I think she is mixing up: 1. Shading. 2. Motion parallax. When you move your head, objects in the foreground move more. 3. Microsaccades. If your eye points pe

I think she is mixing up: 1. Shading. 2. Motion parallax. When you move your head, objects in the foreground move more. 3. Microsaccades. If your eye points perfectly steady, your retina adapts to the constant stimulus and the image disappears. So your eye moves slightly, all the time.