Human Computer Interaction

Design rules for interactive systems

Design principles can guide the designer during the design process and can be used to evaluate and critique prototype design ideas. All the principles interact in complex ways, affecting each other, sometimes conflicting with each other and sometimes enhancing each other. But they help to orientate the designer to key features of good design and sensitize the designer to important issues.

Principles of Learnability

Learnability concerns the features of the interactive system that allow novice users to understand how to use it initially and then how to attain a maximal level of performance.


– determining effect of future actions based on past interaction history

– operation visibility


– assessing the effect of past actions

– immediate vs. eventual honesty


– how prior knowledge applies to new system

– guessability; affordance


– extending specific interaction knowledge to new situations


– likeness in input/output behaviour arising from similar situations or task objectives

Principles of Flexibility

The multiplicity of ways in which the user and system exchange information

Dialogue initiative

– freedom from system imposed constraints on input dialogue

– system vs. user pre-emptiveness


– ability of system to support user interaction for more than one task at a time

– concurrent vs. interleaving; multimodality

Task migratability

– passing responsibility for task execution between user and system


– allowing equivalent values of input and output to be substituted for each other

– representation multiplicity; equal opportunity

Principles of Robustness

Robustness covers features that support the successful achievement and assessment of goals.


– ability of user to evaluate the internal state of the system from its perceivable representation

– browsability; defaults; reachability; persistence; operation visibility


– ability of user to take corrective action once an error has been recognized

– reachability; forward/backward recovery; commensurate effortResponsiveness

– how the user perceives the rate of communication with the system

– Stability

Task conformance

– degree to which system services support all of the user’s tasks

– task completeness; task adequacy

Standards and Guideline for Interactive systems


• set by national or international bodies to ensure compliance by a large community of designers standards require sound underlying theory and slowly changing technology

• hardware standards more common than software high authority and low level of detail

• ISO 9241 defines usability as effectiveness, efficiency and satisfaction with which users accomplish tasks


• more suggestive and general

• many textbooks and reports full of guidelines

• abstract guidelines (principles) applicable during early life cycle activities

• detailed guidelines (style guides) applicable during later life cycle activities

• understanding justification for guidelines aids in resolving conflicts

Shneidermans’s 8 Golden Rules

These rules were obtained from the text Designing the User Interface by Ben Shneiderman. Shneiderman proposed this collection of principles that are derived heuristically from experience and applicable in most interactive systems after being properly refined, extended, and interpreted.

1. Strive for consistency

2. Enable frequent users to use shortcuts

3. Offer informative feedback

4. Design dialogs to yield closure

5. Offer error prevention and simple error handling

6. Permit easy reversal of actions

7. Support internal locus of control

8. Reduce short-term memory load

Norman’s 7 Principles

1. Use both knowledge in the world and knowledge in the head.

2. Simplify the structure of tasks.

3. Make things visible: bridge the gulfs of Execution and Evaluation.

4. Get the mappings right.

5. Exploit the power of constraints, both natural and artificial.

6. Design for error.

7. When all else fails, standardize.

Evaluation techniques for interactive systems

What is evaluation

Process which assesses the design and test the systems to ensure they perform as the requirement

Goals of evaluation

• assess extent of system functionality

• assess effect of interface on user

• identify specific problems

Evaluation through expert analysis

o Cognitive walkthrough

Usability evaluation method in which one or more evaluators work through a series of tasks and ask a set of questions from the perspective of the user.

— Proposed by Polson et al.

– evaluates design on how well it supports user in learning task

– usually performed by expert in cognitive psychology

– expert ‘walks though’ design to identify potential problems using psychological principles

– forms used to guide analysis

— For each task walkthrough considers

– what impact will interaction have on user?

– what cognitive processes are required?

– what learning problems may occur?

• Analysis focuses on goals and knowledge: does the design lead the user to generate the correct goals?

o Heuristic evaluation

Heuristic evaluation is that several evaluators independently critique a system to come up with potential usability problems.

• Proposed by Nielsen and Molich.

• usability criteria (heuristics) are identified

• design examined by experts to see if these are violated

• Example heuristics

– system behaviour is predictable

– system behaviour is consistent

– feedback is provided

• Heuristic evaluation `debugs’ design.

o Model-based evaluation

Model based evaluation is combining cognitive and design models to evaluation process.

