How can people with disabilities navigate in virtual reality with an input device they can use?

Three dimensional computer graphics are common nowadays for games and are beginning to be used in other applications as well, such as for displaying information, navigation on the internet and as an interface to programs. As always, though, a new computer interface form such as this excludes a number of potential users. In this case, those people who are not able to see the graphics and others who are physically unable to manage the input devices necessary to control a viewpoint and objects in three dimensional movement.