Performing E-mail Tasks While Driving: The Impact of Speech-Based Tasks on Visual Detection

Abstract

Drivers listened and responded to e-mail messages presented in a human voice and two types of synthetic speech (concatenative and formant) while driving a simulator. Their performance for visual event detection, vehicle control, and message responses was assessed. Results indicated that the type of speech output system affected drivers’ detection of visual changes in the driving environment; they were poorer at detecting these events when either of the synthetic speech systems was used. Drivers detected fewer visual changes during the difficult messages than during the baseline driving. No effects of the speech system type or e-mail message difficulty were observed on the vehicle control measures. Drivers were also less accurate when responding to message content for messages presented in synthetic speech (concatenative) compared with recorded human voice. Subjective ratings indicated that listening to the synthetic speech required more mental effort than listening to the recorded human voice. Preference ratings for the interfaces decreased as mental effort increased. The results indicated that although drivers were not required to direct their attention away from the road, using the speech-based interfaces reduced drivers’ visual event detection and their response accuracy to messages themselves.