Using hierarchical task analysis to compare four vehicle manufacturers’ infotainment systems

September 2013

Mobile technology has become pervasive in the driving environment, and its use has been linked to increased crash risk. Of particular concern are devices that place visual-manual demands on drivers. In response, auto manufacturers have started equipping vehicles with technology that allows occupants to interact with manufacturer-installed functions and portable devices using speech commands instead of traditional visual-manual inputs. Although voice interfaces alleviate competition for visual resources, they impose cognitive demand that can degrade driving performance, especially if they are too demanding. Hierarchical task analyses were performed for a set of in-vehicle tasks using visual-manual and auditoryvocal interfaces for four different production systems in 2013 model year vehicles to assess the number of steps required to complete the tasks. In general, tasks performed using voice interfaces could be completed in fewer operations than when performed visual-manually. However, in some instances, the voice interfaces required more operations than the visual-manual interfaces. The additional operations resulted from the inability to chain multiple speech commands and verification of speech commands. Allowing chained voice commands reduces the number of operations required to complete a task and should reduce task time and overall cognitive demand. Verification steps likely reduce error but may impose a greater working memory load than generating speech commands and, in some cases, may exceed the limitations of working memory. The findings from this study will be used in a larger field study examining cognitive demand associated with different voice interface designs and the effect on driving and secondary task performance.