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(© 2010 Peter Meilstrup & Michael Shadlen)
We show an array of moving spots. Each spot travels in a spiral counterclockwise towards the center of the screen, but contains a grating that moves opposite to its direction of travel. When each spot is by itself its direction of travel is clear. But when we arrange the spots so they are closer together on the screen, they appear to move in different directions — either inward or outward, and either clockwise or counterclockwise, depending on how we arrange them. The proximity of each spot to its neighbors “steers” the perceived direction of motion.
The steerable spiral,
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