## 2 Backgrounds
### User-Based Testing with Users with Disabilities  
One of the most widely used methods that involves end users is usability testing, also called user-based testing, in which users perform real tasks with a prototype or real system [23], usually using one or more specific UIs. In the iterative user-centered design process, end-user participation is essential for applying techniques such as observation of users, performance-related measurements, questionnaires, interviews, and thinking aloud [28]. Especially when targeting users with disabilities, when it comes to user-based testing, it is essential to involve such users in the process to ensure that the product is usable and accessible to everyone. Usability assessment has been recognized as a critical success factor in developing usable interactive systems with increased productivity, reduced errors, reduced need for user training and user support, and improved acceptance by their users [29].  
User-based testing with users with disabilities is paramount for investigating interaction and other difficulties with the product and enhancing the accessibility of a product [30]. Moreover, the expertise of each user, the configuration of the system, and the assistive products [31] utilized by the user are just a few of the variables that can determine whether the user manages to overcome a potential barrier or not [19]. Users can also be asked to explore the product freely while their behaviors are observed and recorded to identify design flaws that cause user errors or difficulties [18]. During the session, a researcher or more researchers observe the participant's behavior and listen for feedback, enabling different variables to be measured (e.g., task completion time, the accuracy of execution, navigation behavior, etc.). Based on the qualitative and quantitative data analysis, the product's usability can be improved. The participatory assessment methods with real end users who employ a UI as they work through task scenarios and give feedback provide better insight into the underlying causes of system usability problems users encounter [29].  
When user-based testing aims to assess the solution's performance in terms of the speed of performing tasks or errors when using the solution, it does not matter which users we include. Existing research has shown that performance of users with disabilities while testing a product can be very close to the performance of users without disabilities [26; 32; 33]. However, when analyzing and comparing the benefits of products for users with disabilities, the results between users with disabilities and users without disabilities can differ significantly. The difference could be attributed to the greater utilization of new technology's advantages to people with disabilities, while those without disabilities take less advantage of the benefits or do not even need them as much. For example, the study by [PERSON] et al. demonstrated that older adults who are blind or have a visual disability and experience difficulties in navigating could significantly benefit from a navigation system, and evaluating older participants with a visual disability is important, as the majority of vision loss is related to age [32].