Stress can improve performance for confident students but lower it for more anxious ones, a University of Chicago researcher says. Knowing how to deal with stress can make a big difference in performance, says Sian Beilock, an associate psychology professor and expert on poor performance by talented people. In a study published in the current issue of the journal Emotion, Beilock and colleagues examined poor performance in math and found cortisol, a hormone released in response to stress, can be linked to poor performance or success, depending on the state of mind of the student going into the test. The researchers tested 73 undergraduate students to determine their working memory -- the mental reserve used to process information and figure out solutions during a test -- and their level of math anxiety. For people with large working memories, typically the most talented, increasing cortisol could lead to better or worse performance, depending on whether they were already anxious about math, the study found. Among those who had no fear of math, increased cortisol during the test led to better performance while for those with higher math anxiety, it was linked to poor performance. "If a student interprets their physiological response as a sign they are about to fail, they will. And, when taking a math test, students anxious about math are likely to do this," Beilock said. "But the same physiological response can also be linked to success if a student's outlook is positive." Students, she said, can improve their performance by writing about anxieties before a test or thinking about a time when they have succeeded.