Also curious how it flips what we see and how it knows to do that, or why it’s possible to see anything upside-down at all.
In: Biology
On the back of our eye is our retina, which contains the cells that detect light and pass those signals to our brain. Let’s first imagine that our eyes were just open sockets with the retina on the back. Light would hit the cells in the retina from all directions, so each light detector would be getting light from everywhere, and it would be impossible to distinguish which light was coming from which direction, so there’d be no way to form an image.
Because the light passes through a tiny hole (our pupil), this filters the light so that each light detector on our retina is only receiving light from a specific direction, and thus an image can be interpreted. This is exactly how cameras work, too. But if you imagine a light ray coming from above us, it would be entering our eye on a downward direction, so it would hit the bottom area of our retina, and vice versa for light rays coming from below us. So the image is actually hitting our retina upside-down (and mirrored left-right).
The detectors in our retina are wired to our brain such that the bottom detectors are interpreted as the top of our eyesight, the left is interpreted as our right, etc. I wouldn’t say that our brain actually sees things upside-down, it’s just that the image hits our retina upside-down, but is wired into our brain so that we interpret it correctly.
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