# Arm Posture Changes and Influences on Hand Controller Interaction Evaluation in Virtual Reality
## 1 Introduction  
Benefiting from a rapid development in motion-sensing and computer graphic (CG) technologies in recent years, VR has become an increasingly prevalent technology in sports and rehabilitation training [1], immersive entertainment [2] and education [3], and more other spatial simulation and exploration domains. For example, in geological research and educational practices, researchers used VR technology to recover and simulate geological heritages, which has proven to be an effective means for immersive visiting and learning by academics and the public [4, 5]. Especially when other cutting-edge technologies, such as natural language processing (NLP) and brain-computer interface (BCI), are integrated into VR, people have more opportunities to experience novel products and services, including, but not limited to, immersive storytelling, neuroimaging and psychotherapy [6, 7]. In various VR applications, users are immersed in a computer-simulated stereoscopic environment through head mounted displays (HMDs) such as Oculus Rift, HTC Vive and Meta, and acquire and manipulate virtual objects through a handheld controller or bare hand, as if in the real world. There are a variety of common interaction tasks in a VR environment, including spatial navigation, information retrieval, target moving and dragging. Among these, target acquisition, which consists of two steps, i.e., target pointing and target selection, is the most fundamental, but representative, interaction task [8, 9].  
Hand-motion sensing-based interaction, including bare hand interaction and a hand controller-based interaction, is largely limited by the biomechanical structure of the user's arm and its kinematic features [10; 11; 12]. The user performs different arm postures to acquire targets at diverse positions in mid-air, as illustrated in Figure 1. Earlier kinematic studies revealed that hand operation in some postures was perceived to be more comfortable than in other postures. In particular, a downward arm posture was generally more relaxed than an upraised arm posture, and a bent arm posture was generally more labor-saving than a stretched arm posture [13; 14]. However, how arm posture and hand-operational position affect hand interaction performance, e.g., accuracy of acquiring virtual objects and hand-operational persistence, were less investigated. Because of this, user interface layout design and interactive space organization in current VR applications are often arbitrary.  
To fill the knowledge gap and, more importantly, to develop guidelines or strategies for designing highly efficient and user-satisfying three-dimensional user interfaces (3 DUIs) in VR applications, we recruited thirty participants to complete a specifically designed target-acquisition experiment. In this experiment, targets in the VR scene floated at different positions, and the participants performed different arm postures to acquire these targets. Except for the arm posture, the user's handedness and hand choice were also identified and defined as independent variables in the experiment. We measured target acquisition accuracy and hand-operational persistence in different conditions of hand choice and arm posture and, based on these, concluded kinematic influences on the interaction results.  
The remainder of this paper is organized as follows: Section 2 presents an overview of related work. Section 3 states the research objectives and hypotheses development. Section 4 gives an introduction to the experimental method, including information about the participants, apparatus, experimental design, procedures and analytical methods. This is then followed by Section 5, which presents the experimental results and hypotheses verification. Based on the experimental results, Section 6 provides a discussion about the experimental findings and related implications. Finally, Section 7 concludes this research work.