No pitcher can make a curveball “break” or a fastball “rise.” What hitters—and fans—think they see is simply an illusion, new research shows.
Led by Arthur Shapiro of American University and Zhong-Lin Lu of the University of Southern California, the researchers explain the illusion of the curveball’s break in a publicly available study in the journal PLoS ONE.
The study comes a year after the same group won the prize for best illusion at the Vision Sciences annual meeting with a demonstration of how an object falling in a straight line can seem to change direction. That demonstration led to debates among baseball fans over the existence of the break in curveballs, breaking balls, and sliders.
USC College Professor of Psychology Zhong-Lin Lu proposed that the "break" in a curveball that fools some batters is a visual illusion. "Curveballs do curve," Lu says, but in a conversation with USC Pitching Coach Tom House, he explains why a perception of a sudden drop or other change in trajectory is a trick of the eye. This study was published in the scientific journal PLoS ONE. To read the whole story, please go to: http://uscnews.usc.edu/science_techno... Video by Mira Zimet and Zane Fried.
The PLoS ONE study explains the illusion and relates the perceived size of the break to the shifting of the batter’s eye between central and peripheral vision.
“If the batter takes his eye off the ball by 10 degrees, the size of the break is about one foot,” Lu said.
He explained that batters tend to switch from central to peripheral vision when the ball is about 20 feet away, or two-thirds of the way to home plate.
The eye’s peripheral vision lacks the ability to separate the motions of the spinning ball, Lu said. In particular, it gets confused by the combination of the ball’s velocity and spin.
The result is a gap between the ball’s trajectory and the path as perceived by the batter.
The gap is small when the batter switches to peripheral vision, but gets larger as the ball travels the last 20 feet to home plate.
As the ball arrives at the plate, the batter switches back to central vision and sees it in a different spot than expected.
That perception of an abrupt change is the “break” in the curveball that frustrates batters.
“Depending on how much and when the batter’s eyes shift while tracking the ball, you can actually get a sizable break,” Lu said. “The difference between central and peripheral vision is key to understanding the break of the curveball.”