The Situation of the “Curveball”
Posted by The Situationist Staff on November 1, 2009
From U.S. News:
“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.
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Zhong-Lin Lu, a professor of cognitive neuroscience at USC, along with USC alumni Emily Knight and Robert Ennis and Arthur Shapiro, associate professor of psychology at American University, developed a simple visual demo that suggests a curveball’s break is, at least in part, a trick of the eye.
Their demo, viewable at outstanding Illusion Sciences blog (here), won the Best Visual Illusion of the Year prize at the Vision Sciences meeting earlier this year.
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To read a sample of related Situationist posts, see “Jim Rice and the Situation of Baseball Hall of Fame Voting,” “Big Papi Magic,” “The Situation of a Baseball Pitch,” “The Batting Situation,” and “The Unconscious Genius of Baseball Players.” To review other Situationist posts containing of discussing illusions, click here. Finally, to review a collection of similarly fascinating illusions by Arthur Shapiro, go to Illusion Sciences Blog.