Contributions of stimulus valence and arousal to visual activation during emotional perception

Neuroimaging experiments have revealed that the visual cortex is involved in the processing of affective stimuli: seeing emotional pictures leads to greater activation than seeing neutral ones. It is unclear, however, whether such differential activation is due to stimulus valence or whether the results are confounded by arousal level. In order to investigate the contributions of valence and arousal to visual activation, we created a new category of "interesting" stimuli designed to have high arousal, but neutral valence, and employed standard neutral, unpleasant, and pleasant picture categories. Arousal ratings for pleasant and neutral pictures were equivalent, as were valence ratings for interesting and neutral pictures. Differential activation for conditions matched for arousal (pleasant vs neutral) as well as matched for valence (interesting vs neutral) indicated that both stimulus valence and arousal contributed to visual activation.