Wideband reflectance acoustic reflex thresholds in normal ears of younger and older adults

Introduction. The purpose of the study was to evaluate wideband reflectance (WBR), in comparison with the traditional acoustic-immittance (AI) method for the measurement of contralateral acoustic reflex thresholds (CARTs) for the broadband noise (BBN) and 1000-Hz tonal activators in younger versus adults, and to examine the any aging effects on the WBR CARTs.;Methods. The WBR (Mimosa instrumentation with a 24-chirp probe stimulus and signal averaging of 16 responses) and AI BBN and 1000-Hz CARTs of 10 younger (20-30 years of age) and 10 older adult females (60-70 years of age) with essentially normal-hearing sensitivity were investigated.;Results. The WBR frequency-response graphs revealed a positive peak in the low-frequency region and a negative peak at a higher frequency region. Good test-retest reliability was obtained for the WBR CARTs in both groups. The mean 1000-Hz CART was slightly, but significantly higher for the WBR than AI approach in the younger adults, and was essentially the same for both approaches in the older adults. No significant age effect occurred for the WBR CARTs for either activator. The NTD was significantly larger with the WBR than AI approach in both age groups.;Discussion. In the frequency-response WBR graphs, the positive peak reflects increased energy reflectance by the middle ear; the negative peak reflects increased energy absorption into the middle ear. The significantly WBR than AI NTD suggests that the WBR rather than AI method should be used for NTD measurement for prediction of hearing sensitivity based on the CARTs, especially in older adults, in whom the traditional AI approach yields reduced NTDs. The significant improvement in the WBR BBN CARTs in comparison with the AI BBN CARTs may result from summation of the energy of the BBN activator and the chirp probe stimulus. Because the WBR approach yielded an expanded NTD that primarily is attributable to the improved WBR BBN CART as compared with the AI BBN CART and to the summation effect, future research needs to re-examine all other parameters of the acoustic reflex related to the BBN stimulus, such as latency, magnitude, and temporal integration and aging effects upon these parameters.