## 7 Evaluation
### First Study
It is not clear how bringing the book closer or further away to one's head could be generalised to other situations such as video playback, but it might something to explore in the future. Some respondents suggested combining automatic reproduction with manual, gesture-based commands to stop or to move the video forward or backwards. One respondent suggested an interesting shaking interaction to change the video, although it is not clear what was meant by \"change\": \"When the page opens the video starts. To stop the video you can touch the page. To change the video you can shake the page.\" The shaking interaction seems interesting because it relates to a physical action that we perform with a number of physical objects, including books. The meaning of that interaction, however, is not immediate. While we do sometimes shake physical books while holding the book's covers apart in order to make as small piece of paper that we know is somewhere inside the book fall down, this is not easily applicable to other situations. Still, it is a familiar gesture that might be interesting to explore. Some participants offered suggestions inspired in their experience with touch-based devices. For example, controlling the video manually by touching the page to start and stop and pressing specific areas of the page to fast-forward or backward. Interestingly, four respondents suggested the use of voice commands. Using voice commands with a tangible interface seems contradictory at first. However, for larger virtual books where the available physical pages are not enough to display all of the virtual pages some sort of controls would be required to access the additional virtual pages. In this situation, voice input might be an alternative to consider. Three respondents suggested the use of eye-tracking, perhaps as a way to select which video would play if several were available, in combination with other mechanisms. Regarding the interaction with hyperlinks (portals), comments were dispersed through several aspects. Three respondents suggested the use of voice commands as a way to activate the portals (\"We can interact with words perhaps? Saying ENTER IN...\"). Onerespondent suggested gaze-based interaction for entering a portal and another one suggested the use of specific areas in the physical page with a raised surface for haptic cue that would be pressed to enter the portal (\"The page would have zones to press that would correspond to linking options, the physical page could have reliefs that allow you to feel that there is where you should press.\"). One respondent suggested the use of hyperlinks as a way to open up information outside VR (\"Links could open a web browser close to you that shows the content.\"). Regarding the use of 3D content, respondents mentioned the importance of being able to inspect and manipulate the 3D model: \"I can look at a 3D model from any side, and I choose how to move the model\", \"Pop up models you can zoom in to, rotate or move out of the way to reveal what is behind them\". One respondent suggested the ability to take the 3D model off the page (\"Objects can be explored freely. I would like to touch the objects that are presented and be able to take them off the page\"). Although we have not prototyped this kind of interactions, they could be implemented in smartphone-based VR with the support of other tangibles to act as grabbers or through vision-based hand detection. Feedback Regarding Usability  
Participants identified a few problems in the depicted Tangible VR Book prototype. Some were related to layout or to the visual representation of the virtual elements in the book: some pages had a lot of unused space, the video was too small, the video did not look like a video but rather like a still image, the text was too small. Respondents also noted technical problems in the detection of the markers which made pages disappear momentarily. One respondent mentioned that the background (i.e., the 360 scenario) was distracting, however others mentioned the relevance of being able to look around.