The effects of arousal and valence on facial electromyographic asymmetry during blocked picture viewing.

The effect of stimulus valence and arousal on facial electromyographic (EMG) asymmetry was investigated to inform the debate about two contrasting hypotheses of emotion: the right hemisphere dominance hypothesis and the valence hypothesis. EMG was recorded from the left and right corrugator and zygomaticus muscles while participants (N = 21) viewed blocks of negative and positive pictures that were high or low in arousal. Ratings of valence and arousal were taken before and after each of the four emotion blocks. Corrugator muscle activity yielded evidence for left hemi-face dominance during high and low arousal negative picture blocks whereas zygomaticus muscle activity yielded evidence for right hemi-face dominance during high arousal positive picture blocks, especially early during the picture sequence. This pattern of results is consistent with the valence hypothesis.