Examining the Fine Motor Control Ability of Linear Hand Movement in Virtual Reality

Linear hand movement in mid-air is one of the most fundamental interactions in virtual reality (e.g., when dragging/scaling/manipulating objects and drawing shapes). However, the lack of tactile feedback makes it difficult to precisely control the direction and amplitude of hand movement. In this paper, we conducted three user studies to progressively examine users' ability of fine motor control in 3D linear hand movement tasks. In Study 1, we examined participants' behavioural patterns when drawing straight lines in various directions and lengths, using both the hand and the controller. Results showed that the exhibited stroke length tended to be longer than perceived, regardless of the interaction tool. While displaying the trajectory could help reduce directional and length errors. In Study 2, we further tested the effect of different visual references and found that, compared with an empty room or cluttered scenarios, providing only a virtual table yielded higher input precision and user preference. In Study 3, we repeated Study 2 in real dragging and scaling tasks and verified the generalizability of the findings in terms of input error. Our core finding is that the user's hand moves significantly longer than the task length due to the underestimation of stroke length, yet the error of the Z-axis movement is smaller than that of the X-axis and the Y-axis, and a simple virtual desktop can effectively reduce errors.