Guidelines

Touchscreens

A touchscreen is a computer display screen that is sensitive to human touch, allowing a user to interact with the computer by touching an active area, target or control such as pictures or words on the screen. As touchscreens become more common it is essential that they are designed for ease of use by everyone, including disabled and elderly people.

---

How do touchscreens work?

Touchscreens are activated by the insertion or removal of the fingertip or by pressing the controls, active areas or targets with a mouthstick, headstick, or other similar device (stylus). Some touchscreens support stylus input and others do not. The difference is in the device's touch sensor technology, of which there are several common types:

• Resistive touchscreens are pressure sensitive, so they can be operated with any input device, including a gloved hand or stylus. However, resistive screens can be easily damaged by sharp objects and they offer only 75% clarity, which may create additional problems for people with low vision.

• Capacitive touchscreens offer higher clarity and are more durable, but they do not respond to gloved hands or most styluses (the pointing device must be grounded).

• Infrared touchscreens can be operated by either human touch or stylus. They also provide high clarity and durability. However, they are more receptive to false responses (by dirt, flying insects, etc.) and do not respond well to users whose fingers hover before pressing a control.
• Surface acoustic wave (SAW), is a more advanced technology that provides high clarity and durability and can be operated by either human touch or stylus. This technology, however, is considerably more expensive than the more common technologies and is not as well supported.

Touch resolution

According to a Namahn report on touchscreens (2000), the resolution, or number of touch active points on the touchscreen, affects the level of pointing precision and selection errors. For example, the Namahn report states that, a capacitive screen has a touch resolution of 256 x 256 and an infrared screen has a resolution of 25 x 40 due to limitations on the number of light beams that can be placed around the screens. Therefore, a higher resolution screen provides additional touch points allowing greater pointing precision because the software can average all the points that have been touched and there are less selection errors as touch points are mapped more easily to the targets on the display.

Uses for touchscreens

The touchscreen is found on a wide variety of ICT applications:

Assistive Technology
The touchscreen interface can be beneficial to those that have difficulty using other input devices such as a mouse or keyboard. When used in conjunction with software such as on-screen keyboards, or other assistive technology, they can help make computing resources more available to people that have difficulty using computers.

Public Access Terminals
Information kiosks, tourism displays, trade show displays and other electronic displays are used by many people that have little or no computing experience. The user-friendly touchscreen interface can be less intimidating and easier to use than other input devices, especially for novice users. A touchscreen can help make information more easily accessible by allowing users to navigate by simply touching the display screen.

In today's fast pace world, waiting in line is one of the things that has yet to speed up. Self-service touchscreen terminals can be used to improve customer service at busy stores, fast service restaurants, transportation hubs, and more. Customers can quickly place their own orders or check themselves in or out, saving them time and decreasing wait times for other customers. Automated bank teller (ATM) and airline e-ticket terminals are examples of self-service stations that can benefit from touchscreen input.

Retail and Restaurant Systems
Time is money, especially in a fast paced retail or restaurant environment. Touchscreen systems are easy to use so employees can get work done faster and training time can be reduced for new employees. And because input is done right on the screen, valuable counter space can be saved. Touchscreens can be used in cash registers, order entry stations, seating and reservation systems.

Control and Automation Systems
The touchscreen interface is useful in systems ranging from industrial process control to home automation. By integrating the input device with the display, valuable workspace can be saved. And with a graphical interface, operators can monitor and control complex operations in real-time by simply touching the screen.

And many more uses...
The touch screen interface is being used in a wide variety of applications to improve human-computer interaction. Touchscreens are the most common means of input in personal digital assistants (PDAs). Other applications include digital jukeboxes, computerized gaming, student registration systems, multimedia software, financial and scientific applications and more.

 

Problems encountered by disabled and elderly people using touchscreens

Blind and Partially Sighted

As touchscreens do not provide tactile cues in order to activate a control, blind and partially sighted users rely on touchscreens that have the ability to provide audio clues for the location of the control. One such development in this field is the "Talking Fingertip Technique" (Vanderheiden, n.d.).

