ABSTRACT
Visual demands on ocular torsion are different from those placed on horizontal and vertical eye movements. Retinal slip induced by image movement around the line of sight is greatest in the periphery of the visual field, and zero on the line of sight. A review of investigation shows that these decreased visual demands do in fact influence the control of torsional eye movements. In humans, the torsional responses to velocity steps in roll are considerably less than compensatory, with typical gains of 0.5–0.7. Gaze-dependent behavior of horizontal and vertical response magnitude during head roll has also been demonstrated, but not quantified or compared to torsional response magnitude. Horizontal and vertical responses during head roll, which are important for clear and stable vision, are more robust than the torsional responses typically thought of as the primary response to head roll.
