Answers to Yes/No Questions Seen in Pupil Size: Study

People who are otherwise unable to communicate with others can answer yes or no questions with a simple system that measures changes in the size of their pupils, researchers say.

The system consists of a laptop and camera and takes advantage of naturally occurring changes in pupil size that occur when people do mental arithmetic. No specialized training is required, according to the study authors.

Along with helping "locked-in" people communicate, the system might also prove effective in assessing the mental state of people whose level of consciousness is unclear. Locked-in syndrome is a rare disorder in which voluntary muscles in all parts of the body -- except for those that control eye movement -- are paralyzed.

The researchers developed the system in experiments with healthy people and tested it on seven patients who had stroke-related brain damage and were unable to communicate. In many of those patients, their responses to yes or no questions could be determined based on pupil size alone, according to the study in the Aug. 5 issue of the journal Current Biology.

"It is remarkable that a physiological system as simple as the pupil has such a rich repertoire of responses that it can be used for a task as complex as communication," Wolfgang Einhauser, of Philipp University of Marburg in Germany, said in a journal news release.

He said further work is needed to improve the system's speed and accuracy, but added that these technical issues should be easy to solve. In its current form, the system could already make an important difference to people who need it most.

For patients in an unresponsive state, "any communication is a big step forward," Einhauser said.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about locked-in syndrome.