The Effects of a Production Level "Voice-Command" Interface on Driver Behavior: Summary Findings on Reported Workload, Physiology, Visual Attention, and Driving Performance

This report summarizes key results of an on-road study assessing perceived workload, physiological arousal, visual attention, and basic driving performance metrics while drivers engaged in a number of tasks with a production version, in-vehicle voice-command system. The same metrics were also evaluated while participants carried out an implementation of the manual radio tuning reference task (Driver Focus-Telematics Working Group, 2006) and three levels of an audio-presentation / verbal response delayed digit recall task (n-back) that is known to produce graded levels of cognitive demand. Extensive training on all tasks was provided prior to assessment under highway driving conditions. Results for an analysis sample of 60 drivers, equally distributed across both genders and two age groups (20-29 and 60-69), are summarized here and presented in detail in an associated technical report (Reimer, Mehler, Dobres, & Coughlin, 2013). Depending on the task assessed and measure evaluated, both positive features and concerns associated with the use of the voice interface were identified. Physiological arousal during the voice tasks was comparable or lower than that observed during the more difficult level of manual radio tuning task as measured by skin conductance and heart rate, respectively. Perhaps most notable was the identification of a high level of visual demand / engagement during selected tasks, such as the use of the voice-command interface for entering addresses into the navigation system. It also appeared that different age / gender groupings tended to interact with the voice system in different ways. These findings highlight that implementations of voice interfaces can be highly multi-modal and are not necessarily free of visual-manual demands on attentional resources. If one were to apply the current National Highway Transportation Safety Administration (NHTSA) visual-manual distraction guidelines to the tasks assessed, a number of "voice" interactions would not meet the total off-road glance time criteria of the guidelines. While these data were not collected in full alignment with NHTSA's simulation- based guidelines, the overall structure and metrics are similar, and so this work raises a number of important questions. It is clear that visual demand needs to be considered in the design of multi-modal voice interfaces. This highlights the question of how an acceptable level of visual demand should be defined in the context of multi-step and extended task time interactions that characterize activities involving voice-command interfaces. Finally, the results illustrate the necessity for additional research assessing the generalizability of these findings to other production level and hand-held "voice" interactions, and in developing methods of quantitatively assessing the net attentional costs and benefits of providing drivers with information across different modalities. Voice interactions can play an important role in the vehicle environment. Optimizing the selection of activities in which the driver utilizes voice interaction and the appropriate design of displays will help to maximize driver attentional focus towards information necessary for vehicle operation, while allowing, where appropriate, interactions with interfaces for comfort, convenience and communication functions.