Transcript Pure Tone Audiometry

Pure Tone Audiometry
• most commonly used test for evaluating
auditory sensitivity
• delivered primarily through air conduction
and bone conduction
• displayed on a graphic plot called an
audiogram
• audiogram represents a patient's ability to
hear sounds compared with the hearing
sensitivity of a group of normal young adults
Pure-Tone Air-Conduction Testing
• measure the function of the total hearing system,
including the external, middle, and inner ear
• Hughson-Westlake "ascending method" - sounds
are initially presented well above threshold,
decreased to a level of inaudibility in 10- to 15-dB
steps, and then increased in "up 5-dB, down 10dB steps" until the single hearing level at which a
response is obtained three times is reached.
• Because air-conduction thresholds measure the
acuity of the entire hearing system, when
evaluated alone they provide little information
regarding the etiology of hearing loss and specific
auditory pathology.
• When examined in conjunction with thresholds
obtained by bone-conduction testing, however,
they help determine both the type and severity
of the hearing loss.
• 0- to 25-dB – normal
• >25 dB - various levels of hearing loss
Pure-Tone Bone-Conduction Testing
• provide auditory threshold information when the
cochlea is stimulated more or less directly, with
stimuli bypassing external and middle-ear
structures
• differences between thresholds obtained through
air and bone conduction are used to determine
the type of hearing loss (normal hearing vs
conductive loss vs sensorineural hearing loss
[SNHL]) and the magnitude of conductive hearing
loss if it exists
• conductive - when air-conduction thresholds
are elevated relative to normal boneconduction thresholds (air-bone gap)
• sensorineural - when air-conduction and
bone-conduction thresholds indicate the same
amount of hearing loss
• mixed - when air-conduction thresholds are
elevated relative to abnormal boneconduction thresholds
Speech Testing
• evaluation of the listener's ability to detect
and recognize speech
• determination of the speech detection
threshold (SDT), speech reception threshold
(SRT), and speech discrimination or
recognition
• SDT - indicative of the intensity level at which
a listener can barely discern the presence of a
speech signal 50% of the time
• listener is not required to recognize the
stimulus but is merely asked to acknowledge
its presence
• SRT requires the listener to repeat the word
that was presented.
• The SRT is usually 8 to 9 dB higher than the
SDT, whereas the SDT usually coincides with
the pure-tone average (PTA; an average of the
pure-tone thresholds obtained at 500, 1000,
and 2000 Hz).
• Speech discrimination provides information
regarding the listener's ability to recognize
speech under well-controlled conditions.
• monosyllabic words presented in an open-set
format, such as the CID W-22 word lists and NU-6
• Taped materials are optimal but materials are
often presented through live voice for rapidity
and ease of administration
• Speech discrimination materials are usually
presented 50 dB above the patient's SRT which
should be well within their audible range.
Masking
• When conducting either pure-tone or speech
testing, a masking signal to the ear that is not
being tested may be needed. If a sufficiently
loud signal is presented to the test ear, it may
cross the skull where it will be perceived by
the non-test ear, a phenomenon referred to as
crossover.
• When this occurs, responses to air-conducted
pure tones that have crossed over from the
poorer ear will actually shadow the thresholds
of the better ear. Such "shadow" responses
reflect the threshold levels of the better ear,
elevated by the amount of interaural
attenuation at each test frequency.
• interaural attenuation - reduction in sound
when it crosses from one ear to the other