## 7 Evaluation
### Second User Study  
In the second user study, we wanted to evaluate the page content navigation techniques. In the first part of the online questionnaire, we asked for the age and gender of the participant. In the second part, participants could watch video-vignettes demonstrating the content navigation techniques, and order them by preference. The vignettes displayed a first person view of both the real and the virtual worlds and was narrated to further explain the techniques. In the third part of the questionnaire, we asked participants to (optionally) tell us why they ordered the techniques as they did, and to provide additional comments on each technique. In this study, we included additional page content navigation techniques beyond the two already described. In addition to the gesture slider and tangible slider, we included a touch technique where users could simply touch the bottom-left or bottom-right part of the page to slide left or right (implemented by detecting occluded markers on the bottom-left and bottom-right of the book). This served as a baseline comparison technique. Following the comments of the first study, we also included a voice technique were users could simply say \"next\" or \"back\". Results and Discussion  
We obtained a total of 50 responses, with participants' ages in the ranges [20; 29] to [50; 59] (44% of the participants were in the [20; 29] age range). Most participants (62%) were male. Results (Figure 9) indicate the participants have a higher preference for the gesture slider technique with 24 participants selecting it as the first option, and 15 selecting it as the second option. Many participants also preferred the touch technique, with 17 participants selecting it as the first option and 22 as the second option. The tangible slider obtained the worst results, with only four participants choosing it as the first option. Only a few participants (five) provided explanations as to why they ordered the techniques in a given way. Regarding the gesture slider, one participant said that \"for a book concept... [the gesture] seemed adequate\", while another justified the choice with the familiarity with the gesture. We hypothesise that participants associate the sliding gesture to e-book readers and hence feel it is familiar and appropriate for a virtual book. One participant that chose the touch technique as the first option, justified it with the importance of the physical touch. Although physically touching the book was not strictly necessary, our choice of words when describing the technique implied that touching was necessary, unlike in the gesture slider technique. This participant felt that touching would be an important aspect of the experience. We were disappointed that the tangible slider was the least preferred technique. To us, this was the technique that was more in line with the idea of a tangible interface and the one that provided the richest haptic experience. However, the results seem to indicate that it is not appropriate as a page content navigation technique in this context. Few participants provided comments specific to each interaction technique. Regarding the gesture slider, one participant suggested to use it as a way to vary the colour of some object in a more precise way. This comment seems to indicate that this participant did not fully understand how the gesture slider worked, which is comprehensible since participants only had access to a video-vignette. The gesture slider works as a discrete gesture, not as  
Figure 9: Page content navigation technique preference results from the second user study. a continuous one, which would make it difficult to use efficiently for a continuous task such as varying the colour of an object. However, this is a matter of implementation as it would be possible to create a continuous slider by calculating the distance of a marker on the slider to a fixed one. One participant suggested that the gesture slider might need some tactile element to indicate the interaction zone.