The processing of illusory contours demonstrates nicely how our visual system constructs what we see. Lower stages of processing become active first in detecting simple features of an image. But, these neurons do not "know" to which objects the detected edges, such as the mouths of the pac-men belong. Only the higher stages of the visual system are able to achieve this task and are first in detecting complex objects. In this regard, these higher stages act as the foremen directing the construction of perception and using feedback to lower stages to perhaps refine the perceptions we ultimately experience. The magic of illusions is not so much in what we perceive (though that is in itself pretty cool), but rather in how they show off the capacity of our brains to shape perceptions.

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