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

Hearing impaired

Hearing impaired users cannot identify commands or controls that require hearing, so visual or tactile feedback when controls are touched would be recommended.

Physically impaired

A person who has lost an arm or a hand may be using a prosthetic device. This may result in insufficient control to be able to accurately point at and press buttons or keys. Also, the prosthesis may be made of metal, plastic or some other material with dialectric properties that are different from those of a human finger, therefore a touchscreen will have to be able to detect this other material in order to react to the user's inputs.

Cognitively impaired

For those with cognitive impairments, labels that are made to look like controls can cause confusion. If screen designs and controls are constantly reconfigured so the design is flexible, this can render them difficult to use for cognitively impaired people, meaning that they are not given a chance to learn where the controls lie and what their associations are.

Elderly

Elderly people often experience changes in vision, hearing, dexterity and understanding as they age, therefore, they may encounter issues with identifying the location of controls on the touchscreen and being able to comfortably activate controls.

 

Other problems encountered in the use of touchscreens

Human touch
Whilst being used, the finger and hand obscure what is on the screen. Smudges left by fingers on the screen can decrease legibility.

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

The display should be viewable from the eye level of a person standing and from a person sitting in a wheelchair. People with low vision should not be prevented from getting their faces close to the screen.

Parallax problems
The conflicting requirements of tall users and short wheelchair users can lead to a significant group of users having parallax problems when lining up the controls with the displayed option. According to the Namahn report (2000), users tend to touch the sides of the screen and slightly below target areas, especially for targets near the top of the display and when the screen stands at a steep angle of between 45 and 90 degrees.

 

Checklist for Touchscreens

Recommendations

Screens

• The touchscreen should be shielded from sunlight
• The screen should be angled towards the horizontal to provide arm/wrist support
• The screen should be perpendicular to the line of sight
• The text and background colour combination should have high contrast
  
• Avoid shades of blue, green and violet for conveying information since they are problematic for older users
  
• There should be no noticeable flicker on the screen
  
• Structure the visual display layout so that the user can predict where to find required information and how to use it

Controls

According to Namahn (2000), touch sensitive areas or keys for users with no impairments, should be of a:

• "minimal size: 22mm across"

However, Colle & Hiszem (2004) recommend that:

• a "key size no smaller than 20mm...should be used if sufficient space is available"

Key size should be varied according to the size and use of the screen and the impairment type. For example, for one-handed thumb use of mobile handheld devices equipped with a touch-sensitive screen Parhi, Karlson and Bederson (2006) state that:

• "target size of 9.2mm for discrete tasks and targets of 9.6mm for serial tasks should be sufficiently large...without degrading performance and preference"

• Graphical symbols (such as icons) should be accompanied by text
• There should be high contrast between touch areas, text and background colour
• Text or controls should not be placed over a background image or over a patterned background
• White or yellow type on black or a dark colour is more legible, provided that the typeface, weight and size are suitable
• Controls are labelled in a large high contrast font
• Audible output or tactile output is provided for identification of controls and for results of activating controls
• An inactive space of at least 1mm should be provided around each target (Colle & Hiszem, 2004)
• Labels should be easily distinguishable from controls
• Controls should be operable by a mouthstick, headstick or other similar device (stylus)
• Commands can be entered by voice
• For wheelchair users the height of the active areas on the screen should be between 800mm and 1200mm
• The system must be error tolerant by providing a clear unambiguous control that permits the user to go back a step
• Position controls on the screen in a way that is consistent with functions
• All labels and instructions should be in short and simple phrases or sentences. Avoid the use of abbreviations where possible
• Provide text versions of audio prompts that are synchronised with the audio so that the timing is the same
• Speech output of instructions, as an addition to (and not a replacement for), on-screen instructions, is recommended
• Adhere to existing colour conventions e.g. red for stop

