Despite his mother beckoning him to come towards her, this infant hesitates to cross the "visual cliff" – an apparently steep drop that is actually covered by transparent glass. Psychologists in the 1960s found that most infants 6 to 14 months of age were reluctant to crawl over the cliff, suggesting they had the ability to perceive depth. Most psychologists believe that the ability to perceive depth is partly innate and partly a product of early visual experience.
Here's a test you can try to demonstrate how your perception of depth is still live and active. Below are two perfect circles, yet the smaller circle appears distorted. Our brain interprets the converging lines to be adding depth to the screen, as if the solid middle is further away from us than its perimeter. As a result, the circle appears warped the closer it gets to the middle, even though it is strictly a 2-dimensional image and no depth actually exists.
