A Dancer Without A Body

A reader sent in a link to this piece of Flash artwork, Drift. The globes dance and drift, moving together in such a way as to suggest a person. The science behind this is discussed in Hack #77 ‘See A Person In Moving Lights’.


The short story is that the way our brains pick out the principle components of moving people allows us to project a really powerful illusion of personhood onto lights that move in just the right way (the right way being the way lights would move if they are put on someone’s joints). It is moving together in time that creates the illusion, which is why this screenshot won’t convey any of the power of the illusion and you’ll need to watch the movies if you want to see exactly what i’m talking about.

The interesting thing about the Drift animation, I think, is that although it is elegant and at times evocative it isn’t quite convincing. Two reasons for this are, I think, that a) the balls are quite large and so do not precisely indicate a point on the body and b) this is an animation of how someone thinks someone’s joints should move, not a recording from real joints. Compare with these Dancing Lights which are done with real people in darkness with lights attached to their joints. Although, in some senses, there is less information here, the illusion is so much, so much, more convincing. There is a shock of recognition that you just cannot deny “Yes”, my brain says, “These are definitely real people, not just a collection of lights”. But you are not seeing real people, you are seeing a collection of moving lights. It is impossible to perceive it any other way that as people thought- every nuance of motion and timing is rendolent of personhood. The illusion in the animation suffers because it doesn’t capture these small things and the brain knows the difference.

And, finally, my favourite link : The BioMotion Lab Point Light Walker of Prof. Nikolaus Troje. This demo, constructed using recordings from scores of real people, allows you to adjust the gender, build, and mood (both nervous-relaxed and happy-sad) of a set of walking lights. Playing with this you can see just how much information we can get out of this abstracted-kind of motion.

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