A Secondary Assessment of the Impact of Voice Interface Turn Delays on Driver Attention and Arousal in Field Conditions

Voice interface use has become increasingly popular in vehicles. It is important that these systems divert drivers’ attention from the primary driving task as little as possible, and numerous efforts have been devoted to categorizing demands associated with these systems. Nonetheless, there is still much to be learned about how various implementation characteristics impact attention. This study presents a secondary analysis of the delay time between when users finish giving commands and when the system responds. It considers data collected on 4 different production vehicle voice interfaces and a mounted smartphone in field driving. Collapsing across systems, drivers showed an initial increase in heart rate, skin conductance level, and off-road glance time while waiting for a system to respond; a gradual decrease followed as delays continued. The observed attentional and arousal changes are likely due to an increase in anticipation following a speech command, followed by a general disengagement from the interface as delay times increase. Safety concerns associated with extended delay times and suggestion of an optimal range for system response times are highlighted.