# GazeRayHand: Combining Gaze Ray and Hand Interaction for Distant Object Manipulation
## 2 Related Work
### Combining Gaze and Hand for Object Manipulation  
In daily life, humans naturally use their eyes to see a target object before selecting and manipulating it [30; 31]. The gaze interaction is fast [5; 6] and requires low effort [7; 8], while the hand interaction is intuitive and allows for precise adjustments [32]. Therefore, many researchers have adopted the combination of gaze and hand interactions and demonstrated its effectiveness [19; 33; 34; 32].  
For example, [PERSON] et al. [10] proposed the Gaze+Gesture technique in a desktop environment. In this technique, a user's gaze quickly sets the approximate initial position of a cursor, followed by fine adjustments using hand gestures. In their user study, the combination of gaze and gesture interaction outperformed gaze or gesture alone in terms of precision and time in a positioning-objects task using the cursor. Similarly, [PERSON] et al. [34] investigated a method for switching between direct and indirect hand manipulation based on the position of the gaze on a 2D touch display. If the hand input is within the gaze region, direct hand manipulation is applied to the target object. Conversely, if the hand input is outside the gaze region, indirect manipulation is activated for applying the hand input at the gaze position on the 2D touch display.  
Extending the concept to 3D VR environments, [PERSON] et al. [19] introduced the Gaze&Pinch technique, where a user selects a distant object by looking at it with a gaze and confirms the selection with pinching. After the selection, the user can translate the object by moving the hand until the pinch is released. This technique also supports rotation by a two-hand interaction. The technique rotates the selected object in the direction which the movement of the two hands represents.  
Some researchers have explored gaze manipulation after selecting an object [13; 14; 17]. [PERSON] et al. [13] introduced 3 DMagicGaze, which supports coarse translation based on gaze movement and fine hand manipulation. They established a circular region around the target object, and if the gaze point is within this region, hand manipulation is applied. Otherwise, if a user moves their gaze outside the region, the object is translated at the gaze direction. One significant limitation of this technique is depth translation by hand operation which is restricted by the arm's reach.  
[PERSON] et al. [17] proposed a method that extends gaze-based translation not only in the lateral or longitudinal directions but also in the depth direction. Their approach consists of three steps: selection, the first translation step in lateral and longitudinal direction, and then the second step for depth translation. Selection is confirmed by releasing a hand pinching when aligning a gaze ray with a target object. In the first translation step, the target object moves according to eye movements, and then fine translation is performed using the hand adjustment. When the first translation ends, the direction of the gaze ray is fixed, and moving the hand forward or backward makes the target object move forward or backward along the ray, respectively, for depth translation. While supporting translation in three dimensions, this method does not support object rotation.