TheAuditory Steady-State Response: Comparisons with the Auditory BrainstemResponse Two studies arereported in which the threshold estimates from auditory steady-state response(ASSR) tests are compared to those of click- or toneburst-evoked auditory brainstemresponses (ABRs).Various issuesassociated with the comparison of the two evoked potentials should beconsidered, including frequency specificity, response generators, the effectsof hearing loss and automatic detection algorithms. Two studies wereundertaken that compared the ASSR with the ABR. First, a retrospectivecase review was used to compare ASSR test results in relation to c-ABR. Second,a direct comparison of ASSR and tb-ABR threshold estimation techniques wasconducted using adult listeners. Study 1: comparison ofASSR with ABR results This study reports areanalysis of some data from Rance and colleagues (1995, 1998) to provide someadditional comparisons among audiometric threshold, c-ABR, and ASSRs.
MethodOverall, therewere 192 comparisons between behavioral and evoked potential (ABR and ASSR)thresholds, with 39 at 500 Hz, 78 at 1 kHz, 18 at 2 kHz, and 57 at 4 kHz. ResultsThe results showthat both c-ABR and ASSR have strong and statistically significant (p < .05) correlations with the pure-tone audiogram ininfants and children with various degrees of hearing loss. Thesedata suggest that both c-ABR and ASSR threshold estimates can be used topredict pure-tone threshold for infants and children who have hearingthresholds in the normal to severe-to-profound range.
Study 2: direct comparison of ASSR and toneburs~evoked ABR To address the issue of ASSR versustb-ABR for threshold detection, Kosmider (1997) under took a direct comparisonof ASSR and tone- evoked ABR threshold in normal-hearing adults using the PC2algorithm for ASSR detection and the Fsp algorithm for ABR detection. Method Ten normal-hearingfemale adults, aged 20 to 35 years, participated in the study. Only one ear wastested for each participant; in six cases, this was the left ear. Allparticipants had normal pure tone thresholds established using standardtechniques, with thresholds at or better than 10 dB HL for 250 to 8000 Hz.Tympanometry and acoustic reflex tests were also completed, and the resultswere within the normal range for all participants.
Data AcquisitionParameters ABRswere acquired with the NeuroScan “Scan” system, using a two-channelelectrode montage. For ASSR tests, a single recording montage was used. StimuliFor ABR tests,500- and 4000-Hz tone bursts were used. The ASSR tones were sinusoidallyamplitude modulated with a depth of 100 percent and frequency modulated at 10percent.
ResponseDetection VisualDetection: Thresholdwas judged to be the lowest stimulus level at which an ABR (wave V) wasvisually detected in the waveform. AutomaticDetection: TheFsp was used as the automatic detection method for ABR. Results Thebehavioral thresholds for each of the stimuli used in the experiment aresummarized in the Table Thisstudy showed that tone-ABR and ASSR could both be used to estimate hearingthreshold but that the stimulus used (tone burst versus AM + FM tone) and detection method (algorithm versusvisual detection) affected the threshold determination. DISCUSSIONCalibration and Stimulus Differences Difficulties remain in comparingthreshold estimates for tone ABR and ASSR because ofthe difference in stimuliused. Optimizing Fsp When ABR thresholds were estimated from trialsmeeting the Fsp criterion, the estimated thresholds were significantly higherthan those from visual detection. Electrophysiologictechniques can never truly be “objective” if waveforms need to bejudged subjectively, and techniques such as Fsp offer a means for makingresponse detection and threshold estimation from ABR objective, withidentifiable error rates. Fsp is a robust algorithm and can be improved whenmore is known about the EEG noise characteristics.
ASSR in Adults There,as there is a needto establish ASSR thresholds in normal-hearing listeners with para- metricevaluation of the effects of MF, CF, and subject state, as are only a fewstudies reporting ASSR thresholds in normal-hearing adults.