• Cognitive models used to filter design options

e.g. GOMS prediction of user performance.

• Design rationale can also provide useful evaluation information

Evaluation through user participation

User participation in evaluation tends to occur in the later stages of development. This may range from a simulation of the system’s interactive capabilities, without its underlying functionality.

o Styles of evaluation

  1. Laboratory studies
  • Users are taken out of their normal work environment to take part in controlled tests.
  • Laboratory may contain sophisticated audio/visual recording and analysis facilities, two -way mirrors, instrumented computers.
  • There are , some situations where laboratory observation is the only option.

2. Field studies

The second type of evaluation takes the designer or evaluator out into the user’s work environment in order to observe the system in action.

Things that make field observation difficult

— High levels of ambient noise

— greater levels of movement

— constant interruptions

  • Field observation is to be preferred to laboratory studies
  • Even interruptions are important as these will expose behaviors.

• Controlled experiments can be useful for evaluation of specific interface features.

o Empirical methods: experimental evaluation

• controlled evaluation of specific aspects of interactive behaviour

• evaluator chooses hypothesis to be tested

• a number of experimental conditions are considered which differ only in the value of some controlled variable.

  • changes in behavioural measure are attributed to different conditions

Experimental factors

  • Subjects — who — representative, sufficient sample
  • Variables — things to modify and measure
  • Hypothesis — what you’d like to show

• Experimental design — how you are going to do it

o Observational techniques

  1. Think Aloud
  • user observed performing task
  • user asked to describe what he is doing and why, what he thinks is happening etc.
  • Advantages

— simplicity

— requires little expertise

— can provide useful insight

— can show how system is actually use

  • Disadvantages

— subjective

— selective

— act of describing may alter task performance

2. Cooperative evaluation

  • variation on think aloud
  • user collaborates in evaluation
  • both user and evaluator can ask each other questions throughout
  • Additional advantages

— less constrained and easier to use

— user is encouraged to criticize system

— clarification possible

3. Protocol analysis

  • paper and pencil — cheap, limited to writing speed
  • audio — good for think aloud, difficult to match with other protocols
  • video — accurate and realistic, needs special equipment, obtrusive
  • computer logging — automatic and unobtrusive, large amounts of data difficult to analyze
  • user notebooks — coarse and subjective, useful insights, good for longitudinal studies
  • Mixed use in practice.
  • audio/video transcription difficult and requires skill.
  • Some automatic support tools available

4. post-task walkthroughs

  • transcript played back to participant for comment

— immediately → fresh in mind

— delayed → evaluator has time to identify questions

  • useful to identify reasons for actions and alternatives considered

• necessary in cases where think aloud is not possible

o Query techniques

  1. Interviews

• analyst questions user on one-to -one basis usually based on prepared questions

• informal, subjective and relatively cheap

• Advantages

– can be varied to suit context

– issues can be explored more fully

– can elicit user views and identify unanticipated problems

• Disadvantages

– very subjective

– time consuming

2. Questionnaires

• Set of fixed questions given to users

• Advantages

– quick and reaches large user group

– can be analyzed more rigorously

• Disadvantages

– less flexible

– less probing

• Need careful design

– what information is required?

– how are answers to be analyzed?

• Styles of question

– general

– open-ended

– scalar

– multi-choice

– ranked

Evaluation through monitoring physiological responses

Evaluation through monitoring Physiological responses is a commonly used effective technique where developer can measure the experience of a user directly.

These are the two mainly observed areas in this techniques.

○ Eye Tracking

  • head or desk mounted equipment tracks the position of the eye
  • eye movement reflects the amount of cognitive processing a display requires

• measurements include

fixations: eye maintains stable position. Number and duration indicate level of difficulty with display

saccades: rapid eye movement from one point of interest to another

scan paths: moving straight to a target with a short fixation at the target is optimal

○ Physiological measurements.

• emotional response linked to physical changes

• these may help determine a user’s reaction to an interface

• measurements include:

– heart activity, including blood pressure, volume and pulse.

