PURPOSE: Visual information may convey different affective valence, and induce our brain into different cognitive status. Many studies have found that unpleasant stimuli could produce stronger emotional responses than pleasant stimuli. Although there has been notion that triangle with sharp corners is perceived as negative and circle consists of smooth curve as positive, there has been no systematic study to map the degrees of valence of stimuli with different cognitive status.
METHODS: We employed different shapes (ellipse and triangle, line drawn happy and angry faces for EEG; circle, triangle, ellipse, pentagon for fMRI) as visual stimuli to investigate the event-related-potential (ERP), and the brain functional patterns associating with cognitive ease and cognitive strain. The data of 19 subjects were selected for analysis.
RESULTS: Our behavioral results showed that reaction time for angry face was significantly shorter than those for happy face, triangle and ellipse (p<.05). In the ERP results, P1, N1, P2 and N2 amplitudes for angry face were significantly larger than those for happy face. Similarly, P1, N1, P2 and N2 amplitudes for triangle were significantly larger than those for ellipse. Particularly, P1 amplitude for angry face was the strongest, followed by happy face, triangle and ellipse in parietal lobe. The fMRI data showed that with second level group comparison, stronger activation was detected for shapes with corners (triangle and pentagon) in parietal lobe than circular shapes, especially, the comparison between circle and pentagon (p<.001). However, the brain activation with triangle was not significantly enhanced compared to that with circle.
CONCLUSIONS: This study has supported and extended the hypothesis that shapes inducing cognitive strain would lead to stronger neural responses than cognitive ease, and stronger affective stimuli induce larger responses than mild affective stimuli.