# A Multi-Object Grasp Technique for Placement of Objects in Virtual Reality
## 3 Interaction Techniques
### Multi-Object Grasp  
Multi-object grasp combines the use of several buttons from the controller to enable the grasping and release of multiple objects (Figure 1). This technique permits the controlled release of objects, either by releasing one-by-one, or by releasing all of them simultaneously. In the real world, this activity can be represented as grasping several screws and releasing them one-by-one into each hole of a panel, or grasping the paper-clips on a desktop and releasing all of them inside a pencil-case. To develop the multi-object grasp technique, a preliminary study was conducted to analyse possible implementations for this new technique in a suitable and close-to-reality manner. The features that this technique needed are: grasp multiple objects that are directly reachable with the hand; keep control of when to release these objects; and make this experience as similar as possible to grasping in real life. We investigated how to map the movements performed by the fingers when grasping and moving multiple tokens in real life to the buttons of a controller, in this case an Oculus Quest controller. One approach was to use discrete gestures, for example, by performing a throwing action with the hand to release all tokens. However, discrete gestures were not as accurate, fast or comfortable as pressing the buttons. Another idea was to employ hand-tracking. However, this lacks haptic feedback, was more prone to occlusions during the tasks, forced the user to look at their hands while doing the tasks, and provided limited accuracy. The multi-object grasp technique was elicited through informal interviews. In order to obtain a natural set of interactions with the controllers for performing the actions (grab first, grab one, release all, release last), we gathered six people with backgrounds in computer science, electronics and medicine. Firstly, we asked them to perform the actions with real wooden tokens. Then we asked them how they would perform those actions with the game controller. Most participants agreed on the grab first action (pressing the ring trigger) and release all (releasing the trigger). For release one, some suggested a throwing gesture but others suggested pressing one of the top buttons. For grab one, there was no agreement between pressing the index trigger or doing it automatically when an object was touched while the grab first mode was held. We designed the multi-object grasp technique using the single-object grasp as a base and adding the support for multi-object on top. The base is that when the middle-trigger button is pressed, the objects intersecting with the hand are grasped. When this trigger is released, all the objects are released. Additionally, we need to grab extra objects or release a a single object while the middle-trigger button is pressed. For releasing a single object, we used the index trigger button, which was the most intuitive option for the users. For grasping an extra object, we used the button on top of the thumb. Figure 1: Multi-object grasp technique: (**a**) state transition diagram; (**b**) actions mapped into the controller’s buttons. We tested if extra objects should be automatically grasped when the users' hand came in contact with them or if it was better to actively press a button. Eight participants performed the study described in Section 4 with only the desktop and shelf scenarios and two conditions: using the index trigger in the controller to grab one object, or doing it automatically as the virtual hand touched an object while the grab mode was held. The task completion time (TCT) for the 'with-button' was M = 14.23 s SD = 5.58 s; for the 'no-button' condition M = 14.00 s SD = 3.84 s. A t-paired test reported a \(p\)-value of 0.43, so no significant difference was found between using the button to select each object or automatically attaching it to the hand.