I wasn’t sure where exactly to put this. Just a brief thought experiment I thought I would share with respect to the sensorimotor aspects of the brain. I’m not at all confident in neuroscience or the current theory on the sensorimotor interface. But this thought experiment is interesting so I thought I’d share. It’s the “Unhappy Child” thought experiment.
Suppose a baby is born in the unfortunate circumstance of having only outgoing signals to the muscles from the brain, but no incoming signals from the muscles to the brain. The directions are with respect to the brain. So if the child were to move, they would have no direct indication of knowing they were moving. The only way to know is to use senses other than touch, like sight.
Here is the question: Will the child ever move?
A similar question was asked by a philosopher once upon a time (can’t remember who) but this draws a slightly different conclusion that is important for understanding how we move. I propose that the answer is no, the child will never move. With no previous experience “exercising” the brain activity (synaptic firing or what-have-you) used for movement, the child will remain oblivious to the fact that it could move.
If this is true, then it indicates that all movement is reactionary by nature, and that movement is dependent on first receiving input from the motor-related muscles and bits before it can give output.
This is not the answer, of course. While there is a definite answer, for now it is merely a philosophical question. As support for the idea that you need input from your muscles before you can use them, consider trying to wag your tail or wiggle your ears. For those of us not gifted with a tail or the ability to wiggle our ears, it is impossible to imagine moving them. We can see our ears, but without muscular input there’s no way for us to move them.
For this to stand as an analogy we would have to assume the ears have muscle, but the concept is really about anything we can’t move, whether it exists or not.
Perhaps the child will move, though. Then we can imagine that the movement would be random and may potentially result in exhaustion and death. That kid is quite unhappy. But we can support the idea that the child will move by considering a baby born into space - no gravity or physical contact, it simply comes into being. We would imagine the baby would move its arms around and learn of them, along with its head and legs and torso.
We might consider the fact that all muscles are constantly sending inputs to the brain, though, so we should stick to the baby born without “feedback” from its muscles.
If it were true that sensory input is required in order to be able to move, then this has obvious implications for a sensorimotor computer. The motors themselves must be able to act as inputs to the sensorimotor region in order for the program to use those motors, and it would use those motors by firing neurons and receiving feedback again.
Another consideration in the thought experiment is involuntary muscle movements such as those in the heart etc. I’m sure there are plenty more aspects I’m missing, as well. But I hope this helps people consider how the sensorimotor mechanisms behave a little better. If you have a different opinion, then by all means, have a go!