If you've ever seen something spooky out of the corner of your eye, then turned to see nothing there, you know that sometimes our peripheral vision just isn't that accurate. As Psychology Today explains, each eye has a blind spot about 18 degrees to either side. Our brain compensates for what our peripheral vision can't see,"[making] educated guesses about what we’re looking at, and its editing is highly biased by expectations, history, context, and desires." The problem is, sometimes these guesses are wrong, and we think we see things that aren't really there — and some scientists say that "ghosts" can be explained by these wrong guesses.