# Effect of Target Size, Location, and Input Method on Interaction in Immersive Virtual Reality
## 1 Introduction
In addition, a high level of interactivity in VR environment narrows the psychological distance between the user and the device [25; 26], and when experiencing a realistically implemented virtual environment, it can elicit a physiological response and emotional arousal similar to the response to a real-world's stimulus [27]. It is necessary to conduct more research to prepare interaction and interface design guidelines specific to immersive virtual reality environments. There are two types of immersive virtual reality input methods: (1) the method of additionally using a separate device and (2) the method using head tracking. PC-based virtual reality devices that connect to a computer equipped with high-performance graphics cards use these separate input devices. In case of using a separate device, a ray-casting remote controller, an eye-tracker, and a glove-type controller are used. The ray-casting is the method of showing the ray in the direction of pointing then selecting by pressing the button on the controller. It has the advantage that the movement of the controller is immediately reflected on the screen so that the operation is intuitive and easy, and tactile feedback can be obtained through an effect such as vibration. [PERSON] et al. [28] compared the task completion time of selecting an object in virtual reality when using the ray-casting with when using an eye-tracker. It was found that the task was faster with ray-casting than with eye-tracker. [PERSON] et al. [29] proposed three novel eye-tracking-based interaction methods and compared them with the eye-tracker method. The task performance was similar, but new techniques had a greater user experience. The interaction method using the eye-tracking technology is not dominant in the virtual reality market yet, but it is expected to be a natural interaction if the technology is implemented at a high level in the future. Finally, using a glove-type controller such as Leap motion [30] or Kinect is a method of wearing gloves with sensors and reaching out to an object or using gestures [31]. These allow greater freedom of hands and natural interaction [32], but it is not easy to obtain tactile feedback when input occurs [33; 34]. On the other hand, a smartphone-based virtual reality device uses the smartphone's touchscreen as the display and hardware of the virtual reality, and the role of the headset is to show the screen in three dimensions to the user through the lens attached to the VR headset. Among these smartphone-based VR devices, there are products that can use separate controllers, but low-cost smartphone-based VR headsets mainly use head tracking. This type of method can be divided into (1) the method of pressing the capacitive touch button on the virtual reality headset, and (2) the method of placing the cursor on the object and holding it for a certain time [35]. Smartphone-based VR is less expensive than a dedicated headset for virtual reality and does not require a high-end computer, so people who are new to virtual reality can easily access it. Since research conducted in the meantime is being conducted for PC-based VR devices, it is necessary to conduct research for smartphone-based VR devices. Therefore, the task performance and the level of virtual reality sickness were analyzed when performing input tasks using two main input methods--gaze selection and manual selection--mentioned above in smartphone-based virtual reality. In this study, participants selected targets not only within a viewing angle but also slightly away from the viewing angle, and task performance was analyzed by setting and quantitatively measuring variables related to task time and accuracy. In addition to the input method, how the user experience is affected by differences in interface elements such as the size and location of the buttons was compared. The purpose of this study is to investigate the size and position of the target (i.e., interface elements) and the effect of the input method (i.e., interaction elements) on task performance and VR sickness.