determined by our visual system, the inner ear, and our sense of movement via muscles (kinesthetic sense). When these systems don’t work together and function properly, we become dizzy. Dizziness is a symptom. Any disturbance in the inner ear, with or without hearing loss or ringing in the ears (tinnitus), may cause a feeling of dizziness. Dizziness can be caused by disease such as Meniere’s Disease, by small calcium deposits in the inner ear, drugs which are toxic to the vestibular (balance) system, head trauma, and other conditions not necessarily related to the vestibular system. Balance system assessment is conducted to detect pathology with the vestibular or balance system; to determine site of lesion; to monitor changes in balance function; or, to determine the contribution of visual, vestibular, and proprioceptive systems to functional balance. Vestibular or balance system assessment is indicated when a person has nystagmus (rapid involuntary eye movement), complaints of vertigo (dizziness) balance dysfunction, gait abnormalities, or when pathology/disease of the vestibular system is suspected.
Content courtesy: American Speech-Language-Hearing Association (ASHA)