The effects of aging and interaural delay on the detection of a break in the interaural correlation between two sounds.

OBJECTIVES: In noisy, reverberant environments, older adults often find it difficult to process acoustic signals, possibly because their ability to differentiate reflected waves that belong to a source from those generated by other sources diminishes with age. Therefore, older adults may be less efficient than younger adults at parsing the auditory scene into its component sound sources. To parse the auditory scene into its component sources the listener has to be able to group correlated waves coming from different directions (the direct wave and its reflections off of environmental surfaces). Because detecting a change in correlation is an important component of scene parsing, this study examined whether there is an age-related deficit in detecting break in correlation (BIC) between the noises presented over left and right headphones or over left and right loudspeakers, where a BIC refers to a change in interaural correlation from 1 to zero and then a return to 1.
DESIGN: In experiment 1, we determined the shortest BIC duration at which 10 younger and 10 older adults could detect the BIC in the middle of identical noises (bandwidth = 10 kHz; duration = 1 sec) presented simultaneously to the left and right ears over headphones or played simultaneously over loudspeakers positioned 45 degrees to the left and right of the listeners. In experiment 2, we determined the longest delay between the left-side noise and the right-side noise, at which a 100 ms BIC presented in the middle of the noise could be detected in 10 younger and 8 older adults.
RESULTS: The results of experiment 1 show that younger participants could detect significantly shorter BICs than older participants independent of whether the noises were presented over headphones or loudspeakers. The results of experiment 2 show that younger participants could detect the 100 ms BIC at significantly longer interaural delays than older participants. Also, for both age groups, detecting the BIC was easier under the loudspeaker-stimulation condition than the headphone-stimulation condition. Moreover, in the loudspeaker condition, the spectral cues arising from interactions between correlated sound sources seemed to be of greater benefit to younger than to older participants.
CONCLUSIONS: The age-related decrease in sensitivity to a BIC indicates that older adults are less able than younger adults to detect a change in correlation in an ongoing sound. The inability of older adults to detect the 100 ms BIC as readily as younger adults, when the noise arriving at one ear is delayed relative to the noise arriving at the other ear, suggests that the representation of aspects of the sound's waveform decays more rapidly in older adult than in younger adult listeners. Moreover, these age-related deficits are not related to listeners' audiograms. In addition, younger adults seem to be much better than older adults at using the spectral cue provided by comb filtering to detect the BIC when there is a delay between the noises presented over loudspeakers. The more rapid decay of waveform details, combined with the lesser sensitivity to change in correlation and to spectral cues, suggest that older adults may not be as capable as younger adults in parsing auditory scenes.