Convex rear view mirrors compromise distance and time-to-contact judgements

Abstract

Convex rear view mirrors increasingly replace planar mirrors in automobiles. While increasing the field of view, convex mirrors are also taken to increase distance estimates and thereby reduce safety margins. However, this study failed to replicate systematic distance estimation errors in a real world setting. Whereas distance estimates were accurate on average, convex mirrors lead to significantly more variance in distance and spacing estimations. A second experiment explored the effect of mirrors on time-to-contact estimations, which had not been previously researched. Potential effects of display size were separated from effects caused by distortion in convex mirrors. Time-to-contact estimations without a mirror were most accurate. However, not distortion, but visual angle seemed to cause estimation biases. Evaluating advantages and disadvantages of convex mirrors is far more complex than expected so far.

Keywords:

• Rear-view mirror
• Convex mirrors
• Time-to-contact
• Distance estimation

Acknowledgements

We are grateful to the Schott glass company of Mainz, Germany for supplying the convex mirrors. Agnes Münch programmed the TTC displays and Matthias Gamer and Daniel Oberfeld-Twistel provided valuable help during planning and data analysis. Finally, we thank all volunteers who served as observers.