Iris-sclera configuration was a possible mechanism that contributed to people’s worse performance at discriminating facial targets situated on the central part the face. Since the cones can perform much better on perceiving details, people would move their irises to inspect a particular target. As the iris moved, people could notify the gaze direction from the asymmetric sclera. However, the horizontal length of an eye is longer than its vertical length. When people looked at right or left side, the iris moved by a larger extent than when it moved upwards or downwards. Due to the less obvious asymmetry, it was more difficult for people to distinguish upwards or downwards gaze. While comparing with hair and chin, the distance between eyes, nose
