Like I suppose every red-blooded male did, I loved anything with wheels when I was a child. I still have a small, now rusting, collection of toy cars that I push around the floor from time to time. My wife suspects I have regressed into childhood; that is, if she can assume I grew out of it at all.
But better men than I remain fascinated with cars too. Example: Valentino Braitenberg of the University of Tuebingen, Germany. In 1984, he wrote Vehicles: Experiments in Synthetic Psychology, a slim collection of thought experiments involving little cars. He uses them to make some interesting observations about human behaviour, much as my wife makes observations about mine.
Braitenberg's imaginary cars all have two things in common: sensors and motor-driven wheels. The sensors respond to light and send signals to the motors. His simplest vehicle, Vehicle 1, has one sensor and one motor driving one wheel. The more light the sensor picks up, the faster the motor turns, propelling Vehicle 1 in whichever direction it happens to be pointing. It speeds up in well-lit areas, slows down in dark ones. In outer space, Vehicle 1 would move in a straight line, varying its speed as it passed sources of light.
But when Vehicle 1 must contend with friction, as it would on Earth, it deviates from a straight line in unpredictable ways. Responding to light and dark, driven by its motor, disturbed by the forces of friction, Vehicle 1 follows a complex path, turning one way and then another for no obvious reason.
Suppose we put Vehicle 1 in a pool of water. To you, it would seem somewhat restless, nervous. It would be frenetic in the day, somnolent at night. In fact, "you would say it is alive," writes Braitenberg, since nothing that's dead moves around quite like that.
This is one of Braitenberg's basic themes: that inferences we make from watching the behaviour of something -- like ascribing life to a vehicle -- are usually more complicated than the structure -- wheel, motor, sensor -- of the thing itself.
Vehicle 2 has two sensors and two wheels, and things get immediately more interesting. In one version, 2a, the left hand sensor connects to the left hand wheel, the right to the right. In 2b, the connections are switched, so that the left hand sensor connects to the right hand wheel and vice versa.
If we place a light bulb directly in front of Vehicle 2a, the little car speeds up and charges straight at the bulb. But if the bulb is even slightly to one side, let's say the right, the sensor on that side is more excited. This drives the right wheel faster, which turns the vehicle to the left: away from the bulb. 2b also speeds up and runs into a bulb placed directly in front of it. But if the bulb is to one side, this car turns toward the bulb, because the wheel on the opposite side turns faster. Eventually, inevitably, it hits the bulb.
The inferences? Both 2a and 2b "dislike" sources of light. But 2a tends to avoid them, turning away and searching for darker areas to escape to. 2a, you might think, is a coward. On the other hand, 2b is not scared of light sources. "It resolutely turns toward them and hits them with high velocity," writes Braitenberg, "as if it wanted to destroy them." Clearly then, 2b is aggressive. Not a coward.
Braitenberg describes ever-more complex vehicles which behave in ways that suggest to us, watching them, characteristics such as: love, a desire to explore, a system of values, knowledge, instincts, an ability to make decisions, a will, and more.
Ever more human characteristics, in fact.
This may make you wonder. Here we are, playing with a few wires, wheels and sensors, and we read these complex meanings into the behaviour of the toys we produce. "These vehicles," Braitenberg writes about Vehicle 4 and its variants, "are governed by instincts of various sorts, and, alas, we just don't know how Nature manages to embody instincts into a piece of brain."
"You forget, of course, that we have ourselves designed these vehicles."
The thought experiments suggested to Braitenberg a "law of uphill analysis and downhill invention." That is, it would be easy to make these little cars and have them perform their range of tricks: easy like going downhill. But it's more difficult -- like going uphill -- to analyse their behaviour and guess at their internal structure.
Analysis, says Braitenberg, is a much more difficult process than invention.
What's more, analysis tends to overestimate complexity. Considering the behaviour of a little car, we ascribe complex characteristics like love or cowardice to it. But those who invented it know that its behaviour is actually driven by simple gadgetry, no more.
That is: the simpler explanation is usually the correct one. An ancient truth, rising out of a thought experiment with cars. Let me push those things around a little more, won't you?