Like I imagine every red-blooded male kid did, I loved toys with four wheels. Like a sleek Alfa Carabo my uncle gave me. Only much later did I realize I should have preserved it: the real car itself never saw production.
No sleek Carabos, Braitenberg’s vehicles are instead basic affairs.
They have sensors, wheels driven by motors and no more. The sensor responds to light by sending electrical impulses to the motor, which turns and propels the vehicle.
His simplest vehicle, Vehicle 1, has one sensor connected to one motor that drives one wheel. Place it in front of a light bulb and the motor whirrs into action, thrusting Vehicle 1 in whichever direction it’s pointing. The stronger the light source, the faster the motor turns.
It speeds up where there’s plenty of light, slows where it’s dark.
In outer space, Vehicle 1 would move in a straight line, its speed changing as it passes light sources. But on the earth, friction causes it to change direction in unpredictable ways. (Think of giving a model car a push: does it ever follow a perfectly straight line?) So its speed varies with the light, its direction varies with friction, and Vehicle 1 follows an intricate path all its own, turning this way and that with no obvious pattern. It races about frantically in the day; it seems sleepy at night.
To an onlooker, it would seem almost restless, strangely nervous. “You would say it is alive,” wrote Braitenberg, since nothing that’s dead moves like that.
Yet, of course, Vehicle 1 is just a car. Yet how easily we attribute character to it. Yet wait.
Vehicle 2 comes in two varieties, both with two sensors and two wheels. In 2A, the left-hand sensor connects to the left-hand wheel, the right to the right. In 2B, the connections cross: the left sensor connects to the right wheel and vice versa.
What happens when we place a light bulb directly in front of Vehicle 2A? The sensors pick up light in equal strengths, so both motors rotate at the same speed. As the car approaches the bulb and is bathed in ever-brighter light, its speed steadily increases. That is, 2A charges straight at the bulb, accelerating as it goes. But if the bulb is even slightly to the left, say, the sensor on the left gets more excited. This drives the left wheel faster, turning 2A away from the bulb.
2B also charges into a bulb that’s placed directly in front. But if the bulb is to the left instead, this car’s right wheel rotates faster. So 2B veers towards the bulb, accelerating all the time, and eventually crashes into it.
Braitenberg characterized both 2A and 2B as light source haters. But how differently they show their hatred. 2A tries to avoid the bulb, slinking into the shadows in search of shelter. Call it a coward. 2B is the opposite. Not frightened by light, it instead becomes aggressive. “It resolutely turns toward (light sources)”, wrote Braitenberg, “and hits them with high velocity, as if it wanted to destroy them”.
You get the idea. In his book, Braitenberg described ever more complex vehicles which suggested to him, watching them move, characteristics such as love, a desire to explore, knowledge, a system of values, a will, instincts, an ability to make decisions and more. Characteristics, in fact, such as a human might exhibit.
Makes you wonder. We read these elaborate meanings into the behaviour of things we build; things, remember, that Braitenberg merely thought up for his book. Check what he wrote about Vehicle 4 and its variants:
“These vehicles 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.”
Yet of course, these are just concoctions of wire, wheels and sensors.
“You forget,” wrote Braitenberg, “that we have ourselves designed these vehicles.”
His experiments suggested to Braitenberg a “law of uphill analysis and downhill invention”. That is, it’s easy to invent these vehicles and have them perform their charming tricks: easy like going downhill. But if you analyse their behaviour and try to guess at their internal structure, that’s far more difficult: like going uphill.
What’s more, analysis overestimates complexity. We ascribe complex characteristics such as love or cowardice to these cars. But their behaviour is really explained fully by what their sensors are doing in concert with the wheels. Simple.
A YouTube video has an Alfa Carabo racing a Chevy Camaro. They both go downhill. The Carabo wins by a whisker. I think the Camaro was lazy.
Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. A Matter of Numbers will explore the joy of mathematics, with occasional forays into other sciences. Comments are welcome at dilip@livemint.com
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