Morphological computation

Morphological computation is the term used to describe computation which is obtained through interactions of physical form.

Birth of the phrase Morphological Computation
The phrase morphological computation was first coined by Chandana Paul 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 perform computation.

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 of a robots 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 first proof that physical interactions in robot morphology could give rise to computation. Paul coined the term "morphological computation" to describe this phenomena.

Relevance
The understanding that simple physical interactions can give rise to computation has far-reaching implications in many domains, which are only beginning to be understood.

Robotics
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.

This provides the basis for a new field of research, in which theoretical methods can be developed to analyze and quantify the relationship between morphology and control

Based on such analysis, 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. .

Note: Some people in robotics use the phrase "morphological computation" in a broad sense as describing the trade-off between morphology and control in robots. That is, every instance in which the robot morphology is shown to aid the control, they say the body performs "morphological computation". This is technically inaccurate, as there are other mechanisms besides computation which can also give rise to the morphology and control trade-off. Without an analysis which proves the existence of computation in the specific robot structure, it is not accurate to claim that it performs morphological computation.

Artificial Intelligence
The understanding that simple 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.

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.

The relevance of morphological computation in adaptive behavior and cognition has been more extensively demonstrated with various examples of robots interacting in the real world

Molecular Processes
The only significant physical characteristics of Paul's XOR 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.

Biomechanics
It has been found that the musculo-skeletal systems of biological organisms also embody the necessary characteristics to enable computation. 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.

Events
The first international event on the topic of morphological computation in robotics was the International Workshop on Morphology, Control and Passive Dynamics, held at the Intelligent Robots and Systems Conference (IROS) in Edmonton, Canada, June 2005. This was organized by Chandana Paul, Andy Ruina, Max Lungarella, Manoj Srinivasan, and Fumiya Iida, and addressed the role of morphological computation in robot control, particularly in underactuated motion.

Following this, the First International Conference on Morphological Computation was organized by Rolf Pfeifer, Norman Packard, Mark Bedeau, and Fumiya Iida in Venice in March 2007. This was a more general event covering morphological computation in a wider range of areas such as robotics, amorphous computing, organic computing, membrane computing, DNA-computing, self-assembled computing and molecular computing. .

A course on Morphology and Computation is organized by Lukas Lichtensteiger at the University of Zurich, Switzerland. This course covers morphological computation and related topics in robotics and biomechanics, as well as in organic and molecular computation. The course was taught for the first time in February 2006, and received a positive response. It has been offered again in February 2007.