 Professor Margaret Livingstone of Harvard University has argued that the smile is mostly drawn in low spatial frequencies, and so can best be seen from a distance or with one's peripheral vision.Thus, for example, the smile appears more striking when looking at the portrait's eyes than when looking at the mouth itself.Christopher Tyler and Leonid Kontsevich of the Smith-Kettlewell Institute in San Francisco believe that the changing nature of the smile is caused by variable levels of random noise in the human visual system.