A Braitenberg vehicle is a concept conceived in a thought experiment by the Italian-Austrian cyberneticistValentino Braitenberg. The book models the animal world in a minimalistic and constructive way, from simple reactive behaviours through the simplest vehicles, to the formation of concepts, spatial behaviour, and generation of ideas. For the simplest vehicles, the motion of the vehicle is directly controlled by some sensors. Yet the resulting behaviour may appear complex or even intelligent.
Mechanism
A Braitenberg vehicle is an agent that can autonomously move around based on its sensor inputs. It has primitive sensors that measure some stimulus at a point, and wheels that function as actuators or effectors. In the simplest configuration, a sensor is directly connected to an effector, so that a sensed signal immediately produces a movement of the wheel. Depending on how sensors and wheels are connected, the vehicle exhibits different behaviors. This means that, depending on the sensor-motor wiring, it appears to strive to achieve certain situations and to avoid others, changing course when the situation changes. The connections between sensors and actuators for the simplest vehicles can be ipsilateral or contralateral, and excitatory or inhibitory, producing four combinations with different behaviours named fear, aggression, liking, and love. These correspond to biological positive and negative taxes present in many animals species.
Examples
The following examples are some of Braitenberg's simplest vehicles.
Vehicle 1 - Getting Around
The first vehicle has one sensor that directly stimulates its single wheel in a directly proportional way. The vehicle moves ideally in one dimension only and can stand still or move forward at varying speed depending on the sensed temperature. When forces like asymmetric friction come into play, the vehicle could deviate from its straight line motion in unpredictable ways akin to Brownian motion. This behavior might be understood by a human observer as a creature that is 'alive' like an insect and 'restless', never stopping in its movement. The low velocity in regions of low temperature might be interpreted as a preference for cold areas.
Vehicle 2a
A slightly more complex agent has two symmetric sensors each stimulating a wheel on the same side of the body. This vehicle represents a model of negative animal tropotaxis. It obeys the following rule:
More light right → right wheel turns faster → turns towards the left, away from the light.
This is more efficient as a behavior to escape from the light source, since the creature can move in different directions, and tends to orient towards the direction from which least light comes. In another variation, the connections are negative or inhibitory: more light → slower movement. In this case, the agents move away from the dark and towards the light.
Vehicle 2b
The agent has the same two symmetric sensors, but each one stimulating a wheel on the other side of the body. It obeys the following rule:
More light left → right wheel turns faster → turns towards the left, closer to the light.
As a result, the robot follows the light; it moves to be closer to the light.
Behavior
In a complex environment with several sources of stimulus, Braitenberg vehicles will exhibit complex and dynamic behavior. Depending on the connections between sensors and actuators, a Braitenberg vehicle might move close to a source, but not touch it, run away very fast, or describe circles or figures-of-eight around a point. This behavior is undoubtedly goal-directed, flexible and adaptive, and might even appear to be intelligent, the way some minimal intelligence is attributed to a cockroach. Yet, the functioning of the agent is purely mechanical, without any information processing or other apparently cognitive processes. Often, BEAM robotics implements these sorts of behaviors.
