Direct controls activate a function without any other operation or feedback required. Indirect controls are ones by which the operation requires some other action such as reading a visual display. For example, setting a video recorder using an on-screen display. Another example would be a rotary control which adjusts the oven timer on the basis that the timechanges according to the speed of rotation of the control.
Certain controls are more applicable to some tasks than other controls, the best design depends on the demands of the task. The usability of a control can be influenced by its shape, ease of discrimination, control - response ratio, resistance and location. When controls are well designed, reaction times are reduced and greater precision is executed. The control procedures are also learnt faster. Thinking about the characteristics of the user, system, and the interactions between them will enable a designer to try to improve a system's usability by finding any areas that make a task difficult.
Locating Control Area
At A Glance
Salient features will be most noticeable in situations where only a short time is available to deduce control information. So creating distinct controls would enable sighted and partially sighted people to find controls quickly. Discriminability is paramount because people spend longer discriminating between features that are similar than those that are radically different. Obviously as the size of a control increases, the easier it is to see it, and the easier it is to locate it because it would occupy more space. Size is often assumed to be an indication of importance with larger items being displayed superior to smaller ones. A bright saturated colour amidst a dull array of controls will be very noticeable. But the same control placed amongst other colourful controls will not stand out in the same way. Arrays which are symmetrical are more aesthetically pleasing but can become monotonous. Asymmetrical arrays which are characterised as having more visual weight on one side of the central axis than on the other, are interpreted as being more informal.
Finger / Hand Reference Points
If a lot of controls are presented together but not easily recognisable or grouped in a comprehensible way, then the user's fingers can get lost amongst the array. Distinct features identifiable by shape, size etc. can be used as reference anchor points for the fingers or palm to facilitate finding specific controls.
Distinguishing features of various controls can be used to create a starting place from which other functions can be easily found or these can be designed to be used in this manner, similar to tactile maps. Tactile maps use symbols to indicate specific locators.
Location and Clustering
Blind positioning movement involves reaching for a control when the person's eyes are busy. Research into this area reveals that these are most accurate when the controls are placed straight in front of the person. The accuracy of reaching for controls decreases the further to either side they are placed. People tend to be more sensitive to differences in location vertically as opposed to horizontally. So the spacing between controls should be greater in a horizontal direction. Controls located between waist and shoulder height are more accurately found than those above head height. Optimally controls should be placed straight ahead and at or below shoulder level.
Devices are easier to use when the controls are placed in a logical manner. Some principles for control arrangement are:
- Frequency of use - controls which are used frequently should be placed in a convenient location if appropriate between elbow and shoulder height. This is useful for complicated systems where they are numerous functions.
- Importance principle - important controls should be located in a convenient place.
- Sequence of use - the layout should reflect the sequence of operation. This is useful for simple systems. For example horizontally, the first button to use is placed at the far left, the second is placed to the right of that and so on. Visually impaired people find it easier to read from left to right rather than in columns or right to left.
- Functional grouping principle - places closely related functions next to one another whilst making them easily and clearly identifiable. These could share spatial, physical or temporal attributes. Groups can be distinguished by spacing, colour, shape, size, boundary borders.
- Colocation - this relates to the compatibility of displays and their controls. The layout of the controls should reflect their displays so their relationship is evident.
- Consistency principle - the layout with the shape components located in the same spatial location would minimise memory and search requirements. Using consistent labels and messages will reduce the risk of creating errors.
Some principles are more powerful e.g. sequence of use and functional grouping principles. Any of these principles may conflict so discernment is required when applying these principles to a specific design.
Controls which are rarely used but required on the console could be positioned under a hidden panel so they are still accessible but do not clutter the important functions.
With greater space between controls, inadvertent operation errors decrease but performance is also affected. If controls are placed too far apart, they will require a lot of movement which could become tiring over time. If controls are placed too close together, inadvertent operation of more than one control is possible. Errors of touching other controls are greatest for knobs to the right of the one to be operated and least for the controls to the left.
- Clutter avoidance principle - refers to adequate space between adjacent controls.
Crowding controls together decreases the amount of 'white space' around them, creates spatial tension and inhibits scanning. It can also produce distracting effects when lines are too close.
When control area space is at a premium, smaller diameter controls result in less errors whilst maintaining performance. For different control configurations, the optimum size of clustering would need to be tested.
