Neural activity before and after conscious perception in dichotic listening.

The neural basis of conscious perception can be studied using stimuli that elicit different percepts on different occasions (multistable perception). Multistable perception allows direct comparisons between brain activity and conscious perception that control for sensory input, and also serves as a model for attentional competition, with the winning perceptual outcome varying across trials. Dichotic listening tasks present multistable stimuli consisting of two different consonant-vowels (CVs, one/ear). For each trial one ear usually conveys the dominant percept. We used EEG to measure neural activity before and after dichotic stimulus presentation to compare activity among left vs. right ear percepts and a control task. Consonant-vowels were perceived more often to the right vs. left ear. Pre-stimulus EEG power in the beta band (16-20 Hz) increased for left compared to right ear percepts and control trials. Event-related potentials after stimulus onset showed smaller P50 amplitudes ( approximately 50 ms latency) for left ear compared to right ear and control trials. Results indicate that neural activity for right ear percepts is comparable to control conditions, while activity for the atypical left ear percept differs before and after stimulus onset. Pre-stimulus EEG changes for left ear percepts may indicate a mechanism of spontaneous fluctuations in cortical networks that bias attentional competition during subsequent sensory processing. The P50 amplitude differences among perceived ears suggests that rapid sensory and/or arousal-related activities contribute to the content of conscious perception, possibly by biasing attentional competition away from the dominant right ear channel. Copyright (c) 2010 Elsevier Ltd. All rights reserved.