Masking Action Relevant Stimuli in dynamic environments – The MARS method

• The MARS method allows determining the information demand drivers have for an action relevant stimulus.
• The number of button presses to unmask a stimulus is measured as dependent variable.
• The traffic light is masked during intersection approaches.
• The number of button presses to unmask the traffic light is sensitive to variations in the track.
• The MARS method can be extended to various stimuli in the traffic environment and in-vehicle devices.

We present the novel MARS (Masking Action Relevant Stimuli) method for measuring drivers’ information demand for an action relevant stimulus in the driving scene. In a driving simulator setting, the traffic light as dynamic action relevant stimulus was masked. Drivers pressed a button to unmask the traffic light for a fixed period of time as often as they wanted. We compared the number of button presses with the number of fixations on the traffic light in a separate block using eye tracking. For the driving task, we varied the road environment by presenting different traffic light states, by adding a lead vehicle or no lead vehicle and by manipulating the visibility of the driving environment by fog or no fog. Results showed that these experimental variations affected the number of button presses as dependent measure of the MARS method. Although the number of fixations was affected qualitatively similar, changes were more pronounced in the number of fixations compared to the number of button presses. We argue that the number of button presses is an indicator for action relevance of the stimulus, complementing or even substituting the recording and analyses of gaze behaviour for specific research questions. In addition, using the MARS method did not change dynamic driving behaviour and driving with the MARS method was neither disturbing, nor difficult to learn. Future research is required to show the generalisability of the method to other stimuli in the driving scene.