This paperstarted showing the previous literatures compare ABR and ASSR and theadvantages and disadvantage of each one in frequency specificity, effect and modulationfrequency and, automatic detection. With brief description for both of them.
The first study:is a retrospective study to compare c-ABR with ASSRs in estimating audiometricthreshold. Infants and children were tested using visual reinforcementaudiometry or play procedures to estimate behavioral thresholds. ABR thresholdswere determined using click stimuli and threshold was determined at the lowestlevel at which an ABR was present. ASSR thresholds were determined using puretones and threshold was determined as the lowest stimulus level that met thephase-locked response criterion. Results: show that both c-ABR and ASSR have strong andstatistically significant correlations with the pure-tone audiogram in infantsand children with various degrees of hearing loss. The pure tone-ABRcorrelation was higher than ASSR at 1 and 2 kHz and, higher for ASSR at 500 Hzcompared to c-ABR. whereas at 4 kHz, the correlations were identical.
Thediscrepancy between behavioral and evoked potential threshold was generallysmaller for ASSR than for ABR, but the standard deviation of the difference wasessentially the same for both measures. Discussion: unlike previousanalyses of the study, the ABR data were also used, and at 1 and 2 kHz, thepure tone-ABR correlation slightly exceeded those for the ASSR. This wasunexpected because it was thought that ASSRs, evoked by AM + FM tones, wouldyield higher correlations with behavioral thresholds at the same frequencies.However, several factors may contribute to these results including: synchronousdifferences, the instantaneous rise time, frequency specificity, the responsedetection methods used, the “test performance” (sensitivity andspecificity of response judgments) and, nature of pure tone test results. The second study:a prospective study comparing ASSR and tb-ABR using and automatic detectionalgorithm for threshold detection in normal-hearing adults. About visualdetection, seven stimulus levels were recorded and plotted in hardcopy for posthoc judging. The presence or absence of responses is judged by reviewing allresponses.
Threshold was judged to be the lowest stimulus level at which a waveV was visually detected. About automatic detection, calculation of the Fsp andPC2 was used to determine whether a response was present for ASSRtests. Results: Thresholdsfor 500 Hz were elevated relative to those for 4000 Hz, and allthresholds were in accordance with previously published data. There areDifferences in thresholds as a function of test type (visually detected ABR,Fsp detected ABR, ASSR at 41 Hz, and ASSR at 74 Hz) at 500 Hz. Discussion: this study showed that tone-ABR andASSR could both be used to estimate hearing threshold but that the stimulusused (tone burst versus AM + FM tone) and detection method (algorithm versusvisual detection) affected the threshold determination.Strengthsand weaknesses:-In this articleI learned that an audiologist can estimate audiometric thresholds using bothclinical instruments (ASSR and c-ABR). However, there are advantages using ASSRover ABR and vice versa.
–also, I learned that an audiologist can estimatehearing threshold using different stimulus (tb-ABR or FM+AM ASSR) and candetect responses either visually or objectively using algorithms. However different stimulus and detectionmethods will affect the results. Strengths:-Thearticle provides information in a systematic way, enabling the reader to reviewprevious published studies and compare the results easily.-The resultsof the studies are in a good agreement with some published studies and confirmthem.-The present studies investigated and highlighted the limitationsof some previous studies.-Results obtained were explained in details.-The behavioralthresholds included in the first study were all reliable.-This article comparedboth ASSR and ABR thresholds with behavioral thresholds unlike the previousstudies which compare behavioral thresholds with only one electrophysiologicaltest.
Limitations: -Ican notice that the selection criteria (sampling procedure) of the first studyaffect the results.-Gender of participants in first study were not specified. -Inthe first study they didn’t investigate the correlation between behavioralthresholds and electrophysiological thresholds in more profound cases so,further investigations are needed.
-They didn’t mention the reliability of theelectrophysiological thresholds.-ASSR considered as a new clinicalmethod so that audiologists are not familiar with yet. However, this article ispublished in 2002, nowadays most of audiologists are familiar with the ASSR.