Morphological computation
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Morphological computation is the term used to describe computation which is obtained through interactions of physical form. This unique phenomena, which was discovered by Chandana Paul in 2002, leads to the possibility for simple interactions in physical systems to give rise to computational effects. These effects can be observed in more than one domain including the physical bodies of robots, embedded systems, molecular dynamics, biomechanics, and cognitive behavior.
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[edit] Discovery of Morphological Computation
The discovery of morphological computation was made in August 2002 in the context of legged robotics. In work on biped robots, Paul had observed that smooth variation of single parameters of an open loop controller, could give rise to discrete changes in limit cycle behavior. Although there was no discrete change specified in the control, the interaction of the controller with the morphology produced a discrete change in behavior, almost as if a bit were suddenly being flipped in the controller. This puzzling phenomena led Paul to question whether it may be possible for the morphology, or the physical body of the robot, to play a computational role in the system.
In August 2002, Paul was reading a book which gave a simple explanation about how perceptron networks could not give rise to functions which were non-linearly separable. This simple fact had been well-established in the past, but it now raised a new doubt. Paul felt that if the morphology could indeed perform computation, then it should be possible to design a robot which used perceptron networks to perform a non-linearly separable function.
She set herself the challenge to design such a robot. After many trials and design iterations, Paul finally discovered the design of the XOR robot. This robot, elegant in its simplicity with only two moving parts, could use perceptron networks to display the non-linearly separable function XOR, in its behavior. The robot represented the discovery and proof that physical interactions in the morphology could give rise to computation. Paul subsequently coined the term "morphological computation" to describe this effect. This was first presented to the Adaptive Behavior community, at the Simulation for Adaptive Behavior Conference in Los Angeles, July 2004. [1]
[edit] XOR Robot
The XOR robot is comprised of a a simple robot chassis with a wheel. The wheel has two motors, one to drive the wheel forward (M1), and the other to lift it off the ground (M2). When the wheel is on the ground and turning the robot moves forward. When the wheel is lifted up, it no longer makes contact with the ground and its motion does not affect the behavior of the robot.
When this simple robot is hooked up to two perceptron networks, such that M1 is connected to a network which computes the OR function, and M2 to a network which computes the AND function, the robot is able to display the XOR function in its behavior. [1]
[edit] Relevance
The discovery that simple physical interactions can give rise to computation has far-reaching implications in many domains.
[edit] Robotics
Robots can be designed which use the morphology to perform a computational role in the system, and the ease the computational requirements on the controller. A nice example of this was provided by Rolf Pfeifer and Fumiya Iida, introducing the idea to the robotics community, through the design of a robotic hand.[2]
The understanding that the morphology performs computation can also be used to analyze the relationship between morphology and control and to theoretically guide the design of robots with reduced control requirements.[3]
[edit] Artificial Intelligence
The discovery that physical interactions give rise to computation opens the door to the possibility that the physical interaction of a robot body with the environment can also be used to enhance its computational abilities. In essence the world can become the "abacus" for the computations of the intelligent agent.[1]
[edit] Cognitive Science
The understanding that the physical body and its interaction with the environment can enhance computational abilities, also opens the door to a new field of investigation in cognitive behavior, into the way humans and animals exploit the environment in their behavior to enhance computation.
One example, of this is seen in counting in humans. When there are a very large pile of coins for example that need to be counted on a table, a person does not rely on pure computational processing of visual input to accomplish the task. Instead they use their hand to physically move the coins one by one from one pile to another all the while incrementing a mental counter. Thus, they utilize the physical interaction with the environment to enhance their computational ability and accomplish an otherwise computationally intractable task.[1]
[edit] Molecular Processes
The only significant physical characteristics of the robot which are necessary to give rise to computation are the interaction between moving parts, and the occurrence of discrete events. Both these features are also found in molecular interactions, and thus it has been proposed that morphological computation can also occur in simple molecular interactions.[3] This understanding could open up a new field of investigation into what kinds of molecular interactions can lead to computation.
[edit] Biomechanics
It has been found that the musculo-skeletal systems of biological organisms also embody the necessary characteristics to enable computation.[3] This understanding could lead to new roads of investigation into how evolution has optimized musculo-skeletal systems to enable computations which help motor control.
Thus, the study of morphological computation is relevant to many areas of science and engineering and will serve to conceptually unify the investigation of many natural and artificial domains.
[edit] References
- ^ a b c d C. Paul (2004) Morphology and Computation, Proceedings of the International Conference on the Simulation of Adaptive Behaviour Los Angeles, CA, USA, pp 33-38
- ^ R. Pfeifer and F. Iida (2005). Morphological computation: Connecting body, brain and environment. Japanese Scientific Monthly, Vol. 58, No. 2, 48-54
- ^ a b c C. Paul (2006) Morphological Computation, Robotics and Autonomous Systems, Special Issue on Morphology, Control and Passive Dynamics, August 2006, 54(8): 619-630
[edit] Further Reading
R. Pfeifer and F. Iida. Morphological Computation for Adaptive Behavior and Cognition. International Congress Series. (2006) 1291: 22-29
