Labels & icons
The position of labels with text or icons is crucial for an unfamiliar
user with impaired vision. All too often labels are positioned in a way
that they are obscured from the user's view when the controls are being
operated. The problem is particularly common when the control panel is
at an acute angle to the user's line of sight or at an inappropriate distance.
When deciding on the positioning of graphics or labels, the way people
who are left handed use the controls should also be considered. Also many
people with low vision like to get their face close to the control panel
to read the labels, or use face-mounted or hand-held magnifiers.
Active status
It is helpful if the user knows which controls are active at any one time. Sometimes this can be done by internally illuminating active keys; with complex displays in computer systems, inactive selections from a menu are often displayed with less brightness than the active selections. Blinking indicators should be restricted to situations requiring immediate action by the user; in these cases, they should be supplemented by an auditory signal.
Locating controls
For a totally blind person, it is first necessary to locate the control panel, and then select the relevant control. This is not a trivial task in many unfamiliar situations. Audible location signals can be used in some situations.
Ergonomics
The size and shape of a control knob can make a significant difference for a user with weak grip or for someone with cold hands. The choice of material can also affect the ease with which the knob can be gripped. The shape can help a visually impaired person select the correct knob; the shape can also be used to help the user associate the function with the key.
Braille
On outdoor terminals, Braille has limited value in cold weather since
tactual sensitivity is dramatically reduced with decreasing temperature.
The estimated number of Braille readers in Europe is less than 0.02% of
the population; so although useful for some blind users, Braille is not
a total solution for visually impaired users.
Colours
Colours commonly associated with functions can vary from country to country but in the UK red is normally associated with 'stop' or 'danger' and green with 'go' or 'ok'. With temperature controls, red is often associated with 'hot', amber with 'warm', and blue with 'cold'. Status should not be indicated by colour alone since a significant portion of the male population has problems distinguishing red/green or blue/yellow. Also it should be noted that people with retinitis pigmentosa often have difficulty reading red displays. In general, it is best to use strong (well saturated) colours.
Speech output
Optional speech output is becoming an increasingly viable alternative for speaking the names of keys as they are pressed. Hearing tends to deteriorate with age, and many elderly people have difficulty in hearing sounds above 3 kHz; often a low voice is easier to hear than a high one.
More time
Many older persons with impaired vision need more time to operate the system than is the standard allowed. For instance some of the newer public telephones time out such users before they have completed dialling the number. One possibility would be for the user to select 'compose and send' whereby they can dial the number at their own speed and then press the 'send' button to activate; the user's card could automatically select this option (see European standard EN 1332-4).
Consistency
It is important for there to be consistency in the direction of controls. The usual conventions are for an increasing value to be left to right, clockwise, or 'up' on a vertical slider. A logical layout of the user interface will make it easier for new users; a common format is for the user to work from left to right, but a vertical arrangement is often preferred by blind people. The logical grouping of keys can help on more complex keypads such as on interactive television remote controls.
Speech recognition
New technological developments will make it increasingly economically viable to incorporate speech recognition systems. If there is a limited vocabulary and low background noise, these systems work well for most people. The advantage for the user is that they do not have to take their eyes away from the task to operate a control. For most visually impaired persons speech input will be a boon if it is affordable and reliable.
Connecting other controls or equipment
For some users, it will be necessary to provide a special control system. This would be made much easier if there is some standard interface for connecting the special controls to the system. The connection can be done via a plug and socket, or by an infra-red or radio link. The advantage of the latter approach is that it electrically isolates the system from the external device, and does not require a disabled person to be able to reach and locate a plug in a socket.