In effect, this list, along with other items that ought to have been included in it, is the working definition of AT.

AT is all of these and all other systems and devices that support and enhance activity in similar ways. One can imagine an enormous table with a long list of impairments and disabilities down one side and an infinite list of life activities and environments across the top. AT, at least conceptually, can be invented for every cell in this table, i.e., for every situation in which a change in ability or capacity or function has rendered independent performance more difficult or impossible.

A quick review of the list on the previous page shows that some AT is intended to enable a whole category of activities by fundamentally altering the user, e.g. an EMG-driven arm prosthesis; while other AT devices, e.g. a home ECU, offers limited purpose access to a single or small number of functions. If one views a disabling condition as imposing a wall between the individual and much of the world, some AT allows the individual to leap over the wall, while other AT provides a door through the wall into a particular room on the other side.