Your brain is faking all of it. The actual visual stimuli from your eye has far less bandwidth than you would think. Your brain builds a 3 dimensional internal representation of the world around you and is continuously updated part by part from your visual input. It's nothing like a computer monitor where all the pixels are being refreshed every single time.

In fact your ears will update the internal representation as well as your eyes. Your brain processes the sounds, directions, and timing of the sounds to help update your location within that representation.

Just how well your visual cortex understands the complex interaction of light on surfaces is truly amazing. There is a particular optical illusion that demonstrates how strong this knowledge of how light should work can influence what you believe is true.

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https://en.wikipedia.org/wiki/Checker_shadow_illusion

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Your brain INSISTS that A and B are different shades, because the rest of the checkerboard follows a consistent pattern, and part of it must be in shadow. It is one of those optical illusions that is nearly impossible to "turn off" because your visual cortex simply does this processing 100% of the time automatically.