| Objective auditory evoked potentials (AEPs) are more commonly being used to predict or estimate pure-tone thresholds, in particular when testing difficult to test populations, such as infants and children. A new class of AEPs, referred to as auditory steady-state responses (ASSR), has recently emerged as a clinical technique in audiology. An objective physiologic test that can reliably estimate air-bone gaps or the degree of conductive hearing loss, particularly in infants and children is of clinical value. The primary purpose of this study was to investigate whether ASSR is a reliable and accurate testing tool for estimating hearing thresholds when a conductive hearing loss is present. In addition, the sensorineural acuity level (SAL) technique, an alternate approach to traditional bone-conduction testing, was applied to both behavioral testing and ASSR testing to estimate BC thresholds and the air-bone gaps produced by the simulated conductive hearing loss. The application of this procedure with measurements of multiple auditory steady-state responses has never been investigated and needs verification in a population with known audiometric behavioral thresholds.; Multiple auditory-steady state responses were recorded in 15 normal-hearing subjects with bilateral simulated conductive hearing loss. Air-conduction thresholds were determined for 500, 1000, 2000, and 4000 Hz modulated stimuli, bilaterally and simultaneously using ASSR testing, and bilaterally and sequentially using behavioral testing. The results of this study indicate that the accuracy of ASSR in estimating AC thresholds when a conductive hearing loss is present is dependent on frequency. This effect of carrier frequency was noted in normal hearing subjects as well. Correlation coefficients were statistically significant (p<0.05) when plotting behavioral air-conduction thresholds as a function of ASSR air-conduction thresholds for test frequencies 500, 1000, 2000, and 4000 Hz for the right and left ear (0.689, 0.690, 0.825, and 0.907; 0.712, 0.712, 0.763, and 0.915).; Bone-conduction threshold estimates obtained using the SAL technique with behavioral and ASSR testing were established in the same 15 normal-hearing subjects with bilateral simulated conductive hearing loss and were compared to traditional BC thresholds. With the SAL technique, bone-conduction threshold estimates were determined by the degree to which the ASSR AC thresholds were masked by noise delivered via bone-conduction. Comb-filtered noise was utilized because it is effective in masking all 4 frequencies (500, 1000, 2000, & 4000 Hz), but is more efficient in doing so (decrease overall dB SPL), thus producing less artifact. No clear pattern or frequency range at which behavioral-SAL or ASSR-SAL BC thresholds were above or below traditional behavioral BC thresholds were found.; Air-bone gap estimates were calculated from the AC and BC threshold estimates measured from these 15 normal-hearing subjects with bilateral conductive hearing loss. The ABG estimates obtained using ASSR (ASSR AC - ASSR-SAL BC) proved to be more reliable than the Behavioral AC-Behavioral-SAL ABG estimates across the frequencies in the left ear, but not the right ear. Air-bone gaps obtained using ASSR AC thresholds and ASSR-SAL BC thresholds were significantly correlated with air-bone gap estimates obtained using traditional behavioral testing for all test frequencies for the right and left ears (0.782, 0.812, 0.828, and 0.923; 0.831, 0.833, 0.845, and 0.950). The application of the SAL technique with ASSR testing should be investigated more in depth in subjects with a true conductive hearing loss, mixed hearing loss, and sensorineural hearing loss, in addition, to looking at ASSR and the SAL technique in children. |
