Friday Illusion: 100-year-old quilt reveals 3D vortex

Sara Reardon, reporter

You might not expect a mind-bending vortex to emerge from an old quilt. But about 100 years ago, a housewife armed with a needle and some red and white scraps of cloth crafted a unique pattern that doubles as a brain trick.

Recently discovered at a quilt show in New York City by Eric Altschuler from the University of Dentistry & Medicine of New Jersey in Newark, the patchwork appears to be made up of spirals that descend into a 3D vortex in the middle. But in fact the red and white rectangles in the pattern are arranged in concentric circles that decrease in size and thickness as they approach the center.

To study the effect, Altschuler and his students have now recreated the pattern using software. By producing a version where the circles don't get thinner (see video), the team found that the image still seems to spiral but no longer looks three-dimensional. When viewed in peripheral vision, the spirals are initially visible but quickly vanish.

The contrasting red and white colours also affect the illusion of depth. When a green hue that's just as bright as the red is substituted for the white, the spirals become flat. But if the red is dimmer than the green, or vice versa, the vortex returns. This shows that without contrast, depth cues are lost.

According to Altschuler, the phenomenon is a result of the gestalt effect, whereby we tend to visually group a collection of features into a larger shape. In this case, our brain creates the smoothest path between diagonal red blocks, which therefore appear to be connected, creating the illusion of curved arms. The effect is especially pronounced when looking at the smaller blocks near the centre: larger pieces further out are more likely to be perceived as distinct objects.

Altschuler recently presented his findings at the annual Society for Neuroscience meeting in New Orleans, Louisiana. The maker and origin of the quilt are still a mystery but the butterfly designs in the corners suggest it was made between 1890 and 1910.

If you enjoyed this effect, check out our previous Friday Illusions to see for example, a snake that seems to slither or a gravity-defying roof.

Congratulations to Simon Wilcox, the winner of last week's challenge, who was the first to correctly point out that there is no mirror in the video. What appears to be a reflection is simply Richard Wiseman using his left hand, with everything else well-placed to simulate a mirror image.

Source: http://feeds.newscientist.com/c/749/f/10897/s/265d4002/l/0L0Snewscientist0N0Cblogs0Cnstv0C20A120C120Cfriday0Eillusion0E10A0A0Eyear0Eold0Equilt0Ereveals0E3d0Evortex0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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