Chapter 4: The Simple Unstable Vehicle: a manual control task

The early studies of the last chapter gave conclusions which usefully bounded the desired area of study on two sides. On the one hand, the study of a real-life task seemed to be so complex that it prevented effective progress towards the fundamental objective: the modelling of the cognition involved in complex tasks in terms at least of the representations used. A more restricted and well-defined task was needed. On the other hand, machine learning alone did not promise to reveal human representations or human rules: there being too large a space of possible representations, a plausible qualitative guess was not good enough. It was clear that the research needed to include the study of human control. The encouraging aspect of these conclusions was that there was plenty of scope between these two extremes, and that the extremes had at least delimited the areas of study that were more likely to be fruitful.

Following on from the previous chapter (§ 3.2), an immediately apparent idea was to study human control of an actual, or simulated, pole-balancing task. The objection to this was that, even if balancing a broom on a finger-tip was a practiced skill in many people, balancing the pole-and-cart system with bang-bang control is not a skill which many people have picked up in their normal course of life. Therefore this would be largely a learning situation. However, there is a common system with similar characteristics that many people have experience on: the bicycle.

Though most adults can ride a bicycle with great skill and coordination, there are no reports of people giving a full account of the content of that skill. On the contrary, in the author's experience of asking people, it is normal to have misconceptions about how bicycle riding is performed. Certainly many authors have used it as an archetypal example of a skill that is not communicated by words.

The technical difficulties of studying real bicycle control put it out of experimental reach of a project such as the current one, perhaps further out of reach than the study of real maritime collision avoidance, discussed above (§ 3.1). The alternative was to create a bicycle-like simulation, using the computer equipment available. The author had a reasonable understanding of the fundamental physics involved in bicycle dynamics, but did not feel confident to start modelling the finer points such as the gyroscopic effects of the wheels. To distinguish this model from a high-fidelity mathematical model, it was decided to call it the Simple Unstable Vehicle, or SUV for short.

There were two parts to this study of the SUV. In the first, a mathematical model was implemented, which could test the performance of different hand-written control rules, and the results were displayed graphically. In the second, a handlebar interface was constructed to enable a human subject to control the simulation interactively, while watching a display showing the view from riding the SUV.