Tuesday, August 27, 2013

The Other Facet of Motor Learning, Part I

Part I, II


In a previous two-part article titled Goal-Oriented Motor Learning, I wrote the following:
The Two Facets of Motor Learning

I will not go into how the brain learns sensory patterns in this article. I will, one day, but not today. What I will explain in this article is one facet of motor learning, the one that leads to goal-seeking behavior. There is another facet that has to do with eliminating motor conflicts. That, too, will have to await a future article. I just want to explain how the brain finds the right motor connections for goal-seeking behavior. As I wrote previously, I get my understanding of the brain by consulting an ancient oracle (no, I was not joking) and interpreting its message the best I can. Here's what the oracle says about goal-oriented motor learning:

Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols.
I always burst out laughing every time I read this verse in the book of Revelation. I laugh, not just because I think the wording of the verse is hilarious, but because the choice of metaphors is so exquisitely brilliant. Jezebel is a metaphor for a predictive mechanism. This is why she is called a prophetess. That's an easy one to interpret. But the mechanism is not a good predictor because, during its attempt to achieve various goals, it causes bad things to happen along the way: fornication and idolatry. Fornication is the oracle's metaphor for making connections that cause motor conflicts, a topic for a future article. Idolatry (the worshiping or serving of other gods) symbolizes the making of connections that lead to the wrong goals. Obviously, neither fornication nor idolatry will be tolerated. :-D
I went on to explain that a goal is a pattern and that goal-oriented motor learning consists of choosing the right connections between pattern-associated motor neurons and the target motor effectors. During this trial and error learning process, the idolaters, i.e., the motor connections that fail to satisfy their associated patterns, are simply disconnected. But there is a little bit more to motor learning than just achieving goals. Below, I explain the other facet of motor learning, the one that the oracle metaphorically calls fornication.


Fornication, as used in the Bible, is the act of having sex with a woman who is someone else's wife. It's a conflicting act. In the quoted passage above, the oracle is using fornication as a metaphor for motor conflicts in the brain. Motor conflicts are a problem because there is a fixed number of actuators (i.e., muscles) that must be shared by a huge and growing number of competing sensorimotor entities (neural programs) in the cortex. Obviously, if two or more entities try to use the same actuator simultaneously, conflicts will arise which will cripple any kind of goal-directed behavior.

The Simplicity and Power of Motor Learning

The motor learning system I described above uses a trial and error process to find appropriate motor connections. New connections are made randomly and an error detection mechanism is used to weed out idolaters and fornicators. This system ensures effective and smooth motor coordination. Robots will use it to learn sophisticated motor behavior such as walking, driving, speaking, etc. The simplicity of it all is unnerving, some would say, but its power is in the simplicity. In Part II, I will go into the details of conflict detection and elimination. Coming soon.

See Also:

The Holy Grail of Robotics
Goal Oriented Motor Learning
Raiders of the Holy Grail
Secrets of the Holy Grail

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