curveball2

In baseball, a curveball creates a physical effect and a perceptual puzzle. The physical effect (the curve) arises because the ball’s rotation leads to a deflection in the ball’s path. The perceptual puzzle arises because the deflection is actually gradual but is often perceived as an abrupt change in direction (the break).

USC (US)—The answer to the question of whose curveball breaks harder—that of the Yankees’ A.J. Burnett or the Phillies’ Cole Hamels—may be neither.

Zhong-Lin Lu, a professor of cognitive neuroscience at the University of Southern California, 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.

The idea is that the effect is due to the batters being forced to switch between peripheral vision and central vision during a swing.

Their demo won the Best Visual Illusion of the Year prize at the Vision Sciences meeting earlier this year.

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