In this paper we study the human eye movement and the head movement system as a simple mechanical control system. Most of the time, eye movements obey Listing's constraint, which states that the allowed orientations of the eye are obtained by rotating a fixed 'primary gaze direction' by a subclass of rotation matrices. These rotation matrices have their axes of rotation restricted to a fixed plane perpendicular to the primary gaze direction. Likewise, a spontaneous head movement satisfy Donder's constraint which is similar to the Listing's constraint except that the axes of rotation of the head away from a primary head position is restricted to a fixed surface, which is not necessarily a plane. When head is restrained to remain fixed, eye movement satisfies the Listing's constraint throughout its entire trajectory. On the other hand, when the head is allowed to move (satisfying the Donder's constraint), the eye satisfies the Listing's constraint ...
Bijoy K. Ghosh, Indika Wijayasinghe