The 1000 and 2000 Hz. Also, there was a

Auditory Steady-State Response: Comparisons with the Auditory Brainstem

        This article presented two studies
which compared the thresholds obtained from auditory steady-state response
(ASSR) tests and those obtained from click or tone burst evoked auditory
brainstem responses (ABRs).

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      The first study presented a comparison
between ASSR and ABR results. 51 Cases were included. Participants who exhibited
profound hearing loss and an interval of more than 24 months between ABR, ASSR,
and behavioral threshold tests were excluded. The participants ranged from mild
hearing to severe-to-profound hearing losses. Also, Subjects had different
types of hearing losses. Comparisons
were done between behavioral and evoked potential (ABR and ASSR) thresholds at
500, 1000, 2000 and 4000Hz. In behavioral threshold tests, 500, 1000 and 4000
Hz were used to establish thresholds. In ABR threshold tests, thresholds were
determined using 100 f.Lsecclick . In ASSR threshold tests, thresholds were
determined using pure tones at 500, 1000, 2000, and 4000 Hz that were amplitude
and frequency modulated at 90 Hz. Results show that both c-ABR and ASSR have
strong correlations with the pure-tone audiogram in infants and children with
various degrees of hearing loss. The correlation of ABR with pure tone
threshold was higher than ASSR at 1000 and 2000 Hz. Also, there was a higher
correlation between ASSR and behavioral thresholds at 500 Hz compared to the
c-ABR. Several factors contributed to these results. First, clicks evoke a more
synchronous neural response than modulated tones. In contrast, the rise times
of a modulated tone are prolonged relative to the click.  Also, threshold for ASSR was defined as the
lowest level at which a statistically significant (p < .01) PC result was obtained. For ABR, threshold was defined as the lowest level based on a time-domain waveform that was visually detected and the observer was not blinded to the subjects' audiometric results, so observer bias might have affected the response judgments. The high correlation of c-ABR with the pure tone audiogram also depends on the nature of pure tone test results. In this sample, most audiograms had flat or only mildly sloping configurations because participants with profound losses have been eliminated. As a result, the individual pure-tone thresholds would be highly correlated. So, ABR and pure-tone threshold correlations were high because only one ABR threshold was compared with four pure-tone thresholds. For the ASSR, four separate correlations have been made, one for each ASSR test frequency and pure-tone threshold.  This data suggest that both c-ABR and ASSR threshold estimates can be used to predict pure-tone threshold for infants and children.         In the second study, a direct comparison of ASSR and tone evoked ABR was done. The PC2 algorithm was used for ASSR detection and the Fsp algorithm for ABR detection. Participants were ten normal hearing female adults and test was performed unilaterally. All participants had normal pure-tone thresholds. For ABR tests, 500 Hz and 4000 Hz tone bursts were used. ASSR tests were carried out using 41 Hz and 74 Hz MFs for 500 Hz and 41 Hz and 95 Hz MFs for 4000 Hz. For ABR and ASSR tests, stimuli were presented at 50, 30, 20, 15, 10, 5, and 0 dB SL. For response detection, two approaches were used which are the visual detection approach and the automatic detection approach. For 500 Hz, the ASSR at 41 Hz and tb-ABR detected by Fsp resulted in the same threshold. Visual detection of the 500-Hz tb-ABR resulted in a significantly lower threshold compared to other measures at 500 Hz. The 500 Hz ASSR at 74 Hz resulted in the highest threshold. The visual detection of tb-ABR at 4 kHz also resulted in the lowest threshold, but this was not significantly different from the threshold obtained for ASSR at 95 Hz. The thresholds obtained from 4-kHz ASSR at 41 Hz and for 4-kHz ABR-Fsp didn't defer significantly. Over all, results demonstrated that the tone burst-evoked ABR and the modulated tone-evoked ASSR thresholds were similar when both were detected with an automatic detection approach and that thresholds varied with frequency, stimulus rate, and detection method.       To conclude, the strength of the first study was that participants with a variety of hearing loss types were included in the study which maximizes the usefulness of the results. Yet, the weaknesses were that first, participants with profound hearing loss were excluded from the study. Second, the observer reviewed the participants' audiometric status which may lead to tester bias. On the other hand, the strength of the second study was that higher MFs in ASSRs tests were included because they are generated at the brainstem level, making them comparable to tb-ABR tests. Whilst, the weaknesses were that all participants were females and the tests were performed unilaterally (left ear).