Explaining the curvature effect: perceptual and hedonic evaluations of visual contour

Preference for curvature, the curvature effect, seems to transcend cultures, species, and stimulus kinds. However, its nature and psychological mechanisms remain obscure because studies often overlook the complexity of contour characterization and disregard personal and contextual factors. To investigate the curvature effect, we propose a continuous and multidimensional manipulation and contrasting experimental conditions examined at the group and individual levels that unveil a complex picture, not reducible to monotonous relationships: Perceptual and hedonic evaluations relied on multiple geometric features defining contour and shape. These features were specifically weighted to characterize each construct, depending on the individual and contingent on whether evaluating perceptually or hedonically. Crucially, the curvature effect was not robust to preference with respect to the median and continuous manipulations of contour for varying shapes. As curved contours are more easily perceived and processed than polygons, we hypothesized that perceived contour might explain liking for a figure beyond the effect of geometric features, finding that this association was subordinated to shape categorizations. Finally, domain-specific, personality, and cognitive-preference traits moderated how people used each geometric feature in their perceptual and hedonic evaluations. We conclude that research on perception and appreciation of contour and shape should factor in their complexity and defining features. Additionally, embracing individual sensitivities opens potential avenues to advance the understanding of psychological phenomena. In summary, our approach unpacks a complex picture of contour preference that prompts critical reflections on past research and advice for future research, and it is applicable to other psychological constructs.