Thought experiment by neuroscientist Valentino Braitenberg.
Vehicles: Experiments in Synthetic Psychology, MIT Press, 1984
14 types of vehicles of increasing complexity.
Vehicle 1: single sensor-motor coupling
Sensor measures concentration of X (temperature, light, chemical gradient, food, noise, etc.)
Vehicle moves forward in response to amount of X
If X is temperature, vehicle will move fast in hot regions and slow in cold regions
Appears to "like" cold regions and "dislike" hot regions
Friction in environment results in more complicated behavior
Vehicle 2a, 2b: two sensors, positive connections
Each motor stimulated by one of the sensors
Vehicle 2a is a "coward" (it avoids X)
Vehicle 2b is "aggressive" (it approaches X and speeds up)
Vehicle 3a, 3b: two sensors, negative connections
Each motor inhibited by one of the sensors
Vehicle 3a "loves" X (it turns toward X and stays close by)
Vehicle 3b likes X too but keeps an eye out for other sources (it gradually moves away from X)
Vehicle 3c: multiple sensors and connections
Several types of sensors, tuned to different aspects of environment
Mixture of excitatory and inhibitory connections
Now we have really interesting behavior:
Vehicle 3c has a system of "values"
It "knows" what it likes and dislikes
Vehicle 4: non-linear sensory response curves
response to X is no longer simply linear
response may be continuous, discontinuous, or a combination of both
Vehicle 4 appears to "pondor" over its decisions (discontinuous thresholds)
Behavior is now even more interesting:
We might be tempted to attribute "free will" to the vehicle
Vehicle 5: threshold logic units, neural networks
Vehicle 6: evolution
Vehicles 7-14: learning, more sophisticated cognitive abilities
"Law of uphill analysis and downhill invention"
Easy to implement vehicles 1-5 as mobile robots.