As computer systems become more powerful and complex, efforts to make computer interfaces more simple and natural become increasingly important. Natural interfaces should be designed to facilitate communication in ways people are already accustomed to using. Such interfaces should allow users to concentrate on the tasks they are trying to accomplish, not worry about what they must do to control the interface.
In this paper, we begin by discussing what input modalities humans are comfortable using when interacting with computers, and how these modalities should best be combined in order to produce natural interfaces. In section three, we present a prototype map-based application for the travel planning domain which uses a synergistic combination of several input modalities. Section four describes the agent-based approach we used to implement the application and the work on which it is based. In section five, we summarize our conclusions and future directions.