Help facilities

• Guidance should be readily distinguishable from other displayed information
• Provide the user with specific information relative to the task context rather than a generic message
• Provide information on how to recover from errors
• Indicate permitted range of values or syntax for user response
• Ideally, multi-modal help should be provided
• Allow skilled users the option of switching off help prompts if they are not required
• Keep spoken messages short and simple
• Do not use abbreviations in audio messages
• Allow users to interrupt the help at any time and return to the task
• An intelligent help facility is not an adequate solution to a poor user interface

 

Standards

• ISO 13406-1 (1999) Ergonomic requirements for work with visual displays based on flat panels. Part 1 - Introduction.
• ISO 13406-2 (2001) Ergonomic requirements for work with visual displays based on flat panels. Part 2 - Ergonomic requirements for flat panel displays.
• ISO 80416-4 (2005) Basic principles for graphical symbols for use on equipment. Part 4 - Guidelines for the adaptation of graphical symbols for use on screens and displays.
• ISO 9355-1 (1999) Ergonomic requirements for the design of displays and control actuators. Part 1: Human interactions with displays and control actuators.
• ISO 9355-2 (1999) Ergonomic requirements for the design of displays and control actuators. Part 2: Displays.
• ISO / IEC 24755 (2007) Information technology - Screen icons and symbols for peronal mobile communication devices.
• ITU-T E.902 (1995) Interactive services design guidelines.

Further information

• Gill, J. (2000) Access prohibited? Information for designers of public access terminals [accessed 31/02/08].
• Gill, J. Guidelines for the design of accessible information and communication technology systems: Controls. [accessed 04/02/08].
• Gill, J. Guidelines for the design of accessible information and communication technology systems: Public Access Terminals. [accessed 04/02/08].
• Gill, J. Guidelines for the design of accessible information and communication technology systems: Visual displays. [accessed 04/02/08].
• Jin, Z. X., Plocher, T. & Kiff, L. (2007) Touch screen user interfaces for older adults: button size and spacing. Universal access in human computer interaction. Coping with diversity, 4554/2007, 933-941, August 24.
• Schedlbauer, M. (2007) Effects of key size and spacing on the completion time and accuracy of input tasks on soft keypads using trackball and touch input. [accessed 05/02/08].
• Vanderheiden, G. (n.d.) Use of audio-haptic interface techniques to allow nonvisual access to touchscreen appliances. [accessed 04/02/08].
• Vanderheiden, G. (1997) Cross disability access to touchscreen kiosks and ATMs. Proceedings of the Seventh International Conference on Human-Computer Interaction: Volume 1, San Francisco, 24-29 August 1997, 417-420. New York: Elsevier Science Inc.
• Wikipedia (2008) Touchscreen. [accessed 04/02/08].
• Yfantidis, G. & Evreinov, G. (2006) Adaptive blind interaction technique for touchscreens. Universal Access in the Information Society, 4(4), 344-353, April.

Acknowledgements

• Colle, H. A. & Hiszem, K. J. (2004) Standing at a kiosk: effects of key size and spacing on touch screen numeric keypad performance and user preference. Ergonomics, 47(13), 1406-1423, October 22.
• Namahn (2000) Touch screens - the ergonomics: a Namahn brief. [accessed 06/02/08].
• The National Center on Accessible Information Technology in Education (n.d.) Are touch screens accessible? [accessed 04/02/08].
• NDA AccessIT (n.d.) Touchscreens. [accessed 04/02/08].
• Parhi, P., Karlson, A. K. & Bederson, B. B. (2006) Target size study for one-handed thumb use on small touchscreen devices. Proceedings of the 8th conference on human-computer interaction with mobile devices and services, Helsinki, 12-15 September 2006, 203-210. New York: ACM.
• Touchscreens.com (n.d.) What are touchscreens used for? [accessed 04/02/08].