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1- The
ASSR overcomes some of the limitations of ABR testing which include that the
steady-state response is evoked by pure tones that are amplitude and/or
frequency modulated unlike ABR which lack frequency specificity.

2-One of
the advantages of using ASSRs to determine residual hearing thresholds for
infants and children from whom ABRs could not be evoked. Also it determine
residual hearing thresholds for those infants and children from whom ABRs could
not be evoked.

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3- When
we compare ASSR to behavioral threshold the findings will be are very similar
both qualitatively and quantitatively.

5- A
disadvantage of ABR regarding audiologic applications is the subjective nature
of response detection while ASSR use objective detection using a set of
statistical criterion previously obtained.

 

STUDY 1: COMPARISON OF ASSR WITH
ABR RESULTS:

ABR may
be better because the technology is more widely available and many of the
stimulus and pathologic variables have been defined. However, in some cases,
ASSRs were present when ABRs were not, suggesting an advantage for ASSR. In
order to obtain the results, Behavioral Threshold Tests, ABR Threshold Tests
and ASSR Threshold Tests Were conducted.

 

Results:

1-The
results show that both click-ABR and ASSR have strong significant correlations.

2-The
discrepancy between behavioral and evoked potential threshold was generally
smaller for ASSR than for ABR.

3-Positive
values indicate that the evoked potential thresholds were found at levels greater
than for behavioral thresholds, and negative values mean that the evoked
potential thresholds were at levels less than behavioral thresholds. 

4-The correlation of ABR with pure- tone threshold was
marginally higher than for ASSR at 1 and 2 kHz, whereas at 4 kHz, the
correlations were identical.   

5-The correlations of c-ABR with pure-tone thresholds were
moderately robust. At 1 and 2 kHz, the pure tone-ABR correlation coefficients
slightly exceeded those for the ASSR.   

 

Discussion:

1-Unexpectedly
at 1 and 2 kHz, the pure tone-ABR correlation coefficients slightly exceeded
those for the ASSR.

2-The
differences between the ABR and ASSR correlation coefficients were small. The
correlations between the c-ABR threshold and the ASSR thresholds were
statistically significant.

3- These data suggest that both c-ABR and ASSR threshold estimates
can be used to predict pure tone threshold for infants and children who have
hearing thresholds in the normal to severe-to-profound range.   

5-Regarding
the ASSR, threshold was defined as the lowest level at which a statistically significant
(p < .01) Phase coherence result was obtained. For ABR, threshold was defined as the lowest level for which a time-domain waveform was visually detected by an observer.   STUDY2: DIRECT COMPARISON OF ASSR AND TONE BURS~EVOKED ABR: ASSR tests were carried out using 500- and 4000-Hz. ABRs were acquired with the Neuro Scan "Scan" system, using a two-channel electrode montage. Response Detection include: Visual Detection and Automatic Detection.   Results: 1-Thresholds for 500 Hz were elevated relative to those for 4000 Hz.   Discussion: 1-Visual detection of the 500Hz tone burst 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. 2-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: 1-      In regards to study 1 unlike previous analyses that addressed only ASSR-behavioral threshold correlations, the ABR data were also used.   2-      In regards to study 2 previous studies comparing ASSR to tb-ABR have employed visual detection alone for ABR threshold estimates and have only compared tone ABR to ASSR at one frequency. however, this study includes findings at more than one frequency. 3-      In regards to study 2 all participants had normal pure tone thresholds.   Weaknesses: 1-      ASSR is that its not approved by Food and Drug Administration (FDA). 2-      In regards to study 1it has been established that thresholds in dB SPL, when measured in the ear canal, are substantially different in infants compared to adults. 3-      In regards to study 1 more than half of the sample are SNHL in comparison to CHL and normal subjects. 4-      In regards to study 1the 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. 5-      In regards to study 2 most of the participants slept during testing ASSR and the thresholds were lower. 6-      In regards to study 2 only one ear was tested for each participant in both ABR and ASSR. No formal assessment was made of subject status during the experimental procedures.

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