Does The Ball Fall Straight Down or Does it Zigzag?

Zigzag Curveball

Look directly at the ball and it falls straight down.
Look to the side and the ball zigzags down the screen.

Demo and comment: https://t.co/GWLoxO5lUl#Illusions #Illusion #PeripheralVisionIsCool pic.twitter.com/v5vDXX536N

— Arthur Shapiro (@agshapiro2) June 17, 2019

Take a look at this Zigzag Curveball illusion - is the ball falling down straight or does it zigzag down the screen?

The answer depends on whether you're looking at it straight on, or to the side.

Arthur Shapiro explains:

The ZigZag demo has two types of motion: spinning motion (which is luminance-defined) and dropping motion (which is contrast-defined). Central vision processes are capable of keeping these types of motion separate from each other. Peripheral vision seems to lack these processes, and that is one reason why perception in peripheral vision can seem so strange.