# Free-Hand Input and Interaction in Virtual Reality Using a Custom Force-Based Digital Thimble
## 2 Related Work
### Input Devices for Virtual Reality  
Most VR headsets or HMDs come with handheld controllers, which are typically composed of buttons, triggers, or thumbsticks and usually have motion-tracking capabilities. These features enable users to manipulate virtual objects or navigate through virtual spaces. The most common motion-tracking approach is raycasting, which allows users to control a ray pointing to a target with hand movements and use buttons or triggers to select and manipulate virtual objects [17]. There are also numerous approaches that enable the use of a controller as a virtual mouse [18]. Controllers, however, need to be held at all times, limiting the ability to perform other tasks with the hands. Performing gestures in mid-air with controllers often leads to errors, lacks precision, and can cause fatigue during extended use [6; 11; 16]. Additionally, controllers are challenging to use in confined spaces, such as while seated on a bus or train.  
Researchers have proposed various input solutions to address these challenges, including the use of smartphones [19; 20], digital pens or styli [21; 22; 23], and tangible objects [24; 25]. However, most of these solutions are aimed at and optimized for specific contexts or use cases. For example, smartphones are predominantly used to provide text entry solutions in VR, while digital pens and styli are primarily utilized to offer solutions for precise target selection. Consequently, these solutions outperform controllers in those specific scenarios.  
In recent years, there has been a growing interest in using traditional mice in VR [6; 11]. This interest is attributed to their longstanding use in computer systems, their higher accuracy and precision in target selection, and user comfort, as users can rest their hand on a flat surface [13; 21; 26]. In studies investigating the accuracy and precision of mice according to Fitts' law, mice have consistently outperformed modern controllers in terms of throughput by around 12% [21; 26]. Recent work has shown that a mouse is also effective in a 3D world despite being a 2D input device [11]. However, like controllers, mice require the use of the hand, thus limiting the hand's availability for other tasks. In addition, locating the mouse is not always straightforward, as users' sight is occluded by the HMD.  
Some researchers have proposed using existing or new wearable devices, such as smartwatches [27], digital gloves [28; 29], and finger wearables, for touch interactions [30]. However, these solutions either target specific use cases or come with a steep learning curve. They also tend to use bulky and heavy sensors, making them impractical in real-world scenarios. Wearable mice (Figure 1), commonly available on online shopping platforms, could serve as a bridge between traditional input methods and wearable technology, combining the accuracy and precision of a traditional mouse with the flexibility and portability of a wearable device. However, the effectiveness of these mice in VR has not yet been explored. The only related research identified that involved a wearable mouse examined its use to remotely control a telepresence robot [31], where it demonstrated a superior performance compared to a keyboard-based system.  
Bare-hand interactions using mid-air gestures are also commonly used in VR due to the availability of affordable hand-tracking technologies [32; 33]. However, the performance of these methods depends on the quality of the cameras used and can suffer due to occlusion or other environmental factors. This approach is also known to compromise comfort when used for prolonged periods [6; 7].