Which way are the two sets of spheres rotating when you look at the red dot. What about the yellow dot? Are they moving the same way? Different ways?
The ambiguity in this demonstration is due to how the foveal region (center) of our vision and our periphery (outer regions) “process” information somewhat differently. While indeed the peripheral regions of the retina have poorer spatial resolution than the foveal region—hypotheses on the “how” of this illusion push past that simple difference. At the 2008 Society for Neuroscience conference, researchers Shapiro, Knight, and Lu hypothesized that the machinery of the foveal visual system allows us to represent multiple features simultaneously, but this machinery is absent in the periphery. Thus, the peripheral visual system seems to yield a much different visual response than what is found with the fovea.
To better explain–when something is at the center of your vision, we tend to focus on certain features over others. In this case, your foveal vision favors the so-called “bulk-motion” of the animation. However, when that something is more near the edge of your vision, those features favored by the fovea may be abstracted or compressed, thus causing us to potentially focus on another type of feature–producing a much different perceptual result. So when you look right at a ring of circles, your brain favors the BULK motion (you see the circles moving counterclockwise.) The motion of the pattern of stripes on each sphere looks more like flickering than movement. But when you see the animated ring in your periphery, the clockwise PATTERN motion of the other ring gets your brain’s attention, not the bulk motion (again, a different feature). So suddenly you see the circles moving in the same direction as the pattern: clockwise.
Pretty neat eh?
To learn more about this particular demonstration:
The above demonstration has been developed independently in two laboratories, and was presented by both laboratories at the Society for Neuroscience conference in Washington, D.C., in November 2008.
Arthur Shapiro, Emily Knight, Zhong Lin Lu, presented this demonstration in the 2008 Best illusion of the year contest and as an extension of our work on “feature blur” in the visual periphery.
Peter Meilstrup and Mike Shadlen presented their version of the illusion as part of a continuation of Shadlen and Movshon’s work on motion signals in the brain (specifically, in area MT of the visual cortex). Here is a link to Professor Shadlen’s webpage.
To learn more about the effort of Arthur Shapiro: http://www.shapirolab.net/