Minimum Audible Angle and the Acoustic Change Complex Elicited by Azimuthal Shifts in Low-Frequency Sounds: Effects of Age.

This study compared the behavioral minimum audible angle (MAA) and the electrophysiological acoustic change complex (ACC) elicited by an azimuthal shift in sound location. To examine age effects, 63 participants with normal or near-normal hearing were divided into three age groups (Young, Mid-Aged, and Older). The stimuli were narrow bands of noise centered at 500 Hz to facilitate reliance on primarily binaural temporal cues. Putative spatial location was manipulated by means of head-related transfer functions under headphones. MAA results showed that performance was dependent on the reference location, with performance becoming poorer as the reference location shifted away from midline. The Young group had smaller MAAs than the Older group, and performance of the Mid-Age group was intermediate. Measurement of the ACC was restricted to shifts away from midline, and results showed no ACC for shifts of 4.5° and 9° but present ACCs for shifts of 13.5°, 18°, and 36°. The robustness of the ACC, as measured with the intertrial phase coherence metric, grew with increasing azimuthal shift. For shifts of 13.5° and 18°, Young participants had more robust ACCs than Older participants. Although age-related deficits were found in both the MAA and in the robustness of the ACC, no associations were observed at the individual level between MAA and ACC measures. Further work is necessary to evaluate the ACC elicited by shifts from off-midline reference locations before a firm conclusion can be reached that the ACC is not a viable objective proxy for the MAA.