Skilled motor control of an inverted pendulum implies low entropy of states but high entropy of actions

The mastery of skills, such as balancing an inverted pendulum, implies a very accurate control of movements to achieve the task goals. Traditional accounts of skilled action control that focus on either routinization or perceptual control make opposite predictions about the ways we achieve mastery. The notion of routinization emphasizes the decrease of the variance of our actions, whereas the notion of perceptual control emphasizes the decrease of the variance of the states we visit, but not of the actions we execute. Here, we studied how participants managed control tasks of varying levels of difficulty, which consisted of controlling inverted pendulums of different lengths. We used information-theoretic measures to compare the predictions of alternative accounts that focus on routinization and perceptual control, respectively. Our results indicate that the successful performance of the control task strongly correlates with the decrease of state variability and the increase of action variability. As postulated by perceptual control theory, the mastery of skilled pendulum control consists in achieving stable control of goals by flexible means.Author summary: What characterises skilled behaviour? When one observes capable tennis players or other masters of their craft, their performance appears effortless, their behaviours purposeful and stable. This has been suggested in some traditional accounts to imply that mastery of a task is linked to highly routinised behaviours; such behaviours would concentrate on well-rehearsed routes. Others have proposed instead that mastery consists in keeping the states well confined during a behaviour; where necessary, actions would vary strongly to achieve that. Which of these is the case? Here, we undertake a study where participants have the task to balance an inverted pole. The length of the pole can be varied, which permitted us to control the difficulty of the task. Using methods from information theory, we set out to answer above question in the case of pole balancing control. We found that successful balancing correlates strongly with focused, well controlled states, but at the cost of having highly varying actions. In other words, a potentially wide choice of actions serves to maintain the system tightly in preferred states. According to these results, mastery (in this task) is not about choosing the same actions repeatably, but about reliably achieving the same outcomes.