## 2 Related Work  
### Participatory Elicitation Studies  
An elicitation method involves potential users in the process of designing any new type of interface or interaction. This approach allows designers to explore the possibilities of finding gestures from the end-users' perspective, which are often are not in the initial gesture set designed by the designers. User-preferred gestures are easier to remember than expert-designed gestures [28]. To elicit gestures from the users, an interface designer shows a result of an action for each task, known as referents [29]. The designer then asks each participant to imagine and perform an action that would cause each referent to occur. These user proposed actions are known as symbols [29]. The designer compares all of the symbols for a given referent from each participant and groups them based on their similarity. [PERSON] et al. [29] introduced a method to understand the agreement and other factors associated with user-elicited gestures. Their method has been widely used in other elicitation studies (e.g., [30; 31; 32]). Most recently, [PERSON] and [PERSON] [33] have redefined the agreement measurement to understand the data more precisely. This refined agreement formula and approach is applied in the analysis of our results.  
In terms of user-elicited gestures for augmented reality, [PERSON] et al. [34] presented a study of user-defined hand gestures for head-mounted AR displays. Their participants elicited gestures using both hands. By contrast, HAR devices are not head-worn and are often operated using only one hand on the touchscreen. Thus, interface metaphors of HMD AR are not suitable for HAR displays. In terms of interactions based on single hand thumb-to-fingers, [PERSON] et al. [35] presented a study of user-elicited single hand gestures using two or more fingers. They reported that both thumb and index fingers were highly involved in the interactions of their gesture set. Their study focused on the fingers and did not include the wrist, which can provide richer interaction possibilities (e.g., [36; 37]).  
The above studies do not use devices to elicit user-designed gestures. This approach enables users to propose any gestures regardless of their feasibility of implementation and the affordance of a device. Similarly, with their approach, the method of grouping the elicited gestures that look similar significantly influences the magnitude of user agreement rates [38] as this process is often dependent on the researcher's goals for the specific domain for which gestures were elicited. Therefore, by following their method, interface designers are unable to recommend a suitable sensing technology to recognize their user-elicited gestures. To address these issues, most recently, [PERSON] et al. [39] co-designed a prototype with potential end-users and conducted an elicitation study for a fabric-based wearable prototype to devise a taxonomy of wrist and touch gestures. Their non-functional prototype allowed the users to physically feel the affordance of the interface to perform their preferred gestures that are implementable in the functional version of the device. We adopted and extended their approach to elicit both wrist and thumb-to-index touch gestures to perform interactions with HAR applications.