Imagine That You Are at Niagara Falls, Staring at the Falling

Imagine that you are at Niagara Falls, staring at the falling water for a few minutes. When you look away from the water at the crowd of people, the people seem to be floating upward. What phenomenon have you just experienced?

A) Akinetopsia
B) Tau
C) Focus of expansion
D) Vergence eye movements
E) Motion aftereffect