# Arm Posture Changes and Influences on Hand Controller Interaction Evaluation in Virtual Reality
## 6 Discussion
We named this contrastive performance of two hands the 'hand-use choice effect' which was rarely investigated in earlier research. Based on the hand-operational height effect and the hand-use choice effect, we suggest applying a hand-tracking technique in VR applications and identifying the operating hand in real time and, based on this, organizing the interactive space and the user-interface layout in the VR environment. Third, this study introduced a new evaluation metric--hand-operational persistence or task duration--to evaluate the hand-controller interaction more comprehensively. A higher persistence or a longer duration suggests that the interaction task is completed more coherently with fewer hand alternations. In this regard, the hand interaction task duration can be used as a metric for measuring overall task efficiency. In addition, the duration result was verified to be highly consistent with the user-perceived arm fatigue result. In this regard, the duration measurement can also be used as a metric in user-perceived comfort evaluation. The experiment was conducted in a virtual environment with an Oculus HMD for important reasons. First, the most fundamental purpose of this research was to investigate the hand-controller interaction performance and relevant influencing factors; however, there are multiple fields in which hand-controller interaction techniques can be applied, such as motion-sensing-based video games, VR and AR applications. Among these, VR is particularly a prevalent application in which hand-controller interaction is already widely integrated. Findings and inspirations gained from the current experiment can benefit many other similar applications. Second, the interactive space in a VR environment is far larger than those in other applications, and VR is the most representative application supporting motion-sensing interaction within a global space in which interactive objects can be placed at any position surrounding the body and the user performs different arm postures to adapt to the different objects. From this perspective, a VR environment is an appropriate setup for measuring the effect of arm posture and hand-operational position on hand-controller interaction. The participants recruited in the experiment were persons with basic knowledge of VR technology and hand-controller operation methods, or at least had experienced VR applications before. These participants were selected for specific reasons: according to our survey of the most representative empirical studies in the HCI domain in the last five years, the number of the participants ranged from six to thirty. Based on this, we suppose that a group size of thirty is appropriate and sufficient in this experiment. In addition, novice users need a long time to practice and become familiar with the VR environment before they can complete the interaction tasks successfully. However, experienced users can directly participate in the interaction tasks and generate a stable performance. Experimental results gained from experienced users can objectively reflect the reality of the target user group, thus this is a better choice. The experimenter surveyed three hundred volunteers through a questionnaire and found that sixty-nine of them qualified as participants. Most of these participants (>90.0%) were young users, aged from 21 to 36, indicating that users younger than 21 or older than 36 were uncommon users of VR technologies. Among these sixty-nine participants, there were eighteen females (26.2%), while the others were males, indicating that male users had a far larger percentage than female users of VR applications. Based on these, twenty-two males and eight females were selected as participants in the experiment. Nevertheless, it must be acknowledged that the gender factor and its potential effect have not been considered in this paper.