Electrophysiologic and Behavioral Masking Level Differences in Young and Older Listeners

Purpose: Many older adults have hearing loss and poor speech understanding. Poor synchrony in auditory nerves may be a factor. The behavioral masking level difference (vMLD) has been used to evaluate temporal processing, but study results vary. Behavioral tests are limited in studies of neural function. We used both the vMLD and the electrophysiologic masking level difference (eMLD) to investigate age-related hearing loss (ARHL), particularly by evaluating its peripheral and central components. Method: The masking level difference (MLD) is a binaural test measured as the difference in dB between the thresholds of SoNo (tones in phase between ears) and SπNo (tones out of phase between ears) in background noise. The dB difference between the two thresholds is the MLD. This study evaluated the effects of age and ARHL on the vMLD elicited from behavioral responses and the eMLD elicited from the electrophysiologic auditory late latency response potential P2. The four participant groups included 11 young adults tested with normal hearing, 11 young adults with simulated ARHL, 11 older adults with near-normal hearing, and 11 older adults with natural ARHL. Tests focused on the effects of age, hearing ability, and test method on the MLDs. Results and Conclusions: All participants had MLDs for all test conditions. Younger groups had larger MLDs compared with older groups. The interaction of age and test method showed that the smallest MLDs were for the older groups. The effect of age showed that the two older groups had significantly smaller eMLDs compared with the younger groups. The effects of test method were not significantly different for the younger groups. ARHL contributed minor effects (~2 dB to the size of both eMLDs and vMLDs). These results suggest that the ability to process out-of-phase signals declined with age. The eMLD is more sensitive to temporal processing deficits compared with the traditional vMLD.