William Warren

Department of Cognitive & Linguistic Sciences

Brown University

The dynamics of perception and action: of bouncing babies and legged locomotion.

Where does the organization in behavior come from? I will develop the view that stable behavior emerges from the interaction between agent and environment, exploiting physical and informational constraints. This interaction can be formalized as a nonlinear dynamical system, called the behavioral dynamics. Two case studies illustrate this approach.

First, how do six-month olds learn to bounce in a "jolly jumper"? A longitudinal study reveals that infants suddenly discover the solution of driving the system at its natural frequency. This can be modeled as a forced mass-spring system whose parameters are specified by perceptual information.

Second, how do adults visually guide locomotion through a complex, changing environment? Locomotor behavior can be decomposed into four basic components:  (a) steering toward a stationary goal, (b) avoiding a stationary obstacle, (c) intercepting a moving target, and (d) avoiding a moving obstacle. We use a virtual environment to study each behavior and model it as a dynamical system.  By combining these components, we can predict locomotor paths in more complex environments.

Organized behavior can thus be understood as emerging on-line from the interaction between a structured environment and an agent with simple control laws, making explicit planning unnecessary.