Terminology and Symbols
goal of audiometric testing is to produce an audiogram. The audiogram
charts hearing ability, specifically, the softest sounds that can be heard
in ears at various low-to-high frequencies. These sounds are called
Technically, a person's hearing threshold is defined as "the softest
sounds a person hears at each frequency approximately 50% of the time."
Keep in mind that an audiogram is a quantitative measure, not a
measure of quality (i.e. clarity of speech and other sounds).
An audiogram is a graph, with frequency, from low to high, across
the top or horizontal axis and intensity, from soft to loud, down
the vertical axis.
|Intensity is measured in decibels (dB HL).
The top line, at 0 decibels (dB HL), represents a very soft sound, with
each horizontal line below representing successively louder sounds.
Zero (0) dB HL does not mean that there is no sound at all. Rather,
it is the softest sound that a person with "normal" hearing ability would
be able to detect at least 50% of the time. (Some audiograms, in fact,
begin at -10 dB HL or lower.)
Audiologists consider 0 -15 dB HL to be "normal hearing" in children
(0 - 25 dB HL in adults).
Frequency is measured in
(Hz). Just like a piano's
keyboard, the frequencies are low on the left side (125 or 250Hz), and
then gradually climb to higher frequencies on the right side (8000Hz).
The piano ranges actually go from 28 Hz to 4,000 Hz.
The most important frequencies for speech fall into the 250-6000 Hz
range. The vowel sounds of speech are typically low frequency sounds
that make up the loudness of speech. The consonant sounds like "f",
"s", and "th" are high frequency sounds.
In testing, an audiometer delivers "pure tones" at different frequencies
(Hz) from low to high at different intensities (dB). Air conduction
testing uses earphones or loudspeakers (in a sound-proof room/soundfield).
These send sounds to the ear canal and through the middle ear to reach
the inner ear. Hence air conduction evaluates the whole ear system -- outer,
middle, and inner ear. In bone conduction testing (shown at right),
a bone vibrator is placed behind the ear to deliver the sound vibrations
to the cochlea (the hearing organ of the inner ear). This allows the examiner
to bypass the entire outside and middle ear areas and test the sensitivity
of the inner ear directly.
In "conventional" audiometry, the child (5+ yrs.) presses a button or
raises a hand each time he or she hears a sound. For younger children,
examiners introduce reward (e.g. visual reinforcement audiometry (VRA):
7-30 mos.) and/or play (e.g. conditioned play audiometry (CPA): 30 mos.
- 5 yrs.) "incentives" into testing. As the child responds to the presented
tones and thresholds are determined and marked across the audiogram, the
graph fills in to present a picture of the child's hearing ability.
||In the audiogram to the left, the white area represents
the sounds that the child cannot hear (softer than his/her thresholds)
and the yellow area indicates all of the sounds that the child can
hear (louder than his/her thresholds). Recall that audiologists consider
0-15 dB HL to be normal in children. It is obvious that this child has
a hearing problem!
||There are different styles of audiograms, but most use
a standard set of symbols for representing items on the chart.
review the key that accompanies each audiogram to verify that it uses symbols
you are familiar with.
The terms and symbols below may be used on the audiogram to describe
information about hearing.
Sheet for Reading an Audiogram. A handy reference, designed to be given
to parents/caregivers, to make audiogram information less complicated to
||The measurement standard for the frequency or
frequency of sound. On an audiogram, these typically range from 250 Hz
to 8000 Hz.
||The measurement standard for the amplitude or
loudness/intensity of sound. On an audiogram, these typically range from
0 to 110 dB HL.
||When both ears are tested, thresholds for the left ear
typically appear in blue and for the
right ear, in red.
||In air conduction testing, the symbol 0
stands for the right ear and is usually recorded in red.
X, typically marked in blue,
represents the left ear.
||When a bone-conduction vibrator is used to test
for thresholds, a > symbol is used
for the left ear and a < symbol
is used for the right ear. (Sometimes there will be no color or shapes.
So, remember: check the key/code.) An easy way to remember which symbols
are right vs. left is to imagine the child is facing you. <O>Their
right ear will be on your left, so you use the symbol <
and vice versa.
||These symbols indicate there was no response to the given
|Masking symbols: The term masking refers
to noise presented to the non-test ear to keep it busy," preventing it
from hearing the sound presented to the test ear. The sound is a noise,
which sounds like static, but has tonality. By properly presenting masking
noise to the non-test ear, you can ensure that you are testing the ear
to which the pure tone is presented.
| Pure Tone
|The average of the three thresholds at 500 Hz, 1000 Hz.
and 2000 Hz. For example, when a hearing loss is described as 70 dB HL,
that number probably represents the PTA.
||Symbol for aided audiogram, representing the hearing
level with amplification with hearing aids (A) or cochlear implants (C
or CI). While some audiologists may still conduct functional-gain measurements,
recent technological advances, i.e. Real-Ear Measurements (REM) have made
|For bilateral cochlear implants, Left
or Right, you may see these symbols.
Hearing Loss: A Matter of Degrees
Recall that 0 dB HL is the softest sound that a person with "normal" hearing
ability would be able to detect at least 50% of the time. What exactly
is "normal?" Hearing loss ranges, defined in dB HLs, have been established
to help people identify how much difficulty they should expect from a hearing
loss. The ranges that are listed below -- normal, mild, moderate, severe,
and profound -- are fairly standard across the United States, although
some variations do exist.
