Voiceless Can Speak With Their Eyes: Invention Measures Pupil Dilation To Allow Paralyzed To Communicate

on August 05 2013 12:20 PM
Watching for pupil dilation holds the key to communicating with paralyzed patients. Wikimedia Commons/Petr Novak

There’s new hope for people with disabilities or injuries that leave them frozen in place and unable to communicate. A group of scientists has come up with a way for a paralyzed person to answer simple “yes” or “no” questions without lifting a finger – a system that measures the changing size of the eye’s pupil to track mental responses.

The pupils of your eyes dilate and contract in response to emotional arousal, but the size can also be linked to other mental functions, like decision-making. The communication system developed by scientists at Philipps-University Marburg in Germany and their colleagues, and described on Monday in the journal Current Biology, harnesses the link between pupil dilation and mental effort.

"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," senior author Wolfgang Einhauser said in a statement.

In the setup, a camera connected to a laptop is trained on a patient’s eye. An assistant asks the patient a question with a yes or no answer – like “is your age 20?” After the question is asked, the answer “yes” or “no” is read by a computerized voice, while simultaneously a math problem appears on a computer screen.  After a few moments, the alternate answer is read out by the computer, and another math problem appears.

The patient is supposed to concentrate on solving the math problem that appears along with the correct answer to their question. The mental effort of solving the math problem translates into an automatic increase in pupil size, which is caught by the camera. You don’t even have to arrive at the right answer to the math problem – just trying is enough to trigger a pupillary response.

The researchers tried out the system on six healthy volunteers, each of whom ran through 30 trials. Then the team tried it out on seven patients with “locked-in syndrome,” who are aware and awake, but are paralyzed in virtually all of their muscles except for their eyes. The patients in question had suffered strokes that affected their brainstems. The results weren’t perfect but were encouraging.

"We find it remarkable that the system worked almost perfectly in all healthy observers and then could be transferred directly from them to the patients, with no need for training or parameter adjustment," Einhauser said.

Communicating with patients by decoding the pupillary response is a less invasive, more inexpensive alternative to current options such as electroencephalogram, or EEG, a test that measures brain waves. There are still some technical kinks to be worked out, but Einhauser and his team think they can keep improving the model. The systems may also be a helpful tool to determine if an unresponsive person is actually unconscious or just “locked-in.”

“For patients with altered state of consciousness -- those who are in a coma or other unresponsive state -- any communication is a big step forward,” Einhauser said.

SOURCE: Stoll et al. “Pupil responses allow communication in locked-in syndrome patients.” Current Biology published online 5 August 2013.