Contrast affects apparent speed 1. A light and a dark bar moving across the stripes are really in step but appear to move in alternation, like the two feet of a walking person.
Peripheral vision works well.
Contrast can affect apparent direction as well as apparent speed. As a dark square crosses a light horizontal stripe, its vertical motion is high in contrast and appears to speed up. Correspondingly, a light square appears to veer toward the horizontal, as in the magnified movie segment below.