To react or not to react? Intrinsic stochasticity of human control in virtual stick balancing

Abstract

Understanding how humans control unstable systems is central to many research problems, with applications ranging from quiet standing to aircraft landing. Increasingly much evidence appears in favor of event-driven control hypothesis: human operators only start actively controlling the system when the discrepancy between the current and desired system states becomes large enough. The event-driven models based on the concept of threshold can explain many features of the experimentally observed dynamics. However, much still remains unclear about the dynamics of human-controlled systems, which likely indicates that humans employ more intricate control mechanisms. The present paper argues that control activation in humans may be not threshold-driven, but instead intrinsically stochastic, noise-driven. Specifically, we suggest that control activation stems from stochastic interplay between the operator's need to keep the controlled system near the goal state on one hand and the tendency to postpone interrupting the system dynamics on the other hand. We propose a model capturing this interplay and show that it matches the experimental data on human balancing of virtual overdamped stick. Our results illuminate that the noise-driven activation mechanism plays a crucial role at least in the considered task, and, hypothetically, in a broad range of human-controlled processes.

Extended phase space description of human-controlled systems dynamics

“…However, the operator neglecting small velocity deviations (v th of order unity) can handle maintaining the bounded motion of the system, even though by cost of increased motion amplitude. This situation corresponds well to the experimental findings on human control of in-verted pendulum, where the continuous control is less efficient in comparing to the discontinuous, or intermittent control [14,29]. Particularly, in balancing an inverted pendulum human operators who ignore small deviations from the vertical position perform better than the operators trying to react to every detectable deviation [29].…”

“…This situation corresponds well to the experimental findings on human control of in-verted pendulum, where the continuous control is less efficient in comparing to the discontinuous, or intermittent control [14,29]. Particularly, in balancing an inverted pendulum human operators who ignore small deviations from the vertical position perform better than the operators trying to react to every detectable deviation [29]. Finally, we make some remarks on the cases of ∆ v = 1 and ∆ a = 1.…”