Sad masked vs. unmasked faces (IMAGE) University of Southern California Caption The research found that expressions of sadness were the most difficult to identify for all age groups. Credit Composite/Courtesy of Yael Waizman Usage Restrictions Credit must be given to creator. License Original 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.