How many limbs are required for a robot to give the impression of human behavior?

One of my inspirations for this project was a program created by Hal Eagar … a series of simple geometric shapes, circles or squares, animated by algorithmic rules to resemble behavior. It was suprisingly effective … you could definitely read the beginnnings of action and character into the movements of the shape.

Hal also added your choice of music genres. Hearing the music made the algorithmic behvior into a scene … each composition had a particular emotional tone and dramatic feeling, which radically changed how you perceived the intentions and behavior of the shapes.

So in theory, no limbs are required … a simple circle (or basic robot with wheels) would be sufficient. But a pair of arms would add expressive possibilites, and shift the robot closer to anthropomorphism. Are legs equally anthropomorphic? My impression is that they are secondary, but that might be because I haven’t seen a good robotic implementation, or a theatrical example where legs alone were used for expression.

What about a head and/or neck? Head and neck have many expressive degrees of movement which can be simulated by whole-body movement, but with less depth and subtlety.

What about fingers and toes? Fingers definitely, but toes less so … although again we seldom see them used expressively, so it might be an under-utilized opportunity. (The four-fingered creations of Disney animators are an interesting variation.)

So here’s a rough theory: 0 limbs are okay, but more limbs add more expressive power and anthropomorphic possibilities, in approximate proportion to the number of limbs. (It would be interesting to explore strange combinations … one arm and one leg, for example.)

But how far can we go? It seems to me that a greater number of limbs than the human norm gradually erode the anthropomorphism. And a very large number of limbs (a 100-limbed octopus, for example) begins to reduce the total expressiveness to something closer to the original circle.

Hmmm … there’s an equation here somewhere. If I figure it out, I’ll add it to the post. If somebody else figure it out, please comment!