Models of Purposeful Motion

Figure 2.3: Modeling tracking data of circular hand motion. Passive physics alone leaves significant structure in the innovations process. Top Left: Smoothing the innovations reveals unexplained structure. Top Right: Plotting the Innovations along the path makes the purposeful aspect of the action clear. Bottom: In this example, using a learned control model to improve predictions leaves only white process noise in the innovations process. The smoothed innovations stay near zero.

$\parbox{0.80in}{Physics-only Model \\ }$ [height=40mm]figs/circle-innovations-A [height=40mm]figs/circle-innovations-B

$\parbox{0.80in}{Physics + \\ Behavior \\ Model \\ }$ [height=40mm]figs/circle-controlled-A [height=40mm]figs/circle-controlled-B

Observations of the human body reveal an interplay between the passive evolution of a physical system (the human body) and the influences of a an active, complex controller (the nervous system). Section 2.2.1 explains how, with a bit of work, it is possible to model the physical aspects of the system. However, it is very difficult to explicitly model the human nervous and muscular systems, so the approach of using observed data to estimate probability distributions over control space is very appealing.