Interaural time difference sensitivity as a function of interaural coherence in the aging auditory system

Interaural time difference (ITD) cues are the dominant cue for sound localization in the horizontal plane. Encoding of ITD is postulated to occur via an internal binaural cross-correlation function, where the peak correlation serves as the interaural coherence (IAC) and the delay in which the peak occurs serves as the ITD. Sound sources in anechoic chambers have IAC values at or near 1. Sound sources in reverberant rooms have a wide range of frequency-dependent IAC values between 1 and 0, where ITD sensitivity decreases as IAC decreases toward 0 [Rakerd and Hartmann, J. Acoust. Soc. Am. 28, 3052–3063 (2010)]. The current work builds upon the relationships described by Rakerd and Hartmann to examine the degraded binaural temporal processing of the aging auditory system in complex (reverberant and noise-filled) rooms. Behavioral ITD thresholds were measured as a function of IAC for younger and older listeners with clinically normal hearing. Results indicate that at higher IAC values, older listeners have elevated ITD thresholds. However, at lower IAC values, ITD thresholds between listener groups converge. Following Rakerd and Hartmann, binaural analyses were made in a reverberant room, with the addition of competing noise to simulate listening scenarios older listeners often find difficult.