The Curvature Effect

Empirical work on visual aesthetics has found a strong preference for smooth curvature. The use of different tasks and exposures can clarify whether such a preference reflects immediate visual responses or higher cognitive processes, such as semantic associations. In three experiments, we used abstract irregular shapes and manipulated the contour (polygons vs. smoothed versions of polygons) but matched the stimuli for number of protrusions (vertices or curvature extrema) and number of concavities. In Experiment 1, shapes were presented for 120 ms, and observers produced a two-alternative forced-choice response (like or dislike). In Experiments 2 and 3, we used rating scales measuring liking and attractiveness, respectively, and the stimuli were presented until a response was made. Overall, smooth curved contours were preferred over angular contours, especially with immediate responses (Experiment 1). Moreover, shapes were preferred when they contained a balance between number of vertices and concavities (i.e., a lower proportion of concavities for a large number of vertices). However, a preference for shapes with the highest number of vertices and the least number of concavities occurred in the two-alternative forced-choice task (Experiment 1). In contrast, the reverse combination (i.e., star-like shapes) emerged with rating scales (Experiments 2 and 3). We conclude that the curvature effect is stable across tasks, although it is modulated subtly by some parametric variations (vertices and concavities) related to visual complexity.