Sandrine Ceurstemont, editor, New Scientist TV
Think an object can't be in two places at once? This animation shows how the perceived location of a dot is influenced by what's happening around it.
In this video, a flashing dot is surrounded by two diamonds that shift across the screen. When they move horizontally, the dot seems to shift sideways and slightly upwards. In a second version, in which the corners of the diamonds are obscured, the dot appears to move diagonally. In fact, the dot never changes place.
The illusion is the work of Peter Kohler from Dartmouth College in Hanover, New Hampshire, and his team. Kohler has been trying to determine if the dot's perceived shift in position is caused by the overall motion of the diamonds or that of its components. For example, although the shapes as a whole are moving sideways, viewing the edges in isolation shows that segments of the diamonds are moving upwards. "Our results show that global motion does influence the shift," he says. "But the fact that even the unoccluded diamond does not yield a purely horizontal shift indicates that local signals are also very important."
The team now plans to investigate how quickly our brain perceives the shift. "Integration of local and global motion is known to take about 150 milliseconds," says Kohler. "It would be interesting to see if the effect takes a similar amount of time to kick in."
By presenting the illusion for very short amounts of time, the researchers will be able to determine if different versions are initially perceived in the same way. "We also have fMRI work under way to identify brain areas that represent the perceived shifted location rather than the actual location," says Kohler.
The illusion was recently presented at the European Conference on Visual Perception in Alghero, Italy.
If you enjoyed this brain trick, check out our previous Friday Illusions to see, for example, how you can control an animation with your mind.
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