2. Reference
Cummings Otolaryngology Head & Neck Surgery
FIFTH EDITION
Carolyn J. Brown, Ph.D.
Professor
Department of Communication Sciences and Disorders
Department of Otolaryngology–Head and Neck Surgery
University of Iowa Carver College of Medicine
Iowa City, Iowa
Essential otolaryngology
9th edition
Derald E. Brackmann
MD , FACS
Clinical professor of ORL-HNS
Clinical professor of neurosurgery
University of California school of medicine
President House clinic
Board of Director , House Ear Institute
LA , California
Web site search using the key word “ Auditory steady state response “
3. • Auditory Steady-State Response : is an auditory evoked potential,
elicited with modulated tones that can be used to predict hearing
sensitivity in patients of all ages & to predict hearing thresholds for
normal hearing individuals and those with hearing loss .
• The ASSR uses statistical measures to determine if and when a threshold
is present .
• the ASSR can be successfully recorded even from sleeping children .
• ASSR measures assumed a prominent role either in place of or in
addition to ABR—as a means of estimating audiometric thresholds in
pediatric populations.
• Additionally, the ASSR could be recorded from individuals with no
measurable ABR
4. • It defer from ABR in that the amplitude &/or frequency of the
continuous tone is not constant but modulated at rate between 3-
200 Hz , so the evoked response follow the rate of modulation rather
than the frequency of the tone.
• ASSR that originate in the brain stem can be obtained by using
modulation rate of 70 Hz or greater
• Lower modulation rate can result in ASSR that represent the brain
stem & the cortical area.
5. ASSR vs. ABR
• Both record bioelectric activity from electrodes
arranged in similar recording arrays.
• Both are auditory evoked potentials.
• Both use acoustic stimuli delivered through
inserts (preferably).
• Both can be used to estimate threshold for
patients who cannot or will not participate in
traditional behavioral measures.
Similarities:
6. Differences:
1. ASSR looks at amplitude and phases in the spectral (frequency) domain rather than
at amplitude and latency.
2. ASSR depends on peak detection across a spectrum rather than across a time vs.
amplitude waveform.
3. ASSR is evoked using repeated sound stimuli presented at a high rep rate rather
than an abrupt sound at a relatively low rep rate.
4. ABR typically uses click or tone-burst stimuli in one ear at a time, but ASSR can be
used binaurally while evaluating broad bands or four frequencies (500, 1k, 2k, & 4k)
simultaneously.
5. ABR estimates thresholds basically from 1-4k in typical mild-moderate-severe
hearing losses. ASSR can also estimate thresholds in the same range, but offers
more frequency specific info more quickly and can estimate hearing in the severe-
to-profound hearing loss ranges.
6. ABR depends highly upon a subjective analysis of the amplitude/latency function.
The ASSR uses a statistical analysis of the probability of a response (usually at a 95%
confidence interval).
7. ABR is measured in microvolts (millionths of a volt) and the ASSR is measured in
nanovolts (billionths of a volt).
7. • ASSR can be adversely affected by stimulus
artifact, particularly when stimuli are
presented either at a high level or via a bone
conduction transducer.
• ASSR are very small-amplitude response—
considerably smaller than the ABR. As a result,
obtaining quality ASSR recordings requires
particularly quiet subjects and good control of
physiologic and nonphysiologic noise sources
Disadvantage over ABR
8. Methodology
• The same to traditional recording montages used for ABR recordings.
• Two active electrodes are placed at or near vertex and at ipsilateral earlobe/mastoid
with ground at low forehead.
• If collecting from both ears simultaneously, a two-channel pre-amplifier is used.
• When single channel recording system is used to detect activity from a binaural
presentation, a common reference electrode may be located at the nape of the neck.
• Transducers can be insert earphones, headphones, a bone oscillator, or sound field
and it is preferable if patient is asleep.
• Unlike ABR settings, the high pass filter might be approximately 40 to 90 Hz and low
pass filter might be between 320 and 720 Hz with typical filter slopes of 6 dB per
octave.
• Gain settings of 10,000 are common, artifact reject is left “on”, and it is thought to be
advantageous to have manual “override” to allow the clinician to make decisions
during test and apply course corrections as needed.
• Most equipment provides correction tables for converting ASSR thresholds to
estimated HL
