Recent studiesillustrated that auditory steady-state response (ASSR) and auditorybrainstem responses (ABR) can be used to estimate pure-tone threshold ininfants and children at risk for hearing loss in addition to normal-hearingadults. ABR as a clinical tool can be used to estimate threshold, for newbornhearing screening, or for determining whether a hearing loss may be sensory,neural, or retro-cochlear.
The ASSR overcomes some of thelimitations of ABR testing because, the ASSR is evoked by pure tones thatare amplitude and/or frequency modulated. The followingare two studies that compared the threshold estimates from auditorysteady-state response (ASSR) tests with the thresholds of click and toneburst-evoked auditory brainstem responses (ABR): Study 1: Comparisonof ASSR With ABR Results:Retrospective case review was used to compare ASSR test results inrelation to click-ABR (c-ABR). BehavioralThreshold Tests, ABR Threshold Tests and ASSR Threshold Tests were conducted inorder to obtain the results. Results: Correlations were determinedbetween ABR threshold (in nHL) with each audiometricthreshold (in dB HL) and between ASSRthresholds and audiometric thresholds (both in dB HL). The results showed that both c-ABR and ASSR have strong andstatistically significant correlations. The discrepancy between behavioral and evoked potentialthreshold was generally smaller for ASSR than for ABR Discussion: The obtained data suggested thatboth c-ABR and ASSR threshold estimates may be useful to predict pure-tonethreshold for infants and children who have hearing thresholds in the normal tosevere-to-profound range. For the ASSR, threshold was defined as the lowestlevel at which a statistically significant result was obtained.
ForABR, threshold was defined as the lowest level for which a time-domain waveformwas visually detected by an observer. The differences between the ABR and ASSRcorrelation coefficients were small. Strengths: The ABR datawere used in contrast to the previous analyses that addressedonly ASSR-behavioral threshold correlations.
Weakness: · They used adult’s calibration values toreport behavioral and ASSR thresholds andit has been established that thresholds are substantially different in infantscompared to adults. · 31participants (greater than the half of the sample) had sensorineuralhearing loss, so the sample distribution was not equal. · The observer’s sensitivity and specificity of responsejudgment for the visual observations was undefined. Study 2: DirectComparison of ASSR and tone burst evoked ABR: ASSR testswere carried out using 500 and 4000 Hz.
ABRs wereacquired with the Neuro Scan “Scan” system, by using a two-channelelectrode montage. The response detection included visual detectionand automatic detection. Tone burst ABR (tb-ABR) and ASSR wereused to estimate hearing threshold. However, the stimulus used (tone burstversus amplitude modulated + frequency modulated tone) and detection methodused (algorithm versus visual detection) can affect the thresholddetermination. Result: Thresholdsfor 500 Hz were elevated relative to those for 4000 Hz. In addition, thresholdsfor tone bursts were elevated. Discussion: Visualdetection of the 500 Hz tb-ABRresulted in significantly lower threshold estimates compared to other measuresat 500 Hz, and the 500 Hz ASSR at 74 Hz resulted in the highest thresholdestimates. Visualdetection of tb-ABR at 4kHz also resulted in the lowest threshold estimate, but this was notsignificantly different from the estimate obtained for ASSR at 95 Hz.
Strengths: · This study includes findings at morethan one frequency, in contrast to the previous studies which have only comparedtone ABR to ASSR at one frequency.· All participants had normalpure-tone thresholds. Weaknesses: · Most of theparticipants slept during testing ASSR which affected their thresholds (lowerthresholds). · They tested one ear only for eachparticipant in both ABR and ASSR.
· No formal assessment was made ofsubject status during the experimental procedures. · There some difficulties remain incomparing threshold estimates for tone burst ABR and ASSR because of thedifference in stimuli used.