Probably everybody has at least some experience with the GPS-based personal navigation aids. They usually provide directions using voice prompts and information displayed on LCD screens. While such devices appear to be less distracting to use than paper directions, in-car displays may distract drivers from their primary task, driving.

In order to assess how different in-car navigation aids affect driving performance and visual attention, we conducted an experiment using our high-fidelity driving simulator. The simulator is also equipped with an eye-tracker which provides information about subjects’ visual attention. The following picture illustrates how the experimental setup looked like.

There were three navigation aids that subjects tested in this experiment: paper directions (turn-by-turn directions with a map printed on a sheet of paper), standard PND directions (a map displayed on an LCD screen with turn-by-turn directions delivered through voice prompts), and voice-only directions (just voice-delivered turn-by-turn directions). Participants were driving on a two-lane city road with markings and a light traffic was introduced. The following picture shows one snapshot from the simulation.

We recorded three measures of driving performance from our driving simulator: lane position, steering wheel angle, and velocity. Higher variances of these variables represent worse driving performance. We also calculated the percent dwell time on the outside world for each subject using the data collected by the eye-tracker.

Our results showed that using paper directions degrades driving performance (lane position variance, steering wheel angle variance, and the mean velocity were significantly different between the paper and other navigation aids) and visual attention significantly more than using either a navigation device that provides voice prompts with a map or a device that provides voice prompts only.

Regarding the visual attention, the time participants spent looking at the road ahead was significantly higher when using the voice-only aid than when using either the paper or the voice and visual aid. On average participants spent around 94% of time looking at the road when using the voice only aid and around 89% when using the voice and visual aid.

While these findings supported our hypotheses, one interesting thing was that the majority of the participants expressed that they would prefer using the navigation aid which provides both the visual and voice directions. Based on this, we propose for our future work to model the glancing behavior of the drivers, which would enable us to predict when one would require next instruction, so we would be able to issue a voice prompt. This in turn would enable drivers to keep their eyes on the road at all times, while still being able to have the next instruction in a timely manner.

Lots of other experiments regarding this issue will follow, so we’ll keep you posted!

Zeljko Medenica

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