Here is a sneak preview of one the illusions that my laboratory will be presenting at the Neural Correlate Society’s “Best illusion of the year” contest that will be held next week (May 11th ) in Naples, Florida. The illusion was devised to investigate questions related to contrast and visual grouping (see article).
Warning: the illusion involves rotating, high-contrast diamonds. If you are prone to migraines or epilepsy, or get motion sickness, please do not stare at this illusion.
[The illusion is a flash file and will not appear in an RSS feed]
Description: You are looking at columns of pink and yellow diamonds separated by columns of spinning black/white/gray diamonds. The pink diamonds appear to move to the right; the yellow diamonds appear to move to the left.
There are two main things to notice about the display:
1. The pink and yellow columns are not really moving. Don’t believe me? Click and drag the spinning black/white/gray diamonds to move them out the way. When you do, you will see that the spinning diamonds are placed on top of a completely stationary colored background.
2. The motion is perpetual. The pink and yellow fields seem always to be headed towards (or away from) each other, but they never meet (and they never grow farther apart). This aspect of the effect can be quite mesmerizing, so be careful.
The motion originates from the edges between the spinning diamonds and the colored fields. The edges of the diamonds are tilted at -45 or 45 deg; the motion, therefore, should always shift in an oblique direction. To get a better handle on this, click the “add/remove diagonal bars” button. The diagonal bars cover up opposite sides of the rotating diamonds so that only every other edge is shown. When the diagonal bars are present, the pink and yellow fields move diagonally.
Why, then, should the pink and yellow fields appear to move horizontally when the diagonal bars are not present? Not to be too technical, but it seems to me that either the visual system is computing motion for the colored diamonds from a vector sum of the motion at the edges; or the visual system is using the information at the edges to define an object (in this case, a diamond), and motion for the object takes precedence over the motion that originates at the edge.
I have also included a button that allows you to “add/remove horizontal bars.” The horizontal bars stretch across the image so that the colored diamonds turn into colored triangles. Nonetheless, instead of seeing individual triangular segments, you perceive the image as a series of colored diamonds that appear to move behind a bar. It is as if the visual system joins the triangles to form the diamonds, so that you perceive a "whole" object.