Page 470 - Biomedical Engineering and Design Handbook Volume 2, Applications

448 REHABILITATION ENGINEERING AND PROSTHETICS DESIGN

for people who have low vision. Some commonly used operating systems have built-in adaptations.
∗
The Macintosh operating system includes a screen magnification program called Zoom. This program
allows for magnification from 2 to 20 times and has fast and easy text-handling and graphics capabilities.
More information is available on the Apple accessibility Web site http://www.apple.com/accessibility.
Magnifier is a minimal function screen magnification program included in Windows. Magnifier
†
displays an enlarged portion of the screen (in Windows XP, from 2 to 9 times magnification; in
Windows Vista, from 2 to 16 times) and uses a part-screen approach and has three focus options:
mouse cursor, keyboard entry location, and text editing. Accessibility Options for Windows XP, Ease
of Access for Windows Vista, and Universal Access for Macintosh contain other adaptations such as
color contrast, cursor size, and icon size.
Software programs that are purchased separately rather than being built-in offer wider ranges of
magnification and have more features than built-in screen magnifiers. Hardware and software combi-
nations have other features such as multiple enlarged windows, smoother scrolling, and a wider range
of magnification. Cook and Polgar (2008) and Lazzaro (1999) describe commercial approaches to
screen magnification utilities. Most of these approaches also allow adjustment of background and
foreground colors to address difficulties with contrast.

Alternatives to Visual Input for Individuals Who Are Blind. For individuals who are blind, com-
puter outputs must be provided in either auditory or tactile form or both. Auditory output is typically
provided through systems that use voice synthesis, and tactile output is in Braille. These adaptations
are generally referred to as screen readers. In its accessibility options, Windows TM includes a basic
function screen reader utility, Narrator, and a program called Toggle Keys that generates a sound
when CAPS LOCK, NUM LOCK, or SCROLL LOCK key is pressed.
Macros in screen reader programs are useful in moving between windows or locating key areas
(e.g., a dialog box or a window requiring input from the user). Screen readers are ideally suited for
applications that consist of text only.
GUI design uses an approach that creates many options for the portrayal of graphic information
to video display control. Since each character or other graphical figure is created as a combination
of dots, letters may be of any size or shape or color, and many different graphical symbols can be
created. This is very useful to sighted computer users because they can rely on the use of “visual
metaphors” (Boyd et al., 1990) to control a program. Visual metaphors use familiar objects to
represent computer actions. For example, a trash can may be used for files that are to be deleted, and
a file cabinet may represent a disk drive. The graphical labels used to portray these functions are
referred to as icons. Screen location is important in using a GUI, and this information is not easily
conveyed via alternative means such as screen readers. Visual information is spatially organized and
auditory information (including speech) is temporal (time based). It is difficult to convey screen
location of a pointer by speech alone. An exception to this is screen locations that never change
(e.g., the edges of the screen such as “right border,” “top of screen”). Another major problem is that
mouse pointer location on the screen is relative, and the only information available is the direction
of the movement and how far the mouse has moved. One approach to this problem is the Microsoft
‡
Screen Access Model. This is a set of technologies designed to facilitate the development of screen
readers and other accessibility utilities for Windows TM that provide alternative ways to store and
access information about the contents of the computer screen. The Screen Access Model also
includes software driver interfaces that provide a standard mechanism for accessibility utilities to send
information to speech devices or refreshable Braille displays. GUI access also requires capability for
locating open windows, monitoring them for changes, and outputting information to the user if
changes occur. Screen reader programs also provide assistance in this “navigation” function by using
keyboard commands such as movement to a particular point in the text, finding the mouse cursor
position, providing a spoken description of an on-screen graphic or special function key, or access-
ing help information. Screen readers also monitor the screen and take action when a particular block

∗ Macintosh Operating System, Apple Computer, Cupertino, Calif., www.apple.com/accessibility.
† www.microsoft.com/enable/default.aspx.
‡ www.microsoft.com/enable/products/microsoft.