Hemispheric decoupling of awareness-related activity in human auditory cortex under informational masking and divided attention
The conditions under which sensory stimuli require selective attention to reach awareness is a fundamental question of cognitive neuroscience. We examined this question in the context of audition utilizing M/EEG and a dual-task informational-masking paradigm. Listeners performed a demanding primary task in one ear - detecting isochronous target-tone streams embedded in random multi-tone backgrounds and counting within-stream deviants - and retrospectively reported their awareness of secondary, masker-embedded target streams in the other ear. Irrespective of attention or ear, left-AC activity strongly covaried with target-stream detection starting as early as 50 ms post-stimulus. In contrast, right-AC activity was unmodulated by detection until later, and then only weakly. Thus, under certain conditions, human ACs can functionally decouple, such that one - here, right - is automatic and stimulus-driven while the other - here, left - supports perceptual and/or task demands, including basic perceptual awareness of nonverbal sound sequences.