Eyes reveal our sexual orientation, scientists are convinced. A Cornell University study found that viewing erotic images and feeling arousal causes the pupils to unconsciously dilate. In this way, sexual orientation can be easily recognized. This is the first large-scale experiment to establish that the eyes can betray erotic thoughts, explains psychologist Rich Savin-Williams from the research team. If a man is heterosexual, his eyes widen when he observes a woman. And vice versa, for homosexuals, this happens when looking like a man, the scientists explain. The pupils dilate in response to any excitement or interesting stimulus, which is a sign that the autonomic nervous system is excited. It controls involuntary actions, such as heart rate and breathing. 325 men and women, heterosexual, homosexual and bisexual, participated in the experiment. They each watched a video of a man masturbating, a woman masturbating, and neutral landscape scenes. Using a camera, the scientists captured even the smallest changes in the size of the volunteers’ pupils. According to the results, heterosexual men respond to images of female representatives, homosexual men to male images, and bisexual men to both. NEWS_MORE_BOX Women’s reactions, however, turn out to be more complex, explains Rich Savin-Williams. While those who feel attracted to other women respond to pictures of the same sex, however, the pupils of heterosexual women dilate equally when seeing images of both sexes. This does not mean that all heterosexual women are bisexual, their subjective arousal does not necessarily match their bodily arousal, the research team explained. The method can be used to conduct cross-cultural studies of sexuality, as well as help people who feel confused in discovering their true sexual orientation, psychologist Savin-Williams believes. The results are reported in the journal Live Science.