James Fraser
The twisted-cord illusion, 1908
British psychologist who in 1908 described the twisted-cord illusion, concentric circles that appear to spiral inward.
Fraser Spiral
Concentric circles built from leaning cords. Trace one with a finger and it closes; let go and it winds inward again.
About this pattern
James Fraser, 1908
Fraser's twisted cord: each ring is made of short segments set at an angle to the ring itself, on a background that alternates with them. Local tilt is pooled along the contour before the shape is judged, so the accumulated lean is read as a slow change of radius. The circles are exact. Setting the lean to zero collapses the spiral instantly, which is the quickest way to prove it to yourself.
Behind the mathematics