Love a good optical illusion, don’t you?

The image looks like a spiral, but it's actually a series of concentric circles. Try counting them without touching the screen.

The illusion happens when our visual system receives contradictory stimuli, telling us both 'circle,' and 'spiral.' The angle of the slant in the black and white squares is consistent with what we expect in a spiral. The orientation of the squares alternates from circle to circle, and that contrast alternates from square to square within each circle. Head hurting.

The image comes from a 2002 academic articled entitled Shifts of Edges and Deformations of Patterns by Baingio Pinna and Richard L Gregory and is officially called "Pinna’s Illusory Intertwining Effect”.

Pinna, a professor of pyschology in the Department of Biomedical Studies at the University of Sassari in Italy, lists a range of research interests in his CV that include: perception, visual illusions, psychophysics and experimental phenomenology of visual processes, perceptual organization, vision science of art, and visual design.

Which all goes to show that there are people in the world specialising in all manner of fascinating stuff.
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References

Pinna B, Gregory RL. Shifts of edges and deformations of patterns. Perception. 2002;31(12):1503-8. PMID: 12916675
opticalillusion.net/optical-illusions/pinnas-intertwining-illusion
creativebloq.com/news/optical-illusion-spiral-circles

Images

1. Pinna's Illusory Circle. Image Credit: Pinna & Gregory, 2002.
2. Pinna's Illusory Circle | The Reveal. Image Credit: Pinna & Gregory, 2002.
3. Baingio Pinna. Department of Biomedical Sciences, University of Sassari, Italy.