# The Effects of Augmented Reality Interaction Techniques on Egocentric Distance Estimation Accuracy
## 1 Introduction
### Related Work  
As user interactions with virtual objects become more popular, it is crucial to determine an appropriate interaction technique and to design effective interactions with the 3D target in VEs. To design an effective and efficient user interface, it is also essential to understand the factors affecting the users' performance. Moreover, the design of the interface also needs to encompass an understanding of human behaviors--particularly when people are interacting in 3D space. Researchers have explored another 3D space input technique [18; 19; 20] as an alternative to traditional 2D input devices (e.g., mouse, trackball, etc.) and touch screens [21]. Generally, the technique utilizes 3D target pointing hand movement as an input function for various devices that require free-hand or touchless computer interaction. The question is whether such hand pointing interactions have the same performance as traditional 2D input devices. Several studies have successfully investigated user performance in human-computer tasks in 2D environments [22; 23] by utilizing direct-touch screens, as well as in 3D environments [17; 24; 25]. These are considered to be the same type of indirect interactions used in the present study. Nevertheless, to the best of our knowledge, comparative studies on how users interact with virtual targets considered direct and indirect interactions in our study are limited in number. Although previous studies have examined the performance of target acquisition in VE, the two techniques were considered separately (see Table 1 for an overview of studies on interaction techniques). This study, therefore, investigated the effects of direct interaction and indirect interaction techniques on the accuracy of egocentric distance estimation in a VE. We simultaneously employed direct pointing and a virtual cursor controlled by a gamepad for interactions in direct and indirect interactions. Another important factor in a VE is space and the perception of it. In addition, spatial information such as distance and size are fundamentally crucial in both the real world and VEs; furthermore, its information should be provided accurately [26]. However, biased perception of distance in VEs often causes users to over- or underestimate. The space in VEs can be divided into two measured distances: egocentric and exocentric distance. Egocentric distance is a distance between an observer and the object; usually, the observer estimates a depth toward the object. Exocentric distance is a distance between two objects. Cutting [27] defined a metric of depth from observer to target into peripersonal space, a distance extending a little beyond the arm's reach (about a radius of one meter) and extrapersonal space, which is all space beyond 1 m. Distance underestimation has been reported in the majority of studies of VEs [28; 29; 30; 31]. A systematic review of previous studies by [PERSON] and [PERSON] [32] found that the accuracy of distance in VEs was only about 80%, as compared to about 94% in the real world. Distance estimation in VEs can also suffer from worse inaccuracy, sometimes by as much as 50% of the intended distance [33]. Another study of egocentric distance perception in an IVE system by [PERSON] et al. [34] showed that distance accuracy was degraded by 45% (underestimated true distance within the range of 5 to 15 m). The study hypothesized that the inaccuracies and cue conflicts involving stereo viewing conditions in HMDs resulted in inaccurate absolute scaling of the virtual world. However, the results indicated that compressed egocentric distance judgment was not caused by the unnatural stereo viewing conditions commonly found in IVE systems. The study suggested further investigation of other factors as a source of the compression; e.g., the ergonomics of wearing the VR headset or sense of presence. Regarding the inaccuracy of distance judgment, previous research provides a variety of possible causes. An extensive review by [PERSON] et al.