Pinna-Brelstaff Illusion

Author

Eric W. Weisstein
August 31, 2026

This notebook downloaded from https://mathworld.wolfram.com/notebooks/RecreationalMathematics/PinnaBrelstaffIllusion.nb.

For more information, see Eric's MathWorld entry https://mathworld.wolfram.com/PinnaBrelstaffIllusion.

Copyright 2026 Wolfram Research, Inc. except for portions noted otherwise

Figure

Fixate the central point and move toward or away from the figure; the two rings appear to counterrotate.

Module[{tile, ring, vertices}, vertices = {{-0.24, 0}, {0, 0.13}, {0.24, 0}, {0, -0.13}}; 
   tile[position_, angle_] := GeometricTransformation[{{GrayLevel[0.55], Polygon[vertices]}, 
      {White, AbsoluteThickness[2.2], Line[vertices[[{1, 2, 3}]]]}, 
      {Black, AbsoluteThickness[2.2], Line[vertices[[{3, 4, 1}]]]}}, 
     TranslationTransform[position] @* RotationTransform[angle]]; 
   ring[radius_, count_, tilt_] := Table[tile[radius*{Cos[theta], Sin[theta]}, 
      theta + Pi/2 + tilt], {theta, 0, 2*Pi - 2*(Pi/count), 2*(Pi/count)}]; 
   Graphics[{{GrayLevel[0.5], Rectangle[{-3.4, -3.4}, {3.4, 3.4}]}, ring[1.9, 28, Pi/9], 
     ring[2.75, 34, -Pi/9], {Black, Disk[{0, 0}, 0.07]}}]]