Human Machine Interaction
The sensory impairment that has attracted the most attention from researchers, perhaps because it is potentially also one of the most debilitating as far as interaction is concerned, is visual impairment. Visual disabilities range from impaired visual acuity, often resulting from aging; decreased sensitivity to a specific color or colors; partial blindness, or total blindness. Moderately impaired vision may simply require the availability of larger fonts or restrictions in the use of colors. Severe impairments, such as blindness, may require compatibility with speech or Braille utilities. The rise in the use of graphical interfaces reduces the possibilities for visually impaired users. In text-based interaction, screen readers using synthesized speech or braille output devices provided complete access to computers: input relied on touch-typing, with these mechanisms providing the output. However, today the standard interface is graphical. Screen readers and braille output are far more restricted in interpreting the graphical interface, meaning that access to computers, and therefore work involving computers, has been reduced rather than expanded for visually impaired people. There are two key approaches to extending access: the use of sound and the use of touch.
The best accessibility standards that should be applied in the design of a website for visually impaired people can be summarized as follows:
For people who cannot use a screen’s visual content, a screen-review utility will be necessary.
- These utilities, also called screen-reader programs or speech access utilities take the displayed information being focused on and direct it through another medium like speech. Screen readers like Freedom Scientifics’ JAWS allow users with visual impairments to productively navigate between windows, select applications, browse graphical interfaces, and of course read text.
- Alternate media include synthesized speech and refreshable Braille displays. Outspoken is a Macintosh application that uses synthetic speech to make other Macintosh applications available to visually impaired users.
- Screen enlargement utilities enable the user to enlarge a portion of the screen, the monitor becoming a viewport that displays only a section of an enlarged display. These programs also referred to as screen magnification utilities or large-print programs, track the user’s use of a keyboard or mouse, moving the viewport to different areas of the screen as the user navigates within it.
- Meaningful, specific, and unique screen and window titles will assist the user in differentiating between these, especially when using a screen-review utility. When using a reader, content must be addressed separately, so it will not be available with the title to aid in comprehension of what is presented.
- Provide associated labels or captions for all controls, objects, icons, and graphics, since all screen information must be presented as text by a screen reviewer. These labels must also be located in close proximity to the screen elements they refer to. A screen reviewer will relate the label to its associated screen element by its physical proximity, if it is not related programmatically. In rare situations, where the caption may be visually distracting (display-only data on inquiry screens, for example), provide a label but do not make it visible. Graphical menu choices, such as illustrated colors, shades, and patterns, must also possess textual labels.
- Also provide a textual summary for each statistical graphic. Statistical graphics are images containing detailed information and, because of their graphic nature, their contents cannot be conveyed by a screen reader. The textual summary should include all information available to a sighted user.
- Support screen element scalability, the presentation of larger text and graphics for people with only slight or moderate vision impairment. Also consider providing a “Zoom” command that scales the information displayed within a window.
- Support system settings for high contrast for all user interface controls and client area content. Users with visual impairments require a high contrast between foreground and background elements for best text legibility. Poor contrasts may result severely degraded legibility because the background may “bleed” into the foreground. When a “high contrast” setting is established, hide any images drawn behind text (watermarks, logos, patterns, and so on) to maintain screen information legibility.
- Monochrome versions of graphics and icons can also be presented using an appropriate foreground color for the displayed background color. In general, use black text on a white background to achieve the best foreground-background contrast. While some softer colors may be more attractive to look at, black on white always yields the best legibility.
- Finally, avoid displaying or hiding information based on the movement of the pointer, unless it is part of the standard interface (a ToolTip, for example). These techniques may not be available to screen-review utilities. If these techniques are used, however, allow them to be turned on or off if a screen-review utility is used.
- Provide a thorough and complete keyboard interface.
- Blind users cannot use a mouse to navigate because the pointer’s location is unknown.
- All mouse actions, therefore, must be available through the keyboard using keyboard equivalents and keyboard accelerators.
- A logical order of screen element navigation is also a requirement for blind users. While this principle is standard for all screen users, a failure to adhere to it can be especially confusing for the blind because, when using a screen-review utility, they must navigate a screen sequentially in the predetermined navigation order. Their ability to scan the entire contents of a control or screen to establish context is simply not possible.
- Color must always be used as a supplemental or enhancing design characteristic.
- Users with a color-viewing deficiency may not be able to discriminate certain colors, and, consequently, they may be unable to understand that an action is required if the action is based upon an element’s color alone.
- Provide a variety of color selections capable of producing a range of contrast levels.
- Create these combinations based on the system colors for window components.
- Never define and use specific colors.
- With a selection variety, the user may then customize the interface, choosing the best combination for his or her visual needs.
- Ensure that all images have meaningful alternative text. This alternative text is read out by screen reader so that the user understands what is being shown on the screen. Providing alternatives to text that can be changed into other forms such as large print, or maybe a more simplified form of the language.