This is a demonstration of silencing, described in:
Suchow, J.W., & Alvarez, G.A. (2011). Motion silences awareness of visual change. Current Biology. doi:10.1016/j.cub.2010.12.019
Instructions: Keep your eyes fixed on the small white mark in the center. At first, the ring is stationary and it's easy to tell that the dots are changing. A few seconds later, the ring begins to rotate and the dots suddenly appear to stop changing.
But play the movie again, this time looking directly at one of the dots and following it as the ring rotates. You will see that, in fact, the dots had been changing the whole time, even during the rotation—you just didn’t notice it. This failure to detect that moving objects are changing is silencing.
The full set of demos, and a reprint of the paper, is available at http://visionlab.harvard.edu/silencing/.