Message Style and Speech Prosody in Voice Navigation: Effects on User Experience, Cognitive Load, and Emotions Across Road Complexities

Voice navigation systems play a critical role in supporting drivers, and their design can influence driving safety, cognitive load, and emotional responses. This study investigated how message style and speech prosody interact under varying road complexities to influence user experience, cognitive load, and emotion during driving. Using a driving simulator, young novice drivers completed tasks on simple and complex roads while experiencing two message styles (mandatory vs. guiding) and two speech prosodies (gentle-guiding vs. strong-direct). Subjective measures of user experience, cognitive load, and emotion were collected. Results show that gentle-guiding prosody consistently improves user experience, reduces cognitive load, and alleviated negative emotion. The optimal message style depends on road complexity: mandatory instructions are more effective on simple roads, while guiding instructions perform better on complex roads. We also propose design implications for future voice navigation systems in car based on our findings.