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Visual displays

With respect to ICT systems, visual displays include any information that is presented electronically. Examples include screens on ATMs, ticket vending machines and information kiosks, and information displays in stations and airports.

Visual displays can pose problems for both disabled and elderly people. However, these same problems can also be encountered by users with minor visual problems. For example, people who wear bifocals find it difficult to read the screen of most public access terminals, since the screen may not be at a suitable distance for either the near or far segments of their spectacles. Also, many people leave their spectacles in the car or do not wear them in public.

So, the number of people who have problems in reading the screen is much more than the 1.9% of the population considered to be blind or to have low vision.

Format of displayed text
Good standards of legibility helps all users, but for people with low vision the issue is crucial for reading text. Text should be displayed using high contrast colour combinations. A clear open font type should be used.

Patterned backgrounds or an image in the background of text reduces the legibility of the text.

Flashing text attracts attention but can be hard to read. If this is used, the text could flash a few times and then stop.

Scrolling or moving text also creates significant problems for people with low vision, as the reader's eyes have to move at the same time as focussing on the text. On an information board, showing blocks of text for a few seconds at a time would be easier to read than continuously scrolling the text. If all of the text does not fit on the screen or display in one showing, then the text could be split into consecutive blocks, each revealed for a few seconds. If the text requires many blocks, providing "page" numbers (e.g. 1/3, 2/3 and 3/3) would be helpful, so the reader knows how much text will appear.

Terminals which offer a full display of text on a visual display unit should allow adjustment of the size of the characters. The characters must also be of good proportions with clear character shapes. There must also be a strong contrast between the characters and the background.

For some visual impairments it is also helpful to be able to reverse the text from dark on a light background to light characters on a dark background.

There should be no noticeable flicker on the screen. Add-on assistive devices should not cause the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

Navigating the machine
On most terminals the visual instructions on the screen are the main guide for the user. Instructions should be clear and concise and, if possible, should appear one instruction at a time.

It might be helpful to indicate the number of tasks or "pages" that the transaction will entail. For example:

Instruction 1/6: Insert card
Instruction 2/6: Enter PIN number

This way the user will have a rough estimate of how much longer the whole process will take.

Displays must be compatible with how people expect the information to be presented so they can control its actions. The orientation should be compatible with the real world to prevent confusion. The moving components should be compatible with the direction of movement that occurs naturally e.g. 'up' results in an upward movement and increase in numerical value. Feedback would allow the person to check that their intention has been carried out.

The choice of pictograms and icons should be considered carefully to ensure that they are meaningful to the target audience and are visually distinctive.

Finding a pointer or cursor on a screen can be difficult for people with low vision. So a means of drawing attention to this can be helpful. A familiar way of doing so on PCs is the option to "Show location of pointer when I press the Ctrl key", which reveals the location of the cursor by means of a flashing circle.

Speech Output
Speech output can help make instructions easier to understand, by talking the user through the process. Spoken instructions should be short and concise, as an excessive amount of speech output might be distracting.

Speech output should not be the only means of accessing the instructions, since users with a hearing impairment might not be able to rely on this alone. Instructions presented in a combination of formats, for example both audio and text, will be accessible to a larger number of users.

A 'repeat last instruction' option would be useful if the user misses an instruction.

Speech output that informs the user, for example, "Please wait while your tickets are being printed" can reassure the user that the machine is not awaiting their input, if there is a delay in any process.

Providing as much information as possible
If tickets or an information sheet are being printed, it is useful to tell the user the number of pages that is going to be printed. For example, when a train ticket is bought there may be three tickets printed: one for the outward journey, one for the return journey and a receipt. If it is not obvious that the machine is still completing the transaction, the user might walk away too early.

Use of colour
Colour stands out and so it is often used to highlight or code information. No more than five colours should be used in any display. Colour alone should not be used to explain information. Providing numeric coding beside each option or grouping related options together might help to alleviate this problem.

The most common forms of colour blindness are inherited and are associated with the inability to discriminate red and green wavelengths. These defects are described as 'sex-linked', as the gene occurs on the X-chromosome. Males only have one X-chromosome, whereas females have two. As a result of this colour blindness is more prevalent in males (c. 8.0%), than it is in females (c. 0.5%). Total colour blindness is extremely rare.

Even for users who do not have colour blindness, excessive use of colours can be distracting. Also, since some colour combinations have better contrast, the use of too many colours might increase the chance of including a low contrast combination in the display.

Bright colours can produce glare, which might distract the user and cause the eyes to become tired.

Screen position
Sunlight can degrade the visibility of the display for all users. The screen should be shielded from direct or reflected sunlight or other bright light sources to prevent glare.

The display should be visible from the eye level of a person sitting in a wheelchair.

People cope with glare by, for example, squinting, closing their eyes or moving their head to an extreme angle. People with low vision should not be prevented from getting their faces close to the screen.

Filters (such as a Venetian blind effect), can be incorporated into a screen to reduce glare and also to prevent passers by from reading private information off the screen. However, limiting the angles at which the screen can be read can prevent very tall or very short users (including those in a wheelchair), from seeing the screen clearly.

Illustration of the displayed options lined up with the function keysParallax problems
The conflicting requirements of tall pedestrian users and small wheelchair users can lead to a significant group of users having parallax problems when lining up the function keys with the displayed option. Lines leading from each key to the surface of the display can alleviate this problem.

Other languages
Ideally users, including foreign visitors, should be able to choose the language; frequently this is only viable if the instructions are displayed on the screen or given audibly.

It would be preferable if the user's card stored their preferred language so that the terminal automatically switches to this as soon as the card is inserted.

Wireless links
Developments in infrared links make it feasible for a disabled user to have a hand control unit with an infrared link to the terminal. This would require all terminals to use the same interface protocol, and care would be needed to ensure confidentiality of sensitive information.

Alternatively a Bluetooth radio link to a telephone handset could be used.


Relevant standards
  • AS 3769 (1990) Automatic teller machines: User access.
  • EN 1332 Machine readable cards, related device interfaces and operations.
    • Part 1 Design principles and symbols for the user interface.
  • EN 29241 Ergonomic requirements for visual display terminals.
  • EN 894 Ergonomics of human-system interaction.
  • HFES 200.3. Human Factors Engineering of Software User Interfaces, Software interface standard (Standard now includes 5 interface strategies developed by Trace).
  • HFES 200.5. Human Factors Engineering of Software User Interfaces - Interactive Voice Response (IVR) and Telephony, A user interface standard for IVRs and voice mail.
  • ISO 9241 (1998) Ergonomic requirements for office work with visual display terminals.
  • ISO 13407 (1999) Human-centred design processes for interactive systems.
  • ISO DIS 9355-2 (1999) Ergonomic requirements for the design of displays and control actuators.
    • Part 1: Displays.
  • ISO/CD 13406 (1996) Ergonomic requirements for flat panel displays (Part 1-2).
  • ISO/CD 9355-1 (1999) Ergonomic requirements for the design of displays and control actuators.
    • Part 1: Human interaction with displays.
Further information


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