There it is again, that little speck that glides across my vision from time to time, then disappears. There are times when I’m looking at the sky or a blank wall and notice little shapes floating in front of me. They’re not quite clear — almost like little bits of dust stuck on a camera lens. I try to blink them away, but they’re still there. When I look somewhere else, these shapes move with me. Mostly, it’s an annoyance and distraction, but sometimes it’s briefly entertaining to try to follow their path. But what are they, and where did they come from?

Major League Baseball is back, and so is the 100-mph fastball. How is a batter able to hit a ball traveling faster than the eye’s ability to track it? The answer lies with the retina’s ability to signal the brain to anticipate the future, or predictive motion encoding.