Abstract:
Audiologists are reliant on objective audiometric procedures to predict auditory sensitivity in difficult-to-test populations. A technique to estimate frequency-specific hearing thresholds in a time-efficient way for difficult-to-test populations, who are unable to provide behavioural responses, has long been the hope of audiologists. The auditory brainstem response (ABR) has dominated the field of objective electrophysiological audiometry for the past three decades. Although it provides a useful method of estimating auditory sensitivity, it presents with its own set of limitations. Recently the auditory steady state response (ASSR) has demonstrated promise of addressing the limitations of the ABR as it is an evoked response uniquely suited to frequency-specific measurement. An optimised version of the ASSR, the dichotic multiple frequency (MF) ASSR, has been proposed as a time-efficient way of evaluating different frequencies simultaneously in both ears. The aim of this study was to evaluate the clinical usefulness of the dichotic MF ASSR technique for estimating pure tone behavioural thresholds at 0.5, 1, 2, and 4 kHz, compared to a 0.5 kHz tone burst and broadband click ABR protocol in a sample of normal hearing adults (56 ears). A comparative experimental research design was selected in order to compare thresholds obtained with the different procedures. The results indicated that both the dichotic MF ASSR and a 0.5 kHz tone burst and broadband click ABR protocol provided a reasonable estimation of PT behavioural thresholds in a time-efficient manner for a group of normal hearing subjects. The click ABR did, however, present with 1, 2, and 4 kHz PT threshold estimations that were almost 50 % closer than that of the dichotic MF ASSR according to the mean and normal deviation. This increased accuracy and reliability of the click ABR is however compromised by its lack of frequency-specificity. In the low frequency region of 0.5 kHz, the tone burst ABR and dichotic MF ASSR evidenced estimations of the pure tone threshold that were, on average, very similar. The tone burst ABR, however, presented with a mean threshold slightly (3 dB) closer to the pure tone threshold than the dichotic MF ASSR. The 0.5 kHz dichotic MF ASSR presented with a smaller range of normal deviation in the estimation of pure tone thresholds which suggested a more reliable measure than the 0.5 kHz tone burst ABR. The dichotic MF ASSR evaluation provided eight thresholds (4/ear) in 23 minutes on average compared to 25 minutes on average required by the ABR protocol to evaluate 4 thresholds (2/ear). This research concluded that the dichotic MF ASSR is useful for estimating frequency-specific pure tone thresholds reasonably well in a time-efficient manner but that this technique should be used in a test-battery alongside the ABR. Both the dichotic MF ASSR and the ABR comprise unique qualities that can be combined in a cross-check principle approach in order to provide complementary information that will verify results obtained with each procedure.
