An object viewed directly (foveal vision) appears noticeably different from the same object viewed indirectly (peripheral vision). To investigate this aspect of how we see, our illusions accentuate the differences between foveal and peripheral perception. In one of these illusions, the “peripheral escalator,” zebra-like columns swing back and forth across the screen. Viewed foveally, the columns appear to move along a horizontal path; viewed peripherally (focus your gaze several inches above the screen), the columns appear to shift back and forth along a diagonal path. The results illustrate that peripheral vision is not just a blurry version of foveal vision.
Read more about the illusion and possible explanations