Symmetry perception and affective responses: a combined EEG/EMG study.

The perception and appreciation of visual symmetry have been studied in several recent EEG experiments. Although symmetry is known to be an important determinant of aesthetic preference, previous studies have concluded that evaluation does not occur spontaneously. These studies also found that symmetrical and random patterns do not differ in terms of early sensory processing, within 200ms of stimulus onset. We presented participants with symmetrical or random abstract patterns, which they had to classify correctly. Contrary to previous work, we found that N1 amplitude was sensitive to all types of regularity, and P1 was sensitive to rotational symmetry. We also found that activity in the Zygomaticus Major, the facial muscle responsible for smiling, was greater for reflection patterns. However, we were able to reverse this effect by changing the task so that participants had to treat random patterns as the target stimuli. We conclude that participants spontaneously select reflectional symmetry as the target, and positive affective responses automatically follow from successful target detection. This work provides a new account of the neural mechanisms involved in visual symmetry perception.