The sharp break that sluggers see as a curveball reaches the plate springs from our brains overinterpreting the spin on the ball, visual experts say.
In essence, curveballs take a batter's peripheral vision for a spin, says a new study on the topic in the journal PloS One.
Keeping your eye on the ball remains the best advice.
"The more you keep the ball in focus, the better off you'll be," says American University psychologist Arthur Shapiro, who led the small study. "Our peripheral vision is not just a blurry version of our central vision."
Scholars have enjoyed the curveball almost as long as baseball fans, demonstrating the ball really does curve, a matter of nationwide debate in the 1940s and 1950s.
"The ball really follows a smooth curved path, so why do batters sometimes look so foolish swinging at them?" asks study co-author Zhong-Lin Lu of the University of Southern California, an expert on peripheral vision.
In the study, five volunteers witnessed a computer simulation of what batters see facing a curveball.
Until the ball is about 20 feet from the plate, they focused on the ball with their central vision, then handed off the ball to their peripheral eyesight.
What the study suggests is that brain cells that process peripheral vision displace spinning objects in the direction of their rotations.
"The break in a pitch comes in the last five feet of the pitch, when your central vision takes over again, and the ball snaps back to its true location as your swing passes over it," Lu says.
Says University of Illinois physicist Alan Nathan: "They might have an interesting explanation for the effect, but I don't see how this will help batters."
A major league pitch takes less than 0.4 seconds to travel the 60 feet, 6 inches from the from pitcher's mound to the catcher's mitt, Nathan says.
Batters must make up their minds to hit the ball long before the ball approaches within 20 feet of the plate.
But Lu and Harris suggest that batters could likely be trained out of the habit of letting their peripheral vision fool them.
"The best physical device with which to test the curveball illusion are baseball batters batting against baseball pitchers in competitive games," kinesiologist Mike Marshall, a former major league player (an excellent relief pitcher for several years with the Los Angeles Dodgers), says via e-mail.
"After baseball batters watch baseball pitchers throw curves, they learn to correctly anticipate when baseball pitchers will throw their curves."