The independent influence of valence and arousal on emotional hemispheric  brain asymmetry was investigated to decide between three contrasting hypotheses:  the right hemisphere hypothesis, the valence hypothesis, and the integrative  hypothesis. Event-related potentials (ERPs) were recorded while participants (N  = 20) viewed positive high arousal, positive low arousal, negative high arousal,  and negative low arousal pictures, following a baseline measure of ERPs while  viewing gray squares. Self-ratings of emotional state in terms of valence and  arousal were taken after each of the four emotion blocks. Valence and arousal  effects on hemispheric asymmetry were analyzed for the time windows 130–170,  170–280, 280–450, and 450–600 ms. Right dominance on N2 during negative high  arousal and left dominance on P3 and late positive potentials during negative  low arousal were found over the frontal lobe. Right dominance on P2, P3, and  late positive potentials over the parietal lobes appeared during high arousal.  No frontal asymmetry was found in positive emotion. Our result partly supported  the integrative hypothesis and did not provide evidence for the right hemisphere  hypothesis or the valence hypothesis. These results suggested that arousal plays  the main role in the ERPs’hemispheric asymmetry.

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