Two studies reported
that auditory steady-state response (ASSR) and
auditory brainstem responses (ABR) can be used to estimate pure-tone threshold
in infants and children at risk for hearing loss in addition to normal-hearing
adults. ABR can be used to 1.estimate threshold, for 2.newborn hearing
screening, or for 3.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. 

Mentioned
below are the studies that illustraited the comparison between the threshold
estimates from (ASSR) tests with the thresholds of click and tone burst-evoked
(ABR):

 

1st
Study: Comparison of ASSR With c-ABR Results:

Reanalysis of some data in the case review was done to
compare 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. 

 

Results: 

Pearson product-moment correlations 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 showed that both c-ABR and ASSR have strong statistically correlationsat and
at levels greater than behavioral thresholds with various degrees of hearing
loss. The discrepancy between behavioral and evoked
potential threshold was generally smaller for ASSR than for ABR.
Click-evoked ABR thresholds and ASSR thresholds may be used together.

Discussion: 

Findings suggested that both c-ABR and ASSR
threshold estimates may be useful to predict pure-tone threshold for infants
and children with different hearing level degrees. For the ASSR, threshold was
defined as the lowest level at which a statistically significant
result was obtained. For ABR, threshold was defined as the lowest level for
which a time-domain waveform was visually detected by an observer. The
differences between the ABR and ASSR correlation coefficients were small.  

   

Strengths:  

·        
The ABR data
were used in contrast to the previous analyses that addressed
only ASSR-behavioral threshold correlations.   

·        
Infants and children were tested
while asleep for ABR and a larage sample=2000 were obtained at each test level.

Weaknesses:  

·        
31 participants out of 51 had sensorineural
hearing loss, so sample distribution was not equal.  

·        
The observer was not blinded with
respect to the subjects’ audiometric status, and so it is possible that some
observer bias may have crept into the response judgments.

·        
only one ABR threshold was compared
with up to four pure-tone thresholds. For the ASSR, there could be as many as
four separate correlations, one for each ASSR test frequency and pure-tone
threshold. Also, behavioral measures and evoked potential measures were
separated in time by weeks, sometimes months.

·        
clicks evoke a more synchronous neural
response than modulated tones. Also, evokes a wide pattern of excitation along
the basilar membrane. In addition the instantaneous rise time of a click will
evoke a synchronous firing from those neurons with the shortest group latency
delays in the basal end of the cochlea. And the rise times of the individual
modulation envelopes in a modulated tone are prolonged relative to the click. Although
the tonal stimulus has better frequency specificity, some synchrony is
sacrificed.

·        
The observer was not blinded with
respect to the subjects’ audiometric status, and so it is possible that some
observer bias may have crept into the response judgments.

·        
Most of behavioral threshold are
minimum response levels based on VRA, above true threshold.

·        
They used adult’s calibration values to report behavioral and ASSR
thresholds.

 

2nd Study: Direct Comparison of ASSR and Tone burst ABR:

Comparison
done for normal-hearing adults using the PC2 algorithm
for ASSR detection and the Fsp algorithm for ABR detection. The response detection
included visual detection and automatic detection.  tb-ABR and
ASSR were used to estimate hearing threshold. However, the stimulus used (tone
burst versus amplitude modulated + frequency modulated tone) and detection
method used (algorithm versus visual detection) can affect the threshold
determination.    

  

Result: 

Thresholds for tone bursts were elevated with
respect to those for tones, owing to temporal summation. Also, thresholds for
500 Hz were elevated relative to those for 4000 Hz.

Discussion: 

This study showed that tone-ABR and ASSR could both
be used to estimate hearing threshold but that the stimulus used and detection
method affected the threshold determination. Visual detection of the 500 Hz tb-ABR resulted in significantly lower threshold estimates
compared to other measures at 500 Hz, and the 500 Hz ASSR at 74 Hz resulted in
the highest threshold estimates. Visual detection of tb-ABR at 4 kHz also resulted in the lowest threshold
estimate, but this was not significantly different from the estimate obtained
for ASSR at 95 Hz. 

  

Strengths: 

·        
This study includes findings at more than one
frequency, in contrast to the previous studies which have only compared tone
ABR to ASSR at one frequency.

·        
 All
participants had normal pure-tone thresholds.

·        
The ASSR and tb-ABR tests were
carried out in a darkened, custom-built, sound-treated room.

·        
Improved SNR of the recording due to
more sweeps (up to 6000) were averaged at nearthreshold levels.

·        
Automatic detection
algorithm for ASSR and ABR ensured an objectively interpreted responses.

Weaknesses: 

·        
Most of the
participants slept during testing ASSR which affected their thresholds (lower
thresholds).

·        
They tested one ear only for each participant
in both ABR and ASSR. 

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

·        
Difficulties
in comparing threshold estimates for tone burst ABR and ASSR due to difference
stimuli used. 

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