Eye and head movements together

Figure 5.21: The head and eyes rotate together to fixate on new or moving targets. (Figure from MSC/Circ.982 20 December 2000.)

Although this section has focused on eye movement, it is important to understand that most of the time the eyes and head are moving together. Figure 5.21 shows the angular range for yaw rotations of the head and eyes. Although eye yaw is symmetric by allowing $35^\circ$ to the left or right, pitching of the eyes is not. Human eyes can pitch $20^\circ$ upward and $25^\circ$ downward, which suggests that it might be optimal to center a VR display slightly below the pupils when the eyes are looking directly forward. In the case of VOR, eye rotation is controlled to counteract head motion. In the case of smooth pursuit, the head and eyes may move together to keep a moving target in the preferred viewing area.