Figure 3.

Sequential structure of rotations in the kinematic model. In the first two panels, blue, red, and green curves, respectively depict gaze, eye-in-head and head trajectories. (A) Typical 1-D behavioral diagram from the experiments on natural head-unrestrained gaze-shift (Guitton et al., 1990; Freedman and Sparks, 1997). This observed pattern has inspired the sequence of events devised in the static kinematic model. (B) Succession of movements in the kinematic model. Head remains fixed while the eye is moving in the head. Then, head rotates, moving eye with itself such that eye-in-head position remains unchanged; this rotation foveates the target. Then, head rotates to its definite position, while eye rotates in head to compensate for head movement and keep the target foveated. (C) Having solved the equations of the model based on our physiologically inspired assumptions and constraints, we find that the saccadic eye movement has its independent axis and can be implemented in any duration of time which ends before onset of VOR (red double-headed arrows). Onset of head movement is arbitrary but its two parts are implemented continuously after each other (green double-headed arrows). Eye rotation during VOR is implemented right at the time when the second part of head movement is happening (violet double-headed arrow).