A psychologist from the 19th century called George Malcolm Stratton wanted to see what would happen if the
brain, normally receiving images formed in the retina upside down, received images the right way up.
So he did some experiments to test that. One of them was wearing special reversing glasses (more like goggles) for almost 3 days (21 hours). But nothing happened, apart from his seeing the world upside-down and feeling extremely “awkward” during that time. When he removed the glasses, his vision was normal again.
“Stratton, G. (1896). Some preliminary experiments on vision without inversion of the retinal image. Psychological Review, 3.”
After that, he wore the glasses for 8 days in a row. When he arrived to the 4th day, he increasingly saw things
upright instead of inverted. And then he noticed that only when he concentrated on the particular images, he saw them inverted again. When he finally removed the glasses, it took his brain some days to get back to normal, so in the meantime he saw things inverted again. Because his brain had adapted to the inversion, he saw things upright when he wore the glasses but inverted when he stopped wearing them.
Conclusion: “it takes the brain three days to adapt”.
Stratton, G. (1897).Vision without inversion of the retinal image. Psychological Review, 4.