– activity of sweat glands: Galvanic Skin Response (GSR)

– electrical activity in muscle: electromyogram (EMG)

– electrical activity in brain: electroencephalogram (EEG)

• some difficulty in interpreting these physiological responses — more research needed

Universal Design for Interactive Systems

Universal design

The process of designing products that are accessible by all users in all circumstances, taking account of human diversity in disabilities, age and culture.

Universal Design Principles

In 1990s, North Carolina State University in the USA proposed seven universal design principles

1. Equitable use: the design is useful to people with a range of abilities and appealing (tempting) to all.

2. Flexibility in use: the design is adaptively to the user’s pace (speed), precision (accuracy), and custom(habit)

3. simple and intuitive to use: The system be simple and intuitive (perceptive) to use, regardless of the knowledge, experience, language or level of concentration of the user

4. Perceptible (observable) information: The design should provide effective communication of information regardless of the environmental conditions or the user’s abilities (e.g. graphic, verbal, text, touch).

5. Tolerance for error: minimizing the impact and damage caused by mistakes or unintended behavior

6. Low physical effort: systems should be designed to be comfortable to use, minimizing physical effort and fatigue (tiredness)

7. Size and space for approach and use: The placement of the system should be reached and used by any user regardless of body size, posture or mobility ( ie. seated or standing users)

Multi-modal interaction:

  • Provide access to system information and functionality through a range of different input and output channels
  • The 5 senses (sight, sound, touch, taste and smell) are used by us every day and provide a fuller interaction with the natural world
  • Computers rarely offer such a rich interaction

o Sound in the interface

Human beings have a great and natural mastery of speech

— makes it difficult to appreciate the complexities but — it’s an easy medium for communication

  • Different people speak differently: — accent, intonation, stress, idiom, volume, etc.

• The syntax of semantically similar sentences may vary.

  • Background noises can interfere.
  • Words not enough — semantics needed as well

— requires intelligence to understand a sentence

— context of the utterance often has to be known — also information about the subject and speaker e.g. even if “Errr…. I, um, don’t like this” is recognised, it is a fairly useless piece of information on it’s own

o Touch in the interface

haptic interaction

— cutaneous perception

  • tactile sensation; vibrations on the skin

— kinesthetics

  • movement and position; force feedback

Information on shape, texture, resistance, temperature, comparative spatial factors

example technologies

— electronic braille displays

— force feedback devices e.g. Phantom

• resistance, texture

o Handwriting recognition

Handwriting is another communication mechanism which we are used to in day-to-day life


— Handwriting consists of complex strokes and spaces

— Captured by digitising tablet

  • strokes transformed to sequence of dots

— large tablets available

  • suitable for digitising maps and technical drawings

— smaller devices, some incorporating thin screens to display the information

  • PDAs such as Palm Pilot
  • tablet PCs

Problems :

— personal differences in letter formation

— co-articulation effects

o Gesture recognition


— gestural input e.g. “put that there”

— sign language


— data glove

— position sensing devices e.g MIT Media Room

position sensing devices e.g MIT Media Room


— natural form of interaction — pointing

— enhance communication between signing and nonsigning users


— user dependent, variable and issues of coarticulation 

Designing Interfaces for diversity

The designer considers three key areas:

  1. Designing for users with disabilities

visual impairment

— The rise in the use of graphical interfaces reduces the possibilities for visually impaired users

hearing impairment

— have little impact on the use of an interface 

— Captioning audio content making audio files easier and more efficient to index and search

physical impairment

 — Users with physical disabilities vary in the amount of control and movement over their hands ,impact in mouse control difficulty 

— eyegaze system which tracks eye movements to control the cursor, 

— keyboard driver that can be attached to the user’s head. 

— predictive system, such as the Reactive keyboard, cut the typing requirement considerably

speech impairment

— multimedia systems provide a number of tools for communication, including synthetic speech and text-based communication and conferencing systems


— Users with cognitive disabilities such as dyslexia can find textual information difficult


— affects a person’s ability to communicate and interact with people around them and to make sense of their environment

  1. Social interaction — problems
  2. Communication — problems
  3. Imagination — problems

— How might universal design of technology assist people with autism? communication and education.

2) Designing for different age groups

Older people:

— email and instant messaging, can provide social interaction in cases where lack of mobility or speech difficulties and reduce face-to-face possibilities.


— Information in