Designing for more than one sense modality is preferred because people vary widely in their capabilities and it helps compensate for overloading of one or more senses. Control identification is created through coding the controls size, shape, texture, colour, location, labels and operation method. Which of these factors are relevant and their parameters depends of the detectability, discriminability, compatibility, meaningfulness and standardisation of the codes. Incorporating more than one sense into a design can compensate for a sensory channel that has been adversely affected e.g. in a cold environment, peoples' tactile sensitivity is lessened and wearing gloves will also decrease this. People with diabetes may have decreased tactile sensitivity.
Tactile sensitivity is essential to discriminate shapes of controls especially when vision can not be used. This is helpful to everyone especially in darkened environments. Basic forms like round shapes are memorable, simple and pleasing to the eye. Military research has designed controls so they are not often confused with one another. If these shapes are related to the control's function, they are even easier to correlate and remember. This symbolic association is used in cockpit design, it could also enable blind people to identify controls.
For tactile shapes, outlined circles are the easiest to distinguish - this is thought to be because there are two edges to feel. But at smaller sizes, the double edge of the outlined circle may be a source of confusion if two lines are expected but only the outer one is clearly felt.
The control's material can affect the ease of use with which a control is operated. Textures can be rough, smooth, thick, thin, soft, hard, regular or irregular. Textures can be broken down into their:
- Intensity - dot density
- Spacial cues - spacing
- Angular orientation
Research with controls of differing textures has indicated that smooth controls are not confused with any others. Textures are distinctive when their elements are tightly spaced along one axis but widely spaced along other axes. Diagonal and diamond patterns are confused with each other especially at high intensities. Vertical patterns are recognisable at high densities whereas other orientations are evident at lower intensities. 'Fluted' designs were confused with one another but not with other types of texture. Similarly, 'knurled' designs were confused with other knurled designs but not with other designs. High and low density patterns are easier to distinguish from one another than those with medium density. Textures should be chosen for their contrasting characteristics because similar surfaces can be easily confused. Controls need to be maintained so that markings and grooves are not obscured by dirt.
Mobiles have been created with tiny arrays of moving pins that enable people to distinguish tactile melodies. This could translate into tactile actuator arrays built into steering wheels to provide car drivers or pilots with information as to the right route or warn them in difficult situations.
Colour can be informative when used to link information as long as it is used in moderation. It does this by linking elements together, to indicate organisation and relationships. Colour helps in searching tasks by drawing attention.
Optimally 2-4 colours should be used. But colour can be distracting if overused so only colour a few items. Also users must look at a colour to be able to identify it. Red can be associated with 'stop' or 'danger' but a significant proportion of the male population in the UK is red/green colour blind. Some people with retinitis pigmentosa may have difficulties reading a red display. A lesser proportion of the population is blue/yellow colour blind. Colours used should not cause adverse visual after effects. Colour coding should not cause problems during the night. Poor illumination, dirt or lack of vision can obscure this form of coding but combining colour with another coding method can increase discriminability.
Information should only be presented that is directly pertinent to the task and must be placed appropriately. Long explanations using jargon can be time consuming to read and difficult to comprehend especially by people with poor language skills. They should be unambiguously precise, concise and clearly visible using a contrasting and appropriate typeface. Fixed size small text can be difficult for older users or people with low vision to read. Labels should be placed above the control so the hand does not cover them when reaching for it. Using only labels to identify controls is not desirable and impossible without vision. Embossed makings on some controls can help identification. People with low vision may appreciate being able to place their faces' or magnifiers close to the labels.
Understanding the meaning of icons
Icons used on buttons and controls must be easy to understand. Currently the 'enter' button on most keypads uses a 'return' arrow which is a left-over from the old style typewriters where this icon indicated a 'carriage return'; the meaning is not obvious unless you are old enough to remember moving carriage typewriters. In many cases it would be better to use the appropriate words rather than leave the users to guess the meaning of the icons.
It is important to keep icons as distinct and simple as possible, they should provide enough information to convey the message because too much information causes people to take longer to recognise them.
Controls should say what they do and do what they say. This is reinforced if they are intuitive to use and easy to remember. There needs to be consistency both within and across applications. Additionally controls should be compatible with how people expect them to move e.g. up is up and left is left. Any display associated with the controls should be aligned appropriately. Using concepts that are familiar to the users will enable people to accurately guess at how a function will operate. This should correspond to their expectations e.g. the direction of reading is a powerful transferable stereotype.
The size of controls and their spacing should be determined with reference to the people's fingers.
The muscles from which the thumb derives power are located within the palm of the hand (unlike the muscles for the fingers). This means that especially when the hand is not located in a neutral position that the thumb is more powerful and will tire less easily than the other fingers. The design implications are that tasks that require repetitive control presses should be designated to the thumb.