Degree of hearing loss based on PTA:
to hear the effect of the hearing loss.
||015 dB HL (infant)
0-25 dB HL (adult)
||20-40 dB HL
Unable to hear soft sounds. Can hear a normal conversation in a quiet
room but has difficulty in a noisy environment. Cannot hear whispered conversation
or speech from a distance.
||40-70 dB HL
Has difficulty hearing a normal conversation in a quiet room. Must
lip-read or use amplification to understand most words.
||70-90 dB HL
Cannot hear a conversation unless the speaker speaks loudly near the
||90+ dB HL
Cannot understand speech even if the speaker shouts. Can only hear
very loud sounds such as a motorcycle engine, if at all.
more detail, see Hearing
Let's look at 4 sample audiograms illustrating air conduction testing:
This shows a mild hearing
loss in both ears in the high frequencies. On average, however, hearing
Masked air thresholds: Note
that in the lower frequencies, the hearing sensitivity is normal in both
ears, but falls sharply into the moderate hearing loss range beginning
at 2000 Hz.
Here we see striking differences
between the ears. The left ear shows normal hearing in the low frequencies
sloping to a severe high frequency hearing loss. The right ear shows a
moderate to severe hearing loss.
This shows a bilateral mild
sloping to profound hearing loss.
||Although these audiograms help us to identify the degree
of hearing loss with pure tones, they do not indicate the type of hearing
loss (because bone-conduction testing is not included) and provide little
detail on the person's ability to understand speech. Mapping conversational
speech on an audiogram (the "speech banana"), then superimposing the audiograms
over these sounds, gives us more more information to interpret the results.
When we look at the speech banana, we see that:
Consonants play big role in our ability to understand speech. For example,
they indicate possession or whether a word is plural and help us to distinguish
one word from another (hot versus hop). How
does this apply to our sample audiograms?
vowels fall in the "louder" ranges (They lie lower on the chart.);
consonants are higher-pitched than vowels (They lie more to the right on
the chart.); and
consonants are spoken more softly than vowel. (They lie higher on the chart,
in the lower decibel ranges.)
Bilateral normal sloping
to mild hearing loss. Under perfect listening conditions, this child will
miss a few words off and on because of not hearing "s" and "th," for example.
Under noisy conditions, he/she will have even more difficulty.
Bilateral normal sloping
to moderate hearing loss. Both ears hear the vowels and the lower-frequency
consonants, but miss "s", "th" and "t," among others. This child would
not be able to distinguish plural from singular forms.
Normal sloping to profound
hearing loss in the left ear. Moderate to severe hearing loss in the right
ear. This child can hear no conversation in the right ear. The left ear,
however, hears all but the soft, upper frequency consonants.
Bilateral mild sloping to
profound hearing loss. With only a few consonant and vowels sounds audible,
this child would miss most of the distinguishing speech features.
Type of Hearing Loss
So far we have examined audiogram results with air conduction testing.
Recall that the air conduction test evaluates the entire hearing mechanism
-- the outer, middle, and inner ear -- and helps pinpoint whether a hearing
loss exists in one ear or both ears at frequencies that are critical to
normal speech and language development.
If a hearing loss exists, bone conduction helps us to determine whether
the problem is in the outer, middle, or inner ear. Recall that the bone
conduction test zeroes in on the inner ear, bypassing the middle and outer
ear. If the air conduction thresholds show a hearing loss but the bone
conduction thresholds are normal, the hearing loss is conductive --
there is a problem involving the conduction of sound through the outer
or middle ear. If both the air conduction thresholds and the bone
conduction thresholds show the same amount of hearing loss, this indicates
the problem is in the inner ear alone, since the results are the same regardless
of whether the outer and middle ears are being tested -- the hearing loss
is sensorineural. And finally, a mixed hearing loss is when
the bone conducted thresholds show a hearing loss and the air conducted
thresholds show an even greater hearing loss. In this case, the problem
lies in the inner
ear (the sensorineural component) and the outer and/or middle
ear as well (the conductive component), hence mixed.
Summarizing the test implications:
||When air conduction tests show a hearing loss, but there
is no loss identified with bone conduction tests, there may be a conductive
||When both air and bone conduction results show hearing
loss at the
same level, the loss is considered
||If different degrees of hearing loss are found via air
and bone conduction testing, the loss is mixed.
||With this in mind, let's look at some sample audiograms
showing bone-conduction testing:
Normal sloping to moderate
hearing loss in the left ear.
Moderate mixed hearing
loss for the left ear.
hearing loss in the left ear. Normal sloping to moderate sensorineural
hearing loss in the right ear.
Mild to moderate conductive
hearing loss in the right ear
||To summarize, by comparing air conduction with bone conduction
thresholds at each frequency, we can determine 1) how well a child hears
at low, medium and high frequencies and 2) if a hearing loss is present,
whether it is
conductive (potentially medically treatable) or sensorineural
(usually permanent and not medically treatable) or mixed.
A final note: The ability to process and interpret sound, as
well as the ability to speak, depends on the interaction of numerous factors
in each individual's background. Two people with similar audiograms may
function very differently!
There are excellent interactive tutorials available at AuDStudent.com's
"Tutorial on Understanding Audiograms," specifically:
Types of Loss on Audiograms
FIRST YEARS wishes to thank Cathy Constantine, audiology doctoral
student in the UNC-CH Division
of Speech and Hearing Sciences, for her assistance in developing this
Many of the audiogram examples, although modified for use here, were taken
from originals from two sources: the Hearing
Alliance of America and Raising
Deaf Kids, both by permission.
Photograph depicting bone conduction testing from My
Baby's Hearing (by permission).