Realistic interaural level differences help listeners suppress auditory distractors

Past research hints that realistic auditory spatial simulations not only “sound better,” but better engage brain mechanisms controlling spatial auditory attention. We sought to replicate this finding by comparing behavior and neural responses for simulations using: (1) individualized head-related transfer functions (HRTFs), (2) filters preserving individualized, frequency-specific interaural level differences (ILDs) but removing interaural time differences (ITDs), and (3) filters preserving ITDs but removing ILDs. Listeners were asked to report back a random stream of consonant-vowel syllables (tokens spoken by a male talker) from left or right while ignoring a different random, temporally inter-digitated consonant-vowel stream from the opposite direction. To extend previous findings, we tested a listener’s ability to ignore a salient distinct sound (a cat MEOW) that occurred in the middle of some randomly selected trials. ITD-only simulations led to worse performance, especially on cat-interrupted trials. Simultaneous electroencephalography showed that in ITD-only simulations, attention evoked no significant lateralized alpha oscillations (a signature of spatially directed attention) and the to-be-ignored cat elicited larger neural responses than for other simulations. These results highlight how different auditory virtual environment simulations can influence perceptual and neural outcomes and suggest that simulations including natural ILDs enhance a listener’s ability to focus spatial attention.