Baseball players take note: animation has been used to analyse the slippery trajectory of curve balls.
Like a real baseball, the animated ball is spinning. It is also falling vertically. Viewers who look directly at it perceive it correctly as moving downwards, while those viewing it from the corner of their eye perceive it to be moving at an angle. This suggests that when we use our peripheral vision, the brain uses the internal motion of objects – in this case, spinning – as well as their overall direction to determine how an object is moving. In this case, it causes the ball to appear to move to the side.