A simple, abstract model for rhythmic locomotion is a stable periodic orbit of a vector field. Stability often requires feedback and control. This talk will discuss how an organism might estimate parameters in a model controller. Noise in the system is inevitable. The resulting fluctuations give information useful for estimating the parameters. However, the time required may be implausibly slow in systems with Gaussian noise, prompting the search for alternative models. What are experiments that might give further insight into these issues?