Comparison of kinematic and visual servoing for fixation

This paper describes experiments in estimation and control of the fixation point with a 10 degree of freedom head-neck-body system. A system has been constructed which uses standard kinematic techniques to estimate the fixation point. Two approaches have been investigated to control the fixation point: 3D kinematic estimation and 2D visual servoing. Kinematics is shown to be efficient provided that there is a sufficiently precise model of the kinematic chain. In particular, large errors in the kinematic model can cause the system to oscillate. In contrast, visual servoing is extremely robust with respect to errors in the kinematic model, but require a much larger (factor of 10) number of cycles to converge. The two approaches are found to be complementary. Kinematics can be used to perform a ballistic saccade to the fixation point, while visual servoing serves to correct small errors with a “micro-saccade”. This approach mimics saccadic control found in the human visual system