Figure (IMAGE) U.S. Army Research Laboratory Caption Pupil size changes in response to math problems classified as easy (light shade) or hard (dark shade) and correct (green) or incorrect (red). Credit US Army image Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.