## 4 Study Cases
### Case Study 1: Application for Teaching the Mexican Currency to Blind People  
Blind people face a number of visual challenges every day, from reading the label on a frozen dinner, to figuring out if they are at the right bus stop, to even identifying if they are paying with the right coin [49]. For this reason, when making different forms of coins and banknotes, it is important to take into account the fact that there are people who are visually impaired, but still need to understand the different values of the banknotes that exist [50]. Considering the importance of knowledge of currencies, the first case study proposes an application to teach currencies called \"Learning with Pesos\", whose objective is to teach the Mexican currency using tangible interfaces, gamification mechanics and the UDL. We decided to use tangible interfaces with the objective of taking advantage of the main means of interaction of blind people, their hands. In addition, through TUI, innovative educational and cognitive interventions can be maintained to listen and stimulate the narratives of visually impaired people [23]. Additionally, there are multiple projects which demonstrate favorable results in improving the learning of blind people with concepts of shadows, programming, music and Braille, among others [51; 52; 53; 54]. The application is composed of two main sections (see Figure 5a); the first section has the objective of showing descriptive information about the different coins/bills of the Mexican currency. for this, the user places an object with a coin attached to it on the tangible interface, then the application recognizes it and provides information through audio about its physical characteristics and the amount it represents, so that the blind person can identify it more easily (see Figure 5b). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case Study** & **TUI** & **ER** & **Challenges** & **Missions** & **Levels** & **Rewards** \\ \hline “Learning & \(\star\) & & \(\star\) & \(\star\) & \(\star\) & \(\star\) \\ with Pesos” & & & & & & \\ “Street & & \(\star\) & \(\star\) & \(\star\) & & \(\star\) \\ Simulator” & & & & & & \\ \hline \hline \end{tabular} \(\star\)
[FOOTNOTE:\(\star\)]  
Refers to elements available in the applications.[ENDFOOTNOTE]  
\end{table} 
Table 1: Characteristics in common in both case studies. Figure 5: (**a**) Main interface of “Learning with Pesos” application. (**b**) Descriptive cards section showing information about a 50c coin. The second section consists of a series of mathematical problems (addition and subtraction) that allude to possible events that the blind person could face in the real world, with the aim of improving their fluency in identifying Mexican currencies. In these sections it is possible to unlock different achievements by answering correctly and using different tangible objects. Figure 6a shows how the 2-peso badge is obtained after correctly answering an exercise, and Figure 6b shows the rewards interface where the achievements and their description are displayed; in the case of blind people these achievements are described through audio. To select mechanics and dynamics, we followed the gamification techniques selection process shown in Section 2, as described below. * What are user characteristics? Users for whom this application is intended have visual problems, such as total blindness or partial loss of sight, their sense of touch and hearing being their main means of interaction. * Which gamification dynamics and mechanics are the most suitable for the user according to their characteristics? Based on research that has previously used gamification techniques with blind children, the most appropriate dynamics are levels, challenges and missions, while the use of rewards as mechanics is considered appropriate [4, 55-57]. * How can we adapt these techniques according to user characteristics?