Paralyzed patients communicate by controlling their pupils

A team of brain scientists has demonstrated that some people with locked-in syndrome are able to answer yes-or-no questions by widening their pupils.

Usually pupils aren't under people's conscious control—that's the part of the eye that tightens in bright light, for example—but learning that control doesn't take any training, the researchers say. For the patients for whom the method works, a computer-and-camera setup was able to pick up their intended answer 67 to 84 percent of the time

The team originally found a 1964 study that showed that people's eyes dilate when they're doing difficult mental arithmetic. That eventually led the team to devise a computer setup that asks patients a question, and then shows them two possible answers in succession. Each answer is accompanied by a mental arithmetic problem. Researchers told the patients they only needed to work on the problem for the answer they wished to choose.

Just working on the problem is enough to dilate the eyes. The patient doesn't have to get the problem right, or even get all the way through the problem.

From  www.popsci.com/science/article/2013-08/paralyzed-patients-communicate-controlling-their-pupils