# Shared eHMI: Bridging Human-Machine Understanding in Autonomous Wheelchair Navigation
## 2 Related Works  
### eHMI and Projection Interaction of Autonomous Vehicles  
External human-machine interaction (eHMI) arises as a solution for the vehicle to transmit information to potentially dangerous agents in the vicinity, representing a newly developing direction of autonomous driving [13]. eHMI encompasses the interaction design between autonomous vehicles (AVs), pedestrians, and other road users, primarily involving the communication of the vehicle's status, intentions, and interaction modalities with pedestrians [6]. As ADS technology advances, the clarity and comprehensibility of such interactions become pivotal for road safety. [PERSON] et al. conducted an experiment and reported that eHMI has a positive effect on other drivers' ability to infer the AV motion intentions [14]. In addition, the congruence of eHMI with vehicle kinematics has been shown to be crucial. [PERSON] et al. found that when eHMI signals matched vehicle movements, drivers experienced fewer crashes and passed more quickly than without eHMI [15]. [PERSON] et al. 's study demonstrated that any eHMI contributes to a more positive feeling towards AVs compared to the baseline condition without eHMI [16]. These indicate that eHMI facilitates effective communication, reducing the uncertainty in intention estimation and thereby preventing accidents. The design of eHMI could be multiform and multimodal. External interaction screens, matrix light, and projection interfaces are widely used in eHMI design due to their versatile interaction capabilities with diverse road users [17]. Among these, common visual communication modalities encompass emulation of human driver communication cues, textual interfaces, graphical interfaces, lighting interfaces, and projection interfaces [18; 19; 20; 21]. [PERSON] et al. evaluated the multimodal eHMI of AVs in virtual reality. Participants, as pedestrians, felt an increased sense of safety and showed a preference for the visual features of arrows [22], offering insights for future design. [PERSON] et al. explored the use of projection-based methods in virtual environments to facilitate interactions between AVs and pedestrians [23]. Additionally, on-market vehicles have experimented with headlight projections to convey information. These highlight the implementation of projection as a visual form of eHMI, suggesting further potential for exploration in this area. On lightweight vehicles such as wheelchairs and electric bicycles, eHMI in the form of on-ground projections is more reasonable. Utilizing on-ground projections, information can be directly exhibited on the roadway, offering explicit motion intentions or navigation paths. This approach of integrating interfaces with the environment through augmented reality offers communication that is intuitive and visibly clear, unaffected by the movement of vehicles [24; 21]. Notably, augmented reality technology and multimodal interfaces are now considered effective means for ensuring smooth and comfortable interactions [25; 26]. This provides insights for the exploration of more complex and engaging interfaces, especially through the method of on-ground projections. eHMI has more value in social attributes and interaction design. According to the research of [PERSON] et al. and [PERSON] et al [27; 28], eHMI in the form of on-ground projections, particularly those conveying functions of autonomous driving mechanisms like parking and alerting pedestrians, are predominantly accepted by the majority of individuals. The experiment by [PERSON] et al. [29] showed that this form of eHMI is safer, more helpful, and better at maintaining users' attention on the route. Interestingly, for wheelchairs with on-ground projection-based eHMIs, this system serves not only as an external interaction tool but also plays a pivotal role in the user-wheelchair interaction due to the visibility of the projection in public spaces.