brain stem response is used clinically to estimate threshold for newborn
hearing screening or determining whether a hearing loss may be sensory, neural
or retro-cochlear. The ASSR overcomes some of the limitations of ABR
testing because, the ASSR is evoked by pure tones that are
amplitude and/or frequency modulated. 


The following
are two studies that compared the threshold estimates from auditory
steady-state response (ASSR) tests with the thresholds of click and tone
burst-evoked auditory brainstem responses (ABR):

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Study 1:
Comparison of ASSR With ABR Results:

Compared ASSR test results in
relation to click-ABR (c-ABR). Behavioral Threshold Tests, ABR Threshold
Tests and ASSR Threshold Tests were conducted in order to obtain the results. 


were determined between ABR threshold (in nHL) with each audiometric threshold (in dB HL) and between ASSR thresholds and audiometric thresholds (both in dB HL). The
results revealed that both c-ABR and ASSR have highly and statistically
significant correlations.
Smaller threshold for
ASSR than ABR was the discrepancy between behavioral and evoked potential


 C-ABR and ASSR threshold estimates may be
useful to predict pure-tone threshold for infants and children who have hearing
thresholds in normal to severe-to-profound range as data suggested.  In ASSR, it defines threshold as the lowest
level at which a statistically significant result was obtained. In ABR, it
defines threshold as the lowest level for which a time-domain waveform was
visually detected by an observer. small differences were noted between ABR and
ASSR correlation.



This study considered the instrument
output limits and excluded data with profound hearing loss.

Data with period between the ABR,
ASSR and behavioral threshold tests was more than two months were excluded from
the study.

ASSR results are obtained using PC
which avoids bias judgments.



Clicks evoke more synchronous neural
response than modulated tones, which is a factor that could contribute to the
study results.

Case selection criteria excluded
profound losses at any frequency.

calibration values were used to report thresholds and it has been revealed that
thresholds are different in infants compared to adults.

ABR results are obtained by an
observer which may result in bias judgments.


Study 2:
Direct Comparison of ASSR and tone burst evoked ABR: 

ASSR tests used 500 and 4000Hz, and responses
were detected automatically using algorithms. ABR used two-channel electrode
montage and neuro scan system to obtain results, and responses were detected
visually by the subject. To estimate threshold, Tone burst ABR (tb-ABR) and
ASSR were used. Nonetheless, ABR used tone burst stimulus while ASSR used
amplitude modulated + frequency modulated tone.


Elevated thresholds for 500Hz relatively to
those for 4000Hz. Additionally, tone burst thresholds were elevated.



500Hz tb-ABR visual detection resulted in lower
threshold estimated in comparison to other measures at 500Hz and at 4000Hz it
also resulted in the lowest threshold estimates. and the 500Hz ASSR at 74Hz it
resulted with high threshold estimates and at 4000Hz it was not significantly
different at 95Hz than the one obtained in tb-ABR.


In contrast to the 1st study which
compared tb-ABR to ASSR at one frequency, this study used more than one
frequency in comparison.

Ø   All
participants had normal pure-tone thresholds.

Both tests ABR and ASSR were carried
in the same settings, room that is sound-treated, custom-built with lights off.



Ø  During ASSR
testing, most of the participants slept, which affects their thresholds (lower
thresholds obtained)

For each participant, only one ear was tested
in both ABR and ASSR.

No formal assessment was made of subject
status during the experimental procedures. 


Ø  Normal hearing subjects, while tests are
usually used to estimate threshold in infants, children and adults with hearing

Ø  Stimulus type was different in both tests,
ABR used frequency specific while ASSR used AM and FM, which causes
difficulties in comparing threshold estimates

Ø  Normal ASSR thresholds range reported in the
study varied across researchers.

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