A screen-reader is a computer application designed to provide spoken feedback to a visually impaired user. Screen-readers have been available since the mid-80's. During the 80's, such applications relied on the character representation of the contents of the screen to produce the spoken feedback. The advent of bitmap displays led to a complete breakdown of this approach, since the contents of the screen were now light and dark pixels. A significant amount of research and development has been carried out to overcome this problem and provide speech-access to the Graphical User Interface (GUI).
The best and perhaps the most complete speech access system to the GUI is Screenreader/2 (ScreenReader For OS/2) developed by Dr. Jim Thatcher at the IBM Watson Research Center [Tha94]. This package provides robust spoken access to applications under the OS2 Presentation Manager and Windows 3.1. Commercial packages for Microsoft Windows 3.1 provide varying levels of spoken access to the GUI. The Mercator project [Myn94][MW94][WKES94][ME92] has focused on providing spoken access to the X-Windows system.
A common feature of traditional DOS-based screen-readers and speech access packages to the GUI is their attempt to convey the contents of the visual display via speech. In fact, a significant amount of the development effort required to design speech-access packages to the GUI has concentrated on building up robust off-screen models -a data structure that represents the contents of the GUI's visual display. Construction of such an off-screen model helps screen-readers regain the ground they lost due to the advent of graphical displays. However, the nature of spoken feedback provided does not change.