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 resea
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