中央部に手をかざすとスピードアップ、周辺部に手をかざすとスローダウンしているように見える、とのこと。
When you cover up the centre of the image with your hand the dots will appear to speed up. Cover up the edges and they slow down.
http://www.ideaxidea.com/archives/2011/09/speed_illusion.html
http://richardwiseman.wordpress.com/2011/09/08/most-amazing-illusion-ever/