Giving fully conscious but paralysed people hard sums to do might seem like adding insult to injury. But because such brain teasers make the pupils of the eyes involuntarily dilate, it's providing a simple way for doctors to converse with people who are "locked-in"."It's been known since the 1960s that the pupil dilates with mental effort," says Wolfgang Einhäuser of the Philipps University of Marburg, Germany, and coordinator of the team that has developed and tested a communication system based on the phenomenon. "All you need is a laptop and a camera," he says.The laptop displays a difficult sum, such as 45 x 34. A patient is told to attempt to solve the sum only when the answer to a question is "yes". If the answer is "no" the patient should ignore the mathematical problem.
The camera is trained on the person's eyes to detect widening of the pupil. Tracking whether the dilation occurs allows doctors to discern the answer to a question.