Why is the study of perception so appealing? One reason is that you can gain deep insights into the inner workings of your own brain by doing relatively simple experiments that any schoolchild could have done 100 years ago. More on those in a moment.

Your sensory experience of the world does not involve faithfully transmitting the retinal image to a screen in the brain so that it can be "seen" by some inner eye. One piece of evidence for this fact is that your perception of an object (a; two faces or a goblet?) can change radically even if the image on the retina is held constant, which implies that even the simplest act of observation involves judgment by the brain.

This article was originally published with the title Stability of the Visual World.

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