Mona Lisa (IMAGE) Bielefeld University Caption For their study, the researchers used folding rulers for measurement. Study participants indicated the number they thought her gaze was directed at. Credit CITEC/ Bielefeld University Usage Restrictions The image may only be used with appropriate caption or credit. 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.