Three types of expanding/contracting optic flow patterns are shown below. Each has a different speed profile, which results in differentially perceived rigidity, and sense of self-motion induced by the movies. These movies are extended versions of those that can be found in the supplemental materials of: Holten, V, Donker, SF, Verstraten, FAJ & van der Smagt, MJ (2013):” Decreasing perceived optic flow rigidity increases postural sway”, Experimental Brain Research, DOI 10.1007/s00221-013-3543-z.
Demos courtesy of Vivian Holten.

NB: These movies are rather small (yet about 20 MB each), so do not sit too far away from the monitor (you might want to right-click and download them first). In our experiments the stimuli subtended 87×56 degrees visual angle.

Single Speed
No speed gradient, but with a constant angular retinal speed. Dots appear to move faster in the center.

Linear Speed Gradient
The linear speed gradient simulates the movement of a fronto-parallel plane towards or away from the observer.

Quadratic Speed Gradient
The quadratic speed gradient simulates observer movement through a circular tunnel.

The movies are set to loop back and forth, but this may not work automatically on every system.