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 ;hysical 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 natrual 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.

The Dynamics of Perception and Action