# GazeRayHand: Combining Gaze Ray and Hand Interaction for Distant Object Manipulation
## 1 Introduction  
Manipulating objects at a distance is a fundamental interaction in virtual reality (VR) environments [1]. Like in the real world, walking to a distant object and manipulating it is realistic, but this requires two steps of interactions and is hence considered inefficient. Therefore, researchers have explored more efficient methods for distant object manipulation, such as extending the virtual arm to reach objects [2] or using controller-based raycasting [3, 4]. These methods allow users to reach and manipulate distant objects, but they still have significant challenges. Extended virtual arm techniques result in imprecise hand control due to scaling up the input, while raycasting methods reduce the intuitiveness and naturalness of interaction.  
Alternatively, gaze has been explored as a potential input modality for distant object manipulation, offering advantages such as rapid movement [5, 6], easy indication of a distant object [7], and reduced physical effort [8]. However, a simple gaze interaction has notable limitations: (1) the Midas touch problem [9], where simply looking at an object causes unintentional selection, and (2) limited interaction capabilities, as gaze primarily provides point information (i.e., indicating the point where the user is looking at).  
Recent studies have demonstrated potential solutions to these problems by combining eye gaze and hand inputs. For the Midas touch problem, many studies have adopted the principle of 'gaze indicates and hand confirms a selection' [10, 11, 12]. Combining hand input with gaze also addresses the issue of limited interaction by supporting diverse and sophisticated hand interactions [13, 14]. An interesting recent trend in using gaze input is exploiting a gaze ray, a line from the user's eye to the gaze point. [PERSON] et al. [15] and [PERSON] et al. [16] introduced Gaze Hand Alignment (GHA), a quick selection mechanism realized by placing a fingertip on the gaze ray. [PERSON] et al. [17] proposed Gaze Beam Guided interaction, which supports the translation of selected objects in the depth direction along the gaze ray.  
Numerous previous studies combining eye gaze and hand interactions showed effective distant object manipulation, but most previous methods control 6 degrees-of-freedom (DOF) manipulation simultaneously, which may reduce the level of accuracy [18]. Additionally, existing research has not thoroughly explored the potential of using the relative position between gaze and the hand for manipulation. Thus, this research aims to explore a method that leverages the relative position between the gaze ray and hand to support manipulation for each individual DOF.  
We explore two manipulation techniques: GazeRayHand and GazeRayHand2. GazeRayHand relies on hand movements relative to the gaze ray allowing for handling one or two DOFs separately for 3D object manipulation. GazeRayHand2 additionally employs gaze interaction for coarse object translation but still supports hand interaction. To evaluate these two techniques, we conducted a user study by comparing them with existing techniques that combine gaze and hand interactions: Gaze&Pinch [19] and modified Gaze Beam Guided [17]. To the best of our knowledge, this research is the first to introduce and evaluate an object manipulation method based on the relative position between a hand and a gaze ray.  
In summary, the contributions of this paper are as follows:  
* We utilize the relative position between the gaze ray and the hand for object manipulation.
* We propose two novel techniques that combine gaze ray and hand interactions.
* We evaluate our techniques by comparing them with other recent manipulation techniques that combine gaze and hand interactions.