Relative or absolute controls
Controls which change the relative, rather than absolute values often cause problems for people with low vision. A blind person may find it difficult to judge where a slider switch is positioned in relation to the upper and lower limits of the scale. A person with decreased manual dexterity may find it difficult to operate a control which has to be moved from side to side.
To operate a control, force is required to move it which results in a change in position. If this is too great, people with reduced strength may find the controls difficult to activate. So the resistance of a control should be comfortably within the capabilities of weaker members of the user population.
Force and displacement provide feedback to the user. In many situations - even though controls which manipulate only one variable are possible - a combination of both are useful.
Clear and precise feedback and explanations will enable the use of the system without any training. Each state should be identifiable. Experiments with a multi-modal mouse indicated that tactile feedback produced a faster response time. Tactile feedback could be shown by the difference in position of a control which is obvious with some types of controls such as a lever switch, rocker switch. The fewer positions that each switch uses, the easier the position is to identify.
Non-tactile feedback is possible if proximity switches are combined with audio output. Audio or speech output is becoming increasingly viable to confirm the correct options that have been entered. When a finger is held close to a control, its function would be spoken. If the person requires the control they could then activate it in the usual manner. A click or beep when the control is activated would provide activation feedback too.
The larger the delay in feedback - until the delay exceeds about 2 seconds - the more adversely performance is affected. After a delay of 2 seconds, people tend to wait for a control to catch up with them before they perform another action.
The design should aim for the users to avoid errors and be error tolerant if they occur. Undo or cancel buttons should be available so tasks are reversible. Error messages should reveal what the fault is and how to remedy it. These messages should be simple and consistent.
A warning must be sensed, understood and prompt appropriate action.
In quiet surroundings to detect an audible signal it would need to be about 40 - 50 dB above the absolute threshold. The ear does not respond to instantaneous sound so for pure tones, it takes about 200 - 300ms to build up and about 140ms to decay; wideband sounds build up and decay more quickly. So auditory sounds should be at least 500ms (0.5s) in duration, if they are shorter they do not sound as loud, so their intensity should be increased.
In noisy conditions, the signal must be above the background noise without being annoying or damaging. The loudness should be 10-15 dB over the ambient noise but with a maximum of 90 dB. Signals presented to both ears rather than one are more effective.
Caution must be taken to not cause 'warning overload'. When there is a warning for every hazard, the warnings become diluted and do not elicit a response and are ineffective.
Some guidelines for audio warning signals include:
- Use frequencies between 300 - 3000Hz because the ear is most sensitive to this range.
- Attending to audible information may reduce the processing of other audio sounds. Use signals with frequencies that differ from any background noise to minimise masking the warning sound.
- Use a modulated signal (1 - 8 beeps / s) (1 - 3 times / s for warbling sounds) because it differs from normal sounds to demand attention.
- If different warning signals are used to differentiate between responses required, they should be clearly discriminable.
Types of Controls
Buttons at the side of the screen can be difficult to align with the text on the display if the user is not looking perpendicular to the screen. Displays should not look like controls. Buttons which act as toggles (i.e. one push for 'on', another push for 'off') should be provided with tactual and auditory feedback.
Push buttons also provide tactile feedback by a decrease in force required to push the control. When the top of the control is concave, a fingertip naturally falls towards the centre of the control and is less likely to slip off.
Many elderly people are confused if they are presented with too many buttons; keys which are infrequently used can be positioned behind a cover.
Keypads have advantages over other forms of device for data entry.
Numeric keypads following the telephone layout are slightly faster and more accurate to use than the calculator layout. With numeric keys there is a convention to put a raised dot on the number '5'. It is important to ensure this does not decrease legibility by obscuring the visual markings. Unfortunately this does not help distinguish between the calculator or telephone layout.
Membrane keypads such as those used on microwave ovens lack the familiar key-stoke feedback because there is no noticeable displacement regardless of the force exerted. They often require more force to activate than push-buttons to avoid inadvertent operation. Errors tend to be omissions due to key-stokes not being registered. Auditory tones have been found to provide activation feedback whilst reducing errors. The actual contact areas are difficult to locate especially for visually impaired people. A raised rim and tactile markings would clarify this. Without the tone, embossing alone fails to improve performance, so both activation and finger position feedback are important design considerations.
When space for the control panel is very limited, such as on wearable systems, it may be necessary to provide a socket by which the device can be connected to an alternative keypad. Another option would be an infra-red or radio link such as Bluetooth. Chording keypads, where more than one key has to be pressed at the same time, permit a compact control panel but they can be difficult to learn to use.
