## 5 Experiment Results and Discussion
### Discussion and Limitations  
Achieving specified goals effectively, efficiently and with satisfaction impacts not only the usability of a product but also its accessibility, especially when considering users with disabilities. While _usable accessibility_--an approach ensuring that a product is both technically and functionally accessible--is commonly discussed in the context of web design [77], we believe that it can be applied to serious games based on handheld AR. Similar to how the Web Content Accessibility Guidelines (WCAG) 2.0 [78] can be applied to non-web information and communication technologies [79], these guidelines can direct accessible interaction design in AR environments. In particular, our study aligns with the _Operable_ WCAG principle, which emphasizes that user interfaces should be easy to navigate and interact with for a wide range of users, including those with disabilities [78]. One of the WCAG guidelines related to the _Operable_ principle states that users should be able to operate functionalities through multiple input methods beyond just keyboard input [80]. For example, complex touch gestures, such as drag-and-drop and swiping, should have alternative methods of interaction to accommodate users who may struggle with these gestures. Applying this guideline to transformation tasks in handheld AR, we introduced indirect controls, i.e., buttons, as an alternative to touch gestures. This provides an accessible option for users who cannot perform certain gestures, either permanently (e.g., due to motor impairments) or situationally (e.g., due to different situational circumstances). Our user testing results indicate that most participants were satisfied with their assigned interaction mechanisms for interacting with the virtual object. Notably, most of the participants were assigned indirect controls, which proved beneficial for transformation tasks that were more challenging (i.e., rotation and scaling), as reflected in the results for interaction parameters such as completion time, skipped tasks and interaction satisfaction ratings (Section 5.2). These findings highlight the importance of offering multiple interaction mechanisms to accommodate diverse user needs. However, preferences for interaction mechanisms vary. Some users may find touch gestures more intuitive, while others prefer indirect controls depending on the context and task. Thus, it is also crucial to ensure that indirect controls do not interfere with AR content and can be removed when unnecessary. The ideal interaction experience should be adaptable. For example, users with motor impairments may require larger indirect controls \begin{table}
\begin{tabular}{c c c c c} \hline  & **W** & **z** & **_p_** & **r** \\ \hline Translation 2—Translation 1 & 978 & \(-\)1.209 & 0.227 & - \\ \hline Scaling 2—Scaling 1 & 390 & \(-\)4.55 & \(<\)0.001 & \(-\)0.44 \\ \hline Rotation 2—Rotation 1 & 913.5 & \(-\)2.575 & 0.010 & \(-\)0.25 \\ \hline \end{tabular}
\end{table} 
Table 12: Wilcoxon signed-rank test results for comparison of interaction ratings in SG1 and SG2. to prevent unintended touches, while users with visual impairments may find on-screen buttons distracting or obstructive on small mobile screens. To enhance accessibility and user experience, AR systems should dynamically adjust interaction mechanisms based on user needs and context. By tracking relevant interaction parameters alongside contextual data, systems can recognize when specific mechanisms are needed (or unnecessary) and adjust accordingly. For example, a system could automatically remove visual buttons for users relying on audio cues or enlarge indirect controls for users with motor impairments. However, the best approach to adapt the solution to the user needs to be investigated more in terms of continuous adaptations while considering the risk of user dissatisfaction caused by sudden adjustments.