Clarification of transition conditions for eye movement while generating a trajectory using the upper limb

This paper describes the experimental analysis of eye movement during the generation of a trajectory by the human upper limb, carried out to elucidate the human mechanism for visual-information recognition. In the experiments preformed, subjects were asked to draw the trajectories of some kinds of images: a complete circle, semicircle, stippled circle. Reflective markers were attached to the subjects for motion capture, and a head-mounted eye-mark recorder was used to record eye movement. The results showed that the subjects adopted an eye-movement pattern called the subgoal travel method (fixating in the vicinity of the fingertip while drawing/tracing) for the complete circle. Subsequently, when the target trajectory was one of incomplete shapes, some subjects continued following the subgoal travel method by drawing the missing part of the target trajectory, while others followed two other eye-movement patterns. The first is called the center-point fixation method, in which subjects consider the center point as the most important point for generating the target-image trajectory, and therefore, fix their gaze at the center point throughout the experiment. The second is called the point-to-point travel method, in which the subjects' gazes shift between the center point of a displayed image and their fingertip. The results showed that the center-point fixation method provides greater visual information than the subgoal travel method. Further, the results confirmed that the eye-movement pattern, movement accuracy, and drawing speed are correlated. Additional experiments clarified the conditions for which different eye-movement patterns are suitable: the subgoal travel method is suitable for high-accuracy drawing; the center-point fixation method is suitable for higher-speed drawing. This study has revealed some interesting points underlying the eye-movement strategy used by humans for generating a trajectory.