## 4 Discussion
### Study Limitations  
Using think aloud as a data collection tool, and the Nielsen number limits the number of participants by design [27]. With a larger sample size and improved statistical power the confidence intervals would be more likely to be valid, though they currently calculate negative.After conclusion of usability testing, a larger validation study could rectify this and decrease the possibility of a type two statistical error. Another potential limitation for the results of the study lies in the selection of non-disabled participants as the sample population. As this study aims to prove that an eye-tracking interface can be implemented to provide navigational control in game, it is important to ensure our sample population is capable of generalization [48]. The chosen population, individuals without disabilities from ages 18 to 65, was selected to ensure that there would be no confounding variables. Though many individuals with ALS, especially early in the course of the disease, may have the control of their extremities required for in-game selections this may provide an additional limitation. The feedback from the pilot mobility research study validated the steering control potential for this new hands-free control system. Commentary from patients and caregivers focused around the challenges learning the system reliably while driving in physical space. This was the driver for the stress-free gamified training system. The focus of the training software has been to refine the training software prior to working with ALS patients. Throughout the clinical research, the reminder was that every challenge the vulnerable patient group struggles with from design or implementation challenges has a significant time cost for the patient. This necessitates usability and efficacy benchmarking throughout the training platform to minimize such potential burdens. This study sought to prove that an eye-tracking interface was as effective as traditional in game navigation. Individuals living with disability provide insight unique to their own experiences that will benefit the usability design. The video game's design and implementation continue through an iterative process, with playtesting and evaluation being critical to the process. The results of this study suggest that a traditional mouse and keyboard and the eye-tracking interface are similar in usability. The results are not necessarily generalizable to the ALS patient population. Each cohort was composed of five individuals, as past research in usability has found that the majority of issues can be identified in this manner [27]. Though other sources argue that a larger number of individuals should be included to find usability errors [49], it should be noted that this is not the first time this game has been played through. The game was played through by the game creators as well as researchers prior to administration of the study. As such, past prototypes of the game were tested iteratively prior to admittance of users in the formal usability study. It should additionally be noted that because the designers of each level were comfortable with the interface, the game was not played through in its entirety, and therefore, prior build errors were not caught. This error is common in expert reviews that are interface specific rather than task specific [50]. Further iterations are likely to be made in subsequent studies with ALS patients, where _Limbitless Journey_ will be utilized as a training platform for the EMG-wheelchair interface. During initial testing, the eye-tracking cohort (Cohort 1) experienced software issues. These problems included freezing in the midst of gameplay and when selecting menu options during the calibration period. Buttons towards the edges of the screen were unable to be selected via the eye-tracking interface. Other software bugs included on-screen buttons being permanently selected regardless of the user's gaze.