Jul 16, 2009

# Optical Illusion of the Year: The Break of a Curveball

Taking first prize at the Best Visual Illusion of the Year Contest held this past May, The Break of the Curveball submission does a fantastic job portraying a concept that you have to see to believe.

Anatomy of the Curve

– In the game of baseball, a pitcher stands on a mound and throws a 2.9-inch diameter ball in the direction of home plate
– A typical major league curveball travels at about 75 mph, and spins at an oblique angle at about 1500 rpm; this means that the travel time from the pitcher’s hand to home plate is about 0.6 sec, during which time the ball undergoes about 13 rotations
– The spinning of the curveball creates both a physical effect (“the curve”) and a perceptual puzzle
– The curve arises because the ball’s rotation creates an imbalance of forces on different sides of the ball, which leads to a substantial deflection in the path of the ball
– The perceptual puzzle arises because the deflection of the ball should appear gradual, but from the point of view of the batter standing near home plate, the flight of the ball often appears to undergo a dramatic and nearly discontinuous shift in position (this sudden shift is referred to as the curveball’s “break”)

This concept kind of makes sense but you need to see it, right?

Well check out the submission below from Arthur Shapiro, Zhong-Lin Lu, Emily Knight, & Robert Ennis!

The Break

1. When the batter tracks the ball foveally, the motion will follow the oval (i.e., the ball appears to
descend vertically)
2. When the batterer fixates to the right of the screen so that the ball falls in the far periphery, the ball appears to drift down the screen at an oblique angle
3. When the batter initially fixates to the right of the screen (i.e., viewing the ball in the periphery) and
then, in the middle of the ball’s descent, shifts his/her gaze to look directly at the ball (so that the oval is
in the fovea), the flight of the ball “snaps” suddenly from an oblique to a vertical descent.

The dramatic shift in direction seen in step 3 is the ‘break’. The shift between objects in our fovea and periphery is the root cause of this type of visual illusion. Cool!

For a more detailed explanation straight form the source, please click here
For a PDF of the Curveball Illusion contest submission, please click here

Now let’s take a look at a curveball in real life, nasty stuff: