Karen De Valois

About Karen De Valois (Edit profile)

Karen K. De Valois is Professor of Psychology and Vision Science at the University of California, Berkeley (valois@socrates.berkeley.edu).

In the Dark: Seeing Bikes at Night

Karen De Valois , Tatsuto Takeuchi, and Michael Disch

It's midnight. You’re driving home after an evening out, when you notice a small bright object—or perhaps two—moving across your field of view in an odd scalloped pattern. Because you have seen one before, you may recognize it as the reflector on the wheel of a bicycle approaching on an intersecting street. You must quickly decide whether to stop, slow down, speed up, or continue at the same speed. To make that decision correctly, you must know not only how fast you are moving, but also when the bicycle will enter and leave the intersection. This is considerably more difficult than you may think.

Download the PDF.