## 7 Validation with Users
### Procedure, Tasks and Experimental Design
Once a participant determines that the target height has been reached, the actual size of the model is recorded as well as the required time to perform the process. * **Task 4, mimicking real-life interaction metaphors for AR with mid-air haptics**: Both, this task and Task 5 are based on the Simon prototype. Again, the user is wearing the HoloLens which shows four colored buttons over the Ultrahaptics. Once the task starts, the user has two and a half minutes to complete as many sequences as possible. The participants are told to press the buttons, with no reference about how to do it. If the user hits the sequence, the system generates a new one with one more color. Otherwise, if the user fails, the system generates a new sequence with the same size but with different colors and the fail is saved. Besides that, the number of correct sequences is stored. * **Task 5, acceptance of AR with mid-air haptics with respect to a standard mobile baseline**: At this stage of the test, the participant is already familiar with the system. In this task, the user is asked to participate in a collaborative Simon game in two rounds. In the first round, the user will be interacting with the game through HoloLens and UHK while the facilitator will be using an AR iOS version of the game. The goal is the same as in Task 4, i.e., to hit as many correct sequences as possible within two and a half minutes. However, in this case, the user and the _facilitator_ must act in turns. First, the HoloLens client has to push a button and, then, the iOS client has to push the next one and so on. Both users receive the sequence at the same time, each one in their own device; at any time, it is possible to ask for help or instructions from the other user. Once this is finished, both users exchange the positions. Now, the _facilitator_ works with the HoloLens and the Ultrahaptics and the participant uses the iOS application. A new round begins then, just like the previous one. Figure 13 summarizes the workflows for the test and the questionnaires to be filled in at each stage. The experiment was designed as a within-subject one, with different factors depending on the task. For Task 1 and 2, factors were the availability of AR (two conditions: yes/no) and 3D figures (10 conditions). We have a total of 180 trials (10 figures \(\times\) 9 users \(\times\) 2 AR condition values (on/off)), with Task 1 including AR visualization and Task 2 relying only on haptics for guessing. As dependent variables, the execution time, interpretability values, and hits were measured. For Task 3, the factors are the 3D figure shape (5 conditions). Hence, a total of 45 trials have been gathered (9 users \(\times\) 5 figures, each one with the desired height associated). In this case, distance to target height and time have been the dependant variables. Regarding Task 4 (factor: haptic availability, 2 conditions, on/off) and Task 5 (factor: technology in use, two conditions mobile iOS vs. HoloLens + Ultrahaptics), the dependent variables gathered have been the number of correct sequences by the user as well as the number of fails together with user preference. Figure 12: Three participants trying to guess a figure from haptic feedback only in Task 2.