Fun fact? Our eyes actually see the world upside down. The way that our eyes refract light means that the signal literally coming in the wrong way to our brains. Our brains “correct” the signal to make sure that we see everything the “right” way. Without the mind, we would be walking on the ceiling.
So, naturally, someone wanted to see if there was a way to reverse this. Theodor Erismann (to be precise about the name) and his student Ivo Kohler gave people glasses that flipped their vision again, so that for days they were viewing the world upside down again. But the funny thing? Their vision adapted–that is, around the fourth day, the image coming from the upside-down glasses and the upside-down eyes was turned right-side up. Their brains shifted.
Through all of this, “reality,” that is, the external world, didn’t change. Perception did.