Supplementary material for "Visual feedback for in-car voice assistants"

This study presents ambient visual feedback for automotive voice assistants to enhance driver interaction and safety through peripheral visual cues. A user interface prototype incorporating ambient colour feedback was evaluated through an online survey (N=151 from 28 countries) and a lab-based study (N=24, Belgium). Survey participants strongly preferred smartphone-integrated user interfaces, such as Android Auto and Apple CarPlay, over built-in manufacturer systems, indicating a desire for consistent digital ecosystems. In the lab, 18 participants favoured the ambient feedback over conventional or no visual feedback, citing improved visibility and assistance. Statistical analysis revealed that ambient feedback improved user visibility, position, and usefulness ratings. However, the need for auditory cues remained evident, confirming the importance of multimodal feedback. These findings suggest that ambient visual feedback is a promising direction for improving the usability of voice assistants and driver satisfaction while supporting safe in-vehicle interaction.