A Braitenberg vehicle is an imaginary robot or creature used as the subject of a thought experiment to study embodied cognition. It was introduced by the Italian cyberneticist Valentino Braitenberg in his 1984 book Vehicles: Experiments in Synthetic Psychology. In the thought experiment, a vehicle equipped with sensors and actuators moves through a hypothetical environment, where orienting behaviors such as pursuit or avoidance are achieved by differential steering based on sensory input. A researcher may then analyze the vehicle's behavior to better understand how it relates to the wiring. Braitenberg presented fourteen vehicle types of increasing complexity, from simple creatures that demonstrate phototaxis to complex creatures that show behavior suggestive of psychological phenomena, such the formation of concepts and generation of ideas. The thought experiment has been used in neuroscience, artificial life, and robotics, in simulated and real environments.
Overview A Braitenberg vehicle is an autonomous agent that moves through its environment based on sensory input. Its locomotion behavior is determined by the pattern of wiring that connects its sensors, such as light or odor sensors, to the actuators, often imagined or realized as wheels. In an environment with multiple stimuli, a vehicle can exhibit complex and dynamic behavior. Depending on the connections between sensors and actuators, it might move close to a source, but not touch it, run away very fast, or make circles or figures-of-eight around a point. Vehicles can be considered singly in their environment, or as part of a multi-agent system.
Uses
Braitenberg vehicles have been incorporated into a variety of fields of research, such as robotics, artificial life, and neuroscience. Robotics researchers have used the idea to develop robots that can autonomously orient toward or away from stimuli such as odor and sound, such as in path planning. In neuroscience, vehicles have been used to better understand how animals navigate, including chemotaxis in fruit flies and cockroaches, and phonotaxis in lizards, salamanders, and bats, and have been compared to the nervous systems of ciliated larvae. Vehicles have also been used as a teaching tool, and in simulation games. Artificial life researcher Seth Bullock argued that Braitenberg's approach, starting with construction and experimentation rather than analysis, can make understanding behavior easier: "Tinkering with the systems in order to achieve some interesting behaviour is far easier than analysing these systems to determine why a particular configuration of sensors, wires, and motors gives rise to the particular behaviour that it does." But he also noted that an intuitive simulation model may introduce its own analytical requirements. Cognitive scientist and philosopher Daniel Dennett described Braitenberg's early vehicle types as "comically simple", and argued that adding to the vehicle and elaborating on its design is "a process that fruitfully echoes evolution by natural selection and yields many insights into the historical and structural constraints on design-development in living things." Cybernetician Michael A. Arbib called Braitenberg's process of tinkering "ad hoc evolution", to distinguish it from evolution by natural selection, genetic algorithms, and conceptual neural evolution.
History The ideas presented in Vehicles had their origins in previous work. As a neuroanatomist, Braitenberg studied the cerebellum to understand its role in complex timing behaviors such as humans playing music. He took a particular interest in decussation, or the crossing of nerve fibers, as it relates to taxis and kinesis behaviors. Early ideas were expressed in a 1965 paper almost 20 years prior to the book, where he speculated that decussation in vertebrate brains may be due to an ancestor that used olfactory taxes. He also focused on symmetries in neuroanatomy, including in visual cortex and rat barrel cortex. In a 1977 paper, Braitenberg credited German mathematician Hermann Weyl's 1952 book Symmetry as influential in forming his ideas.
Original formulations
Braitenberg outlined 14 types of vehicles, in increasing complexity, and deliberately used cognitive and psychological terms when describing their behaviors. For example, Vehicle 1 illustrates a 1-dimensional creature that responds to a simple stimulus by moving forward, akin to kinesis. Vehicles 2a, 2b, 3a, and 3b exemplify the 4 main ways vehicles navigate their environment, usually the basis for behavioral observation and analysis. These vehicle types introduce taxis. Subsequent vehicles elaborate on these basic principles, including hardware upgrades and more complex connections between sensors and actuators.
Vehicle 1
In Braitenberg's simplest configuration, a temperature sensor is connected directly to the vehicle's only wheel. Any temperature above absolute zero activates the sensor, which in turn activates the wheel, pushing the vehicle forward. As the temperature increases, so does the wheel's speed. The resulting behavior of this vehicle is that it moves along a straight line. However, asymmetrical frictional forces can cause the vehicle to deviate from its straight line motion in unpredictable ways akin to Brownian motion. To a human observer, this creature might appear 'alive' and 'restless', never stopping in its movement. The low speed in regions of low temperature might be interpreted as a preference for cold areas.
Vehicles 2 and 3
More complex vehicle types include two sensors and two wheels in a body with bilateral symmetry, capable of taxis via differential steering. Braitenberg imagined a vehicle that has left and right sensors at the front of the body, and left and right wheels at the rear. This design presents four possible wiring configurations depending on whether the wires are connected ipsilaterally (same side) or contralaterally (crossed), and whether the connections are excitatory (increase wheel activation) or inhibitory (decrease wheel activation). In this class of vehicles, differential steering plays the key role. When the intensity of the stimulus is greater in one sensor than in the other, one wheel will be driven at a higher speed than the other, causing the vehicle to turn. The 4 wiring configurations were named by Braitenberg to capture the psychology the vehicles appeared to him to be demonstrating: fear, aggression, love, and exploration.
Type 2a: Fear
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