The emergence of new immersive AR/VR headsets recently resulted in major improvements in hand-gesturebased user interfaces. Devices such as MS HoloLens II and Oculus Quest II support hand-gestures. Although using hand-gestures increases the sense of presence and ease of natural interactions, it has been shown that hand-gestures require extensive physical activity. Furthermore, it has been shown that the error rate in hierarchical menu selection is much higher when using hand-gestures than when using a desktop environment or the controllers. Therefore, assessing the difficulty of a hierarchical menu design when using hand-gestures and gaze for menu selection will enable UI designers to develop more effective user interfaces. In this work, we provide a validated index for estimating the hierarchical menu selection error using hand-gesture and head-gaze as input modalities. The index is informed by cognitive WAIS data gathered from participants, which measures subjective cognitive performance. The proposed index is the result of a user study that includes hundreds of hierarchical menu selections using MS HoloLens, and is validated against the data of a group of different participants. The results demonstrate that the index can successfully capture the trend of the users’ errors in selecting the hierarchical menu items in immersive environments.
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