Interactions between "light-from-above" and convexity priors in visual development.

Having a prior assumption about where light originates can disambiguate perceptual scenarios. Previous studies have reported that adult observers use a "light-from-above" prior as well as a convexity prior to constrain perception of shape from shading. Such priors may reflect information acquired about the visual world, where objects tend to be convex and light tends to come from above. In the current study, 4- to 12-year-olds and adults made convex/concave judgements for a shaded "polo mint" stimulus. Their judgments indicated an interaction between a "light-from-above" prior and a convexity prior that changed over the course of development. Overall, observers preferred to interpret the stimulus as lit from above and as mostly convex. However, when these assumptions conflicted, younger children assumed convexity, whereas older groups assumed a light from above. These results show that both priors develop early but are reweighted during childhood. A convexity prior dominates initially, while a "light-from-above" prior dominates later and in adulthood. This may be because convexity can be judged relative to the body, whereas judging the direction of light in the world requires the use of an external frame of reference.