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Why curveballs are so hard to hit

I’ve always found optical illusions fascinating, partly because they’re a good reminder that we can’t always believe the information we’re taking in.

I’ve always found optical illusions fascinating, partly because they’re a good reminder that we can’t always believe the information we’re taking in. Our eyes — and brains — can easily play tricks on us.

This year’s winner of the Visual Illusion of the Year contest, announced last month by the Neural Correlate Society, was “The Break of the Curveball.”

As MinnPost’s baseball fans already know, the curveball — a pitch that made former Twins pitcher (and current Twins announcer) Bert Blyleven famous — is notoriously iffy to hit.

Although typically slower than a fastball, the curveball has a spin that causes it to gradually curve as it approaches home plate, only to suddenly “break” at the last moment, often leaving the batter swinging at air.

Check out the winning curveball illusion here, along with the explanation by one of its creators, psychologist Arthur Shapiro, now at American University in Washington, D.C.

Another angle?
Is Shapiro’s explanation of the illusion of the curveball correct? I asked Robert Miller, MD, a professor of neuroscience at the University of Minnesota. He’s not so sure.

“It’s an interesting and fascinating illusion,” he says, “but like all illusions, there is always a controversy about how to explain them.”

Miller doesn’t believe peripheral vision plays much of a part in a batter’s struggle to hit a curveball. “It seems unlikely that the batter is using anything other than his fovea,” he says.

The fovea is the tiny pit in the retina (the layer of nerves at the back of the eye) that we use when we want to bring anything into sharp focus — the print on a computer page, a nail we’re hammering or a baseball hurling toward us. Peripheral vision is the vision that occurs outside this central gaze.

Jumping the gun
But Miller does agree that the two different motions of the curveball — the spin and the drop — are combining to confuse the retina as to where the ball really is.

The retina tends to jump the gun when it sees a moving object, he explains. It’s always trying to predict a split-second ahead of time where an object is going to end up — and for a good evolutionary reason. We humans have always needed to be able to dart out of the pathway of life-threatening objects — a falling rock, a poisoned spear, a pouncing tiger.

“When a baseball is thrown at, say, 100 miles an hour, the batter has about 500 milliseconds to perceive the direction in which the ball is moving and then initiate all the motor mechanisms needed to swing the bat,” says Miller.

If the retina “guesses” wrong about the ball’s eventual ending-up point – as it can easily do with a well-thrown breaking curveball – the result is a strike, not a hit. Just ask all those batters who struck out against Blyleven.

More illusions
If you want to check out more optical illusions (and remind yourself why it’s always good to have a skeptical mind about your perception of reality), try this site.