EEG and EMG responses to emotion-evoking stimuli processed without conscious awareness.

Dichotic stimulus pairs were constructed with one word that was emotionally neutral and another that evoked either negative or positive feelings. Temporal and spectral overlap between the members of each pair was so great that the two words fused into a single auditory percept. Subjects were consciously aware of hearing only one word from most pairs; sometimes the emotion-evoking word was heard consciously, other times the neutral word was heard consciously. Subjects were instructed to let their thoughts wander in response to the word they heard, during which time EEG alpha activity over left and right frontal regions, and muscle activity (EMG) in the corrugator ("frowning") and zygomatic ("smiling") regions were recorded. Both EEG and EMG provided evidence of emotion-specific responses to stimuli that were processed without conscious awareness. Moreover both suggested relatively greater right hemisphere activity with unconscious rather than conscious processing.