Performance on the detection response task during driving: separating the manual and cognitive element of the secondary task

The Detection Response Task (DRT) is designed to measure driver distraction from secondary tasks. This driving simulator study compared drivers’ performance on the head mounted version of the DRT during dual task conditions (DRT + driving) with performance in a tertiary task setting (DRT + driving + secondary task). Three secondary tasks were used, requiring: nonvisual, visual, or visuomanual resources. The 1-back (Easy) and countback in 7s (Difficult) tasks were used as two levels of a nonvisual task. For the visual and visuomanual task, a visual search display was presented on the simulator screen, which overlapped with the back of a lead car. Response to this task was either verbal (visual) or via buttons on the steering wheel (visuomanual). Results showed DRT to be sensitive to the different difficulty levels of the nonvisual task. DRT performance did not distinguish between different perceptual demands of the visual task, but was affected by the manual load of the visuomanual task. Understanding the role of task pace in these studies is thought to be an important factor and further work using different visual tasks is also required to appreciate the value of the DRT in evaluating the distracting effects of in-vehicle HMI.