These are thought to be useful in situations where inputs are limited and well defined. On one screen controls can be reconfigured so the design if flexible. This can render them difficult to use for visually impaired people who are not given a chance to learn where the controls lie and their association. It is important to ensure that labels are not made to look like controls. Problems with parallax can also limit the effectiveness of touchscreens.
Whilst being used, the finger and hand obscure what is on the screen. Smudges left by fingers on the screen can decrease legibility. Touchscreens can be very difficult for blind people to use because it is difficult to locate the control / active area and know whether this has been activated. However it is possible to design the system so that there is spoken output when the finger is over an item on the screen, but activation is only when the finger is withdrawn over an active area. With this arrangement there should be only a small number of well spaced active areas.
It can be tiring to hold your arm up for a long time and pointing is not very accurate, people tend to hit below the target. Accuracy is best for targets nearer the bottom of the screen this is thought to be due to the position of the arm and parallax problems. The vertical size of the target affected the error rates. To decrease the errors made by activating the wrong button, large touch sensitive areas or soft buttons with a minimum of 20 mm height and width are recommended.
These are common in vehicles especially aircrafts. Thorough testing is important for any multifunction controls in the context of a system. Several principles are relevant to the design of multifunction hand controls:
- The controls should be operable without vision
- The hand should remain in contact with the primary controls throughout critical operations of the system
- Secondary controls should be activated without loss of contact to the primary controls
- DTR/HF 02009 (1996) Characteristics of telephone keypads.
- EN 29241 Ergonomic requirements for visual display terminals.
- ES 201 381 (December 1998) Telecommunication keypads and keyboards: Tactile identifiers.
- ETR 345 (Jan 1997) Characteristics of telephone keypads and keyboards; Requirements of elderly and disabled people.
- IEC 73 (1990) Colours of pushbuttons and their meanings.
- ISO 447 Machine tools: Direction of operation of controls.
- ISO 1503 Geometric orientation and directions of movement.
- ISO 13407 Human-centered design processes for interactive systems.
- ISO 9241 International standards for colour use.
- ISO DIS 9355-2 (1999) Ergonomic requirements for the design of displays
and control actuators.
- Part 1: Displays.
- ISO/CD 9355-1 (1999) Ergonomic requirements for the design of displays
and control actuators.
- Part 1: Human interaction with displays.
- ISO/IEC 9995 (1994) Information technology: Keyboard layouts for text and office systems.
- ITU-T E.902 (1995) Interactive services design guidelines.
- ITU-T Rec. H.245, Control Protocol for Multimedia Communication, Multimedia Control protocol.
- ITU-T Recommendation H.224, A real time control protocol for simplex applications using the H.221 LSD/HSD/HLP channel., Addition of client id=2 for T.140 text transport.
- ITU-T Recommendation H.248, Gateway control protocol, Text conversation
protocol for multimedia application. With amendment 1 (2000). Control
of gateway between all forms of text conversation.
- Part 4 Keyboard requirements.
- TCR-TR 023 (1994) Assignment of alphabetic letters to digits on
push button dialling keypads.
- An Anthropometric Table produced by DTI.
- Designing User Interfaces for People with Visual Impairments
- Consumer products - Guidelines to increase accessibility to people with disabilities or who are ageing.
- Beaton, R. and Weiman, N. (1984). Effects of Touch Key Size and Separation on Menu - Selection Accuracy. (Tech. Rep. No. TR 5000-01. Tektronix, Human Factors Reseach Laboratory: Beaverton.
- Blankenship, E. (2003). An Introduction to Designing User Interface Controls at SAP.
- Bradley, J.V. (1967). Tactual Coding of Cylindrical Knobs. Human Factors, Volume 9, No. 5. pp 483 - 496.
- Bradley, J.V. (1969). Optimum Knob Crowding. Human Factors, Volume 11, No 3. pp 227 - 238
- Hunt, D.P. (1953). The Coding of Aircraft Controls (Tech. Rept. pp51 - 221). U.S. Air Force, Wright Air Development Centre.
- Sakamura K Tron Human-Machine Interface Specifications. Tron Association, 1993.
- Sanders, M.S. and McCormick, E.J. (1992). Human Factors in Engineering and Design. McGraw-Hill Inc. Singapore. ISBN: 0-07-112826-3
- Wierwille, W. (1984). The Design and Location of Controls: A Brief Review and an Introduction to New Problems. In H. Schmidtke [Ed.]. Ergonomic Data for Equipment Design. Plenum: New York.