How can our eyes tell the difference between a close object and a far object
In: Biology
It’s mostly your brain doing it, not your eyes. /u/OccassionalReddit194 described it well.
A lot of people think it is just because we have two eyes and hence a slightly different view from each eye. That really only works for things that are quite close. For distant objects, it’s pretty much useless, since both eyes get the same view. You can easily test this yourself. Cover one eye and look around. Can you tell what is close and what is far? Yes, you can.
Lens focusing is a pretty minor part of it. People with artificial lenses in their eyes (which do not change focus) can perceive close/far objects just fine. Many people have artificial lenses to cure cataracts (me, for example).
Most of the work is done by your brain. You are constantly updating a model of your environment, figuring out what is close and what is far. Your brain does this in a variety of ways, such as seeing what objects obscure the view of others. But it relies on experience to a great deal.
Interestingly, your brain doesn’t keep an exact “image” of things to make this map. It seems to have a more abstract model to let you know just enough about the things that you aren’t actively looking at and concentrating on. Presumably that limits how much “processing power” or memory you need to be aware of your environment, freeing up your brain to do other tasks.
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