Introduction

User interfaces make measurements of the user and use those measurements to give the user control over some abstract domain. The sophistication of these measurements range from the trivial keyclick to the most advanced perceptual interface system. Once the measurements are acquired the system usually attempts to extract some set of features as the first step in a pattern recognition system that will convert those measurements into whatever domain of control the application provides. Those features are usually chosen for mathematical convenience or to satisfy an ad hoc notion of invariance. The expressivity of any such interface is limited by the user's ability to overcome the reality of their bodies and perform in this arbitrary feature space.

The fact that people are embodied places powerful constraints on their motion. An appropriate model of this embodiment allows a perceptual system to separate the necessary aspects of motion from the purposeful aspects of motion. The necessary aspects are a result of physics, are predictable. The purposeful aspects are the direct result of a person attempting to express themselves through the motion of their bodies. By taking this one thoughtful step closer to the original intentions of the user, we open the door to better interfaces. Understanding embodiment is the key to perceiving expressive motion.

Expressive power of an interface is hard to measure. Boredom can limit and color data collection. Subjective measures of efficacy are unsatisfying. Trivial contexts can hide the power of advanced interfaces. We are building a system for interface study around the the game Netrek. As a game it provides a built in metric for success: to win. It specifies a closed world that is simple enough to be tractable, not so trivial that context in meaningless. The need to communicate abstract concepts like strategy and coordination also provides opportunities to push the limits of what we expect from interfaces. We intend to use this test-bed to explore the above claims.

Context and coordination are very important in Netrek. There are programs, called robots, that know the basics of playing Netrek, but they do not, have a very good strategic engine or any ability to cooperate with other members of their team. Marcus Huber explored the idea of augmenting these robots to include cooperation with each other and found a significant advantage over uncoordinated robots[10]. We take a different approach. With a sufficiently sophisticated interface a human should be able to add strategy, coordination and structure to the robots' activities. This symbiosis between user and robots is called the Netrek Collective.

Chapter 2 explores some perceptual technology that we will use to build this interface. Specifically it explores the link between a perceptual system and the embodiment of the user being perceived. Chapter 3 provides more details about Netrek, a first implementation of the Netrek Collective. Finally, Section 3.3 details some directions for the Collective to grow.