# Impact of Latency on QoE, Performance, and Collaboration in Interactive Multi-User Virtual Reality
## 3 Materials and Methods
### Experimental Methodology
#### 3.2.1 Use Case Description  
A collaborative two-user VR task is designed to be used as a proof-of-concept for the presented system. It consists of collaboratively baking a pizza together in a virtual kitchen. Figure 2 shows the kitchen layout. The tables are arranged in an \"H\" shape to divide the users. All the necessary ingredients are placed on the tables, which are positioned such that both users must pass ingredients to each other to complete the task. This requires close collaboration between the two users. Moreover, the virtual kitchen is equipped with an oven that is easily accessible to one of the users to bake the pizza. Since creating a pizza is a step-by-step process, a blackboard is attached to a wall in the virtual environment to inform the participants of what task to perform next. The cooking process is shown as a diagram in Figure 3 and consists of the steps listed below. Note that the virtual environment is constructed in such a way that neither of the users can access all the necessary utensils on their own, such that hand-over of objects is a key requirement for successful completion of the task.  
1. Add water and flour to a bowl. To this end, both water and flour should be handed over from User A to User B.
2. User B kneads the mixture until a ball of dough appears.
3. User B places the ball of dough on the shown indicator.
4. User A picks up the rolling pin and passes it over. User B holds it with two hands and spreads out the dough.
5. User B passes the spoon to User A. Afterwards, User A dips the spoon in the bowl filled with tomato sauce.
6. User A spreads the tomato sauce on the pizza. Once the spoon is empty, it should be refilled by dipping it in the bowl once again. User A keeps on adding tomato sauce until the pizza is fully covered.
7. User B uses the knife to cut four pieces of the sausage and four pieces of the bell pepper on the chopping board. To enable this, User A passes both the sausage and the pepper to User B.
8. User B places the four pieces of each topping on the pizza.
9. User B opens the oven by pressing the button.
10. User A passes the pizza shovel to User B. User B uses it to pick up the pizza and place it in the oven.
11. User B closes the oven.  
12. Once the pizza is baked, User B opens the oven.
13. User B removes the pizza from the oven with the pizza shovel and passes it to User A. User A places it on the plate.  
Note that the use case was chosen to include an element of gamification and a certain level of joy in order to avoid any bias due to user boredom after multiple playthroughs. As cooking games are widely regarded as enjoyable (e.g., \"Overcooked!\" ([[https://en.wikipedia.org/wiki/Overcooked](https://en.wikipedia.org/wiki/Overcooked)]([https://en.wikipedia.org/wiki/Overcooked](https://en.wikipedia.org/wiki/Overcooked)), accessed on 5 March 2024)), we believe this requirement is fulfilled. In addition, it is important to include an element of collaboration, as was discussed in Section 2.3. To this end, the use case has been designed such that the three main task types in collaborative VR, following the taxonomy of [PERSON] et al. (2017), are present. These include deliberation (conversations between peers, normally oriented to achieve a common goal), exploration (exploration of the environment and identification of objects following indications), and manipulation (interaction with system elements and manipulation of physical objects). Deliberation is intrinsically present as the use case cannot be completed successfully without appropriate communication between collaborators. Exploration is required to identify and find the correct objects (flour, water, bowl...) in the virtual environment. Manipulation, finally, is present as specific actions need to be performed on objects, including passing them between collaborators, to successfully complete the aforementioned tasks.