Study of Driver Distraction Due to Voice Interaction

A new telematics service has been launched by Nissan in the Japanese market that combines text-to-speech (TTS) technology with the communication function of a cellular phone. With this service, drivers operate their in-vehicle information system by simple voice commands, download news and the latest information from a portal site to the system via a cellular phone, and have the information read to them by the TTS synthesizer, thereby obtaining the desired information without relying on their visual processes. This paper describes the tests that were carried out in the course of developing the system to determine its potential influence on drivers' mental distraction. Tests were conducted with a driving simulator and an actual vehicle, with participation by twenty subjects, including five women. Both the driving simulator and actual vehicle were equipped with steering wheel buttons and an instrument panel LED that illuminated at random intervals during the driving tests. The subjects were instructed to follow a preceding vehicle and to press the steering wheel button when the LED illuminated. In addition, they were also given a simultaneous information device task such as listening to a prerecorded radio broadcast or news read aloud by the TTS synthesizer, viewing the navigation display or talking on a cellular phone. Their response time to the illumination of the LED was measured under these conditions. Vehicle data were also recorded to determine the amount of lateral lane displacement and change in the headway distance that occurred at the time the information device tasks were performed. The indexes were then compared for the different information device tasks assigned. The results obtained for all of the indexes showed that the mental distraction level when listening to a TTS reading of information was comparable to that of listening to the car radio.