The Illusion of the Year contest was awarded to work done on the break on curveballs.
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). Our illusions suggest that the perceived “break” may be caused by the transition from the central visual system to the peripheral visual system. Like a curveball, the spinning disks in the illusions appear to abruptly change direction when an observer switches from foveal to peripheral viewing.
Unforntunately, the actual illusion can’t be embedded, but it’s worth checking out if you’ve ever played baseball or are remotely curious on the baffling pitch.