The Role of Local and Global Symmetry in Pleasure, Interest, and Complexity Judgments of Natural Scenes

Symmetry generally makes stimuli less complex, and symmetric arrangements are also generally preferred to asymmetric ones. Here, we investigated the roles of both local and global symmetry in subjective judgments of natural scenes. We collected ratings of complexity, aesthetic pleasure, and interest for 720 scene images and calculated average ratings for each image, as well as several measures of local and global symmetry. Global symmetry measures were calculated by creating an axis of symmetry at every column (vertical) and row (horizontal) of the grayscale image and correlating the rows or columns of pixels on either side of the symmetry axis, weighted by the proportion of pixels included in the correlation. Local symmetry measures were computed by converting each photograph into a line drawing and calculating the parallelism (ribbon symmetry) and distance (separation) between contours. To investigate the relationship between symmetry and participants' ratings, we ran a canonical correlation analysis using 12 symmetry measures as predictors of the three subjective rating measures. The analysis revealed two significant and interpretable canonical roots. In the first root, local symmetry and vertical global symmetry were negatively related to complexity, aesthetic pleasure, and interest (i.e., symmetry reduces complexity and renders the scene boring and unpleasant). Conversely, in the second root, local symmetry and horizontal global symmetry were positively related to pleasure and interest. Our work reveals the distinct roles of global and local symmetry in perceptual judgments and lends further support to the pleasure-interest model of aesthetic liking.