SERVING STUDENTS WHO ARE HARD OF HEARING
SUMMARY
if one is present, can be determined by reading an
audiogram. The type of hearing loss is determined by
comparing auditory thresholds obtained using head-
phones or insert earphones (air-conduction thresholds)
to those obtained using a bone oscillator (bone-conduc-
tion thresholds). By itself, the audiogram cannot tell us
how an individual will perform in the real world. While
tests of speech perception in quiet and in noise can
greatly enhance the diagnostic value of the audiogram,
the results obtained in a sound booth do not always
translate directly to how an individual will perform in
the real world
KEY TERMINOLOGY
Audiogram
representing the softest sounds that a person can
Decibel (dB)
Decibel refers to the loudness of sounds. A sound
low in dB is perceived as soft and a sound high in dB
is perceived as loud.
dB SPL vs. dB HL
Loudness of sound is typically measured in sound
pressure level (dB SPL). The output of hearing aids
and assistive listening devices is displayed in dB
SPL; however, auditory thresholds (on an audiogram)
are measured in hearing level (dB HL).
Frequency
The unit used to measure frequency is Hertz (Hz).
The perceptual correlate of frequency is pitch. As
frequency increases, so does pitch. Examples of
low frequency (low pitch) sounds include drums and
bass guitars and vowels, while high frequency (high
consonants (f, th, s). Hearing is typically tested
between 250 and 8000 Hz, which is where most
speech sounds fall.
Auditory thresholds
Auditory thresholds are the softest sounds an
individual can detect. They are plotted between -10
and 110 dB HL at octave or mid-octave intervals
from 125 to 8000 Hz. The normal hearing listener
can typically hear sounds as soft as 0 dB HL
and when sounds are above 100 dB HL they are
generally considered to be uncomfortably loud.
KEY CONCEPTS
Conductive hearing losses (CHL)
CHL are characterized by a reduction in hearing ability
despite a normal functioning cochlea (inner ear). This
type of hearing loss is caused by impaired sound
transmission through the ear canal, eardrum, and/
or ossicular chain. Conductive hearing losses are
infections and wax impaction are two common causes
of this type of hearing loss. In conductive hearing
losses, air conduction thresholds are abnormal, bone
conduction thresholds are normal, and an air-bone
gap is present.
Sensorineural hearing losses (SNHL)
SNHL are characterized by a reduction in hearing
ability due to disorders involving the cochlea and/or
the auditory nervous system. This type of hearing loss
is usually irreversible. Sensorineural hearing losses
can be further divided into sensory and neural losses.
A sensory (cochlear) hearing loss occurs when the
damage to the auditory system is located within the
cochlea. Noise induced and age related hearing losses
are typically sensory in nature. A neural (retrocochlear)
hearing loss occurs when the damage to the auditory
system is beyond the level of the cochlea, ranging
anywhere from the hearing nerve up to the brain. A
tumor on the hearing nerve can be one cause of a
neural hearing loss. In sensorineural hearing losses, air
conduction and bone conduction thresholds are both
abnormal, but are impaired to approximately the same
degree (no air-bone gap present).
Mixed hearing losses
Mixed hearing losses occur when both conductive and
sensorineural components are present. As in conduc-
tive hearing losses, the conductive component of a
In mixed hearing losses, air conduction and bone
UNDERSTANDING AN AUDIOGRAM
Marni L. Johnson
University of South Dakota
