## 5 Immersive Interface Testbed: An Evaluation Example
### Evaluation Procedure  
To analyze the effect of immersive and egocentric visual feedback, participants were asked to perform three hand-eye coordination tasks using two visual interfaces: traditional interface: fixed monitor, a single point of view with a wide view scene (\(Fix_{Display}+Fix_{Cam}\)) vs. the immersive interface: HMD and controllable point of view (\(Rift_{Display}+Mov_{Cam}\)). **Task 1**, touch: Users should press on several key blocks using a 1 m stick according to a random sequence defined by the computer (the time to accomplish the task was measured and block touch mistakes) (see Figure 3). **Task 2**, pick-and-place: Users should grab five blocks of different shapes using a manual gripper (80 cm long) and insert them into the respective hole of a wood box (the time to accomplish the task was measured; insertion difficulties due to spatial perception errors or handling were interpreted as delays) (see Figure 4 where blocks with different shapes like cylinders, cubes, and triangular prisms only enter in the right hole shape; time recording starts with the first block grab and ends with the last insertion). **Task 3**, path following: Users should follow a predefined 3D path with a metal loop at the tip of a stick (the time to accomplish the task was measured and the number of hits loop/wire recorded). This setup consists of one metallic pipe with curved and straight paths, where the user should move the metal loop along the pipe, avoiding electric contact between both (see Figure 5). Participants started randomly, either with Interface 1 or 2, to mitigate the effect of the learning factor. Task 2 and Task 3 were performed in a random order for the same reason. The evaluation consisted of analyzing a set of performance-related parameters, which were collected during the experiments, and the answers given to a short questionnaire after each trial. The collected parameters, the questionnaire, and their analysis are presented in the remainder of this section. The procedure can be summarized as:  
1. The participant is instructed about the task objectives and procedures. 2. Execute the trial (Tasks 1, 2, 3) with one of the two setups randomly selected. 3. Fill in the questionnaire about the user experience. 4. Repeat until four trials are complete. Figure 3: Task 1 setup used to compare performances. The user using a hand stick presses a sequence of key blocks defined by the computer at random. Interface view shows the next block to touch at the upper left corner of the display, after each correct touch. (**a**) Traditional interface vs. (**b**) immersive interface. The procedures of the control experiment consisted of a typical pick-and-place task using different media interfaces randomly following the repeated measures approach (within subjects); see Figure 6. Users were asked to perform the task using:  
- Direct vision (stereo binocular) and his/her bare hand (the baseline);  
- Direct vision (stereo binocular) and a manual gripper;  
- HMD indirect vision (mono biocular) and his/her bare hand;  
- HMD indirect vision (mono biocular) and a manual gripper;  
- Monitor indirect vision (mono biocular) and a manual gripper;  
In the _\"direct vision (stereo binocular)\"_ setup, users used direct visualization to grab the blocks and insert them into the respective holes of a wood box, either using their hand or a manual gripper (80 cm long). In the _\"HMD indirect vision (mono biocular)\"_ setup, users used an HMD with a monocular video camera fixed in front of it, creating a video see-through HMD. The users used their hand or a manual gripper to manipulate the blocks and could move their head freely (position and orientation). Because the camera and HMD display have different resolutions and FoVs, the 1:1 magnification was not suitable. To reflect the true size of the objects, the user adjusted the viewing image to half of the original size (looking either directly at the scene or through the \"video see-through HMD\").