# GazeRayHand: Combining Gaze Ray and Hand Interaction for Distant Object Manipulation
## 6 Discussion  
In this study, we evaluated the two proposed methods for object manipulation, GRH and GRH2, that exploited the relative position between the gaze ray and hand. In our user study, we compared them to two previous methods, GP and GB, and found four main results: (1) the GRH and GRH2 techniques helped participants reduce the total distance of object translation compared to GP and GB, (2) the gaze ray in the GRH and GRH2 techniques was used as a reference line so it was easy and intuitive to conceptually shape the direction of translation and rotation by the hand position relative to the reference, (3) the GP technique had an issue of requiring two hands while generally showing similar results with the GRH and GRH2 techniques, and (4) the GB technique was the worst because it required users to follow the three compulsory steps (horizontal/vertical translation, depth translation, and rotation) even when not all of them were necessary. Participants had a shorter object translation distance with the GRH and GRH2 techniques compared to the GP and GB techniques. With the GRH and GRH2 techniques, participants handled one or two DOFs translation individually. This individual handling reduced unnecessary translation while the participants had to perform some unnecessary translation with the GP technique that manipulated all three at once. Interestingly, this reduced manipulation distance did not lead to faster manipulation because at least two steps (1. horizontal/vertical translation and 2. depth translation) were required to completetranslation in 3D while 3-DOF translation was performed with one step by the GP technique (**H1** was not supported). However, we observed that although GRH was slower than GP during the coarse manipulation phase, it tended to be more efficient in the fine-grained manipulation phase. This suggests that GRH may offer advantages in tasks requiring fine control. The GRH and GRH2 techniques were easy and intuitive because they employed the hand position relative to the gaze ray to determine the direction and speed of translation and rotation. The gaze ray worked as a reference line and mapped the left/right, up/down, and forward/backward hand motion for moving or rotating an object in these directions. This simple design offered a high level of affordance due to its ease of memorization and quick learning. Additionally, based on perceived effort (i.e., arm fatigue and task load) and total hand translation, GRH and GRH2 consistently resulted in lower fatigue and required fewer hand movements, particularly compared to GB. This suggests that GRH and GRH2 are more suitable for prolonged use in VR environments and may help mitigate the gorilla arm effect [29] (**H2** partially supported). Interestingly, the benefits described in the previous two paragraphs were less obvious with the GRH2 technique compared to the GRH technique. The main difference between them was whether they supported gaze-based translation or not, while the hand-based translation and rotation were consistently supported. This gaze based translation was fast, so some participants preferred it, but it had an issue of Midas touch which resulted in translating an object unintentionally. The GP technique showed similar results with the GRH and GRH2 techniques in overall objective and subjective measurements (including total rotation degree, total head translation and rotation, arm fatigue, task load, usability, and pragmatic and hedonic qualities). However, the GP technique had a notable limitation: requiring two-handed manipulation for rotation. Since the experimental task did not include other tasks such as holding another object or shooting with a hand during manipulation, the issue was not clearly revealed. We note that the issue could be more prominent with the tasks requiring additional hand operation. The GB technique was the worst among the four techniques. The GB technique included three compulsory steps for three types of manipulation: horizontal/vertical translation, depth translation, and rotation.