What to do
Follow the red dot with your gaze (head rotation helps). Observe that some of the squares in the background seem to shift. The effect is fleeting for me – sometimes strong, sometimes missing. But all motion here –apart from the red dot– is illusory.
What else to do & observe
With the popup menu, select Lanes rather than Circle. Many more settings wait for you to play with them (“Ranomize” is not useful yet).
Comment
This is a variant of the Pinna-Brelstaff illusion which already appeared in their 2000 paper. The same explanation applies.
Sources
- Pinna B, Brelstaff GJ (2000) A new visual illusion of relative motion. Vision Res 40:2091–2096 [PubMed]
- Comments by Ben Backus
- More sources on the other Pinna-Brelstaff page.