Illusion teaches people to write with their eyes

Science : Reverse-phi motionâmdash;the illusion that an image that alternates between black and white is moving in the direction opposite its actual motionâmdash;has been used to teach people to control “smooth pursuit” eye tracking and could form the basis of a new means of communication. Smooth-pursuit tracking is not easy to maintain because human eyes normally move in a start-and-stop manner called “saccadic motion.” Because the background in reverse-phi illusions appears to flow, it can be used to train the eye to follow that flow. Jean Lorenceau, a cognitive neuroscientist at the Pierre and Marie Curie University in Paris who developed and tested the technique, also discovered that people who have learned to control their smooth-pursuit eye motion can then use that ability to “write” with their eyes by means of eye-tracking software. That ability could allow people who have been paralyzed by disease or injury to communicate much more easily than with the systems currently available.