When judging whether shaded images are convex or concave, adult brains assume that light comes from above unless there is reason to think otherwise. Young children have to learn this ability.
To investigate when this happens, Jim Stone at the University of Sheffield, UK, showed embossed shapes such as squares and shaded images such as footprints to 171 children aged from 4 to 10. Each child was shown 10 images and asked whether they were convex or concave. The “correct” answer assumed an object was lit from above.
The children got better with age, with the average score out of 10 improving by 0.43 each year (Perception, DOI: 10.1068/p6725). If children of other ages develop at the same rate, Stone predicts that babies will learn to assume that light comes from above at about 21 months. But this aspect of their visual perception won’t be “fully grown” until the age of 13 or so.
“Children really do see the world differently to adults, inasmuch as their perceptions seem to be more variable,” says Stone. “No wonder they can’t look at a cloud without seeing a dog or a bear.”