Scientist Throws Curve Into Breaking-Ball Debate

FRIDAY Oct. 30, 2009 -- The ball flies out of the pitcher's hand. In less than a second, it curves and then drops, baffling the batter.

Or does it?

The curveball, when thrown correctly, is one of baseball's most daunting pitches. For more than a century, batters great and not so great have sworn that the ball seems to have a life of its own.

But now, a California cognitive neuroscientist has resurrected the timeless debate -- just in time for the Yankees-Phillies World Series showdown -- over whether the curveball is real or, in fact, an optical illusion that does not "break" before the hitter can whack it.

"Physically, there is no such thing as a breaking curveball," said Zhong-Lin Lu, who holds the William M. Keck Chair in Cognitive Neuroscience at the University of Southern California, in Los Angeles. "It's mostly in the hitter's mind."

According to Lu, who helped to design a popular Web animation that illustrates the science behind what he calls the curveball illusion, the ball travels relatively straight toward the batter, curving somewhat but not nearly as much as claimed. What causes the perception of the break is a complex interplay between the fast spin of the ball, the contrast between the ball's red seams and white background, and the batter's flawed visual perception as the ball nears the plate.

Here's how the curveball phenomenon seems to work, said Lu, a visual motion and perception specialist:

The ball leaves the pitcher's arm at approximately 75 mph, slower than an average fastball. While it hurtles toward the batter, the ball spins obliquely at around 1,500 rpm (or 25 rotations per second). The ball reaches the plate in about 0.6 seconds.

Because of its unique spin, the ball appears to be moving faster than it really is, causing the batter to overestimate the speed. A slight curving trajectory forces the ball to move somewhat away from the hitter's frontal view toward his side -- or peripheral -- vision just before he swings.

It's during this final shifting of perception from frontal (also known as foveal) to peripheral view that causes the batter to perceive that the ball is dramatically dropping or moving abruptly to the left or right. In fact, the curveball is moving relatively straight, Lu said.

"The greater your eyes move away from the ball, the greater the curve," he said.

Lu demonstrated the illusion by creating a simple animation with the help of Arthur Shapiro, associate professor of psychology at American University, and other collaborators. The demonstration won the Best Visual Illusion of the Year prize at the Vision Sciences Society meeting in Naples, Fla., last spring.

In the graphic, a spinning ball moves from top to bottom. If the viewer keeps his or her gaze directly on the object, it appears to be traveling straight. It is only when the viewer shifts his or her gaze to a large, stationary blue dot on the side of the graphic that the moving ball appears to quickly veer off course.

As elegant as Lu's graphic is, not everyone agrees with him, including former star Major League Baseball pitcher Mike Marshall.

"I can't believe the guy is saying something that was disproved almost 50 years ago," said Marshall, of Florida, who won a Cy Young Award, baseball's highest pitching honor, in 1974. "It's absolutely ridiculous."

Marshall, who majored in exercise physiology while earning a doctorate at Michigan State University, said a curveball isn't a trick of the eye. Its trademark movement is due to air pressure forcing the spinning ball downward. If there is a faulty visual perception, batters tend to learn fast and compensate for it, he said.

"Baseballs move. They really move," Marshall said.

Freddy Berowski, a researcher at the National Baseball Hall of Fame in Cooperstown, N.Y., struck a more philosophical tone.

"There seem to be arguments on both sides," he said. "But what really matters is that the batter thinks it curves."

More information

To view Lu's curveball demonstration video click here.

Posted: October 2009


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