Bicycle Illusion Demo (VSS 2006)

Bicycle illusion demo to accompany Masson et al (2009)

  • Masson, M.E.J., Dodd, M. D., & Enns, J.T. (in press). The bicycle illusion: Sidewalk science informs the integration of motion and shape perception. Journal of Experimental Psychology: Human Perception & Performance. [pdf]

A new look at how shape and motion interact in conscious experience.
The bicycle illusion can experienced by viewing a bicycle moving alongside a fence consisting of a parallel pair of rails that sag between fence posts. The cycle and rider seem to bob up and down with the sagging rails. But, note that you must view the bicycle and the fence from a considerable distance to get this effect. If you get too close, a different illusion may be seen–that of the cycle and rider bobbing in opposition to the sagging rails.

On a computer screen, a version of this illusion can be constructed by moving a small disc in a horizontal direction over a pair of sinusoidal rails. The disc appears to move up and down. From a distance, the disc seems to wiggle within the rails (an illusion of assimilation) but at nearer viewing distances the disc will appear to wiggle counter to the rails (an illusion of contrast).

The bicycle illusion demonstrates that there are situations in which a spatial property of a stationary shape (the rise and fall of the rails) can be misattributed to the motion of a nearby object (the horizontally moving disc). We are currently preparing a paper for publication on this illusion.

View the demo in your web-browser (.mp4 file) *** Animations shown do not represent the actual motions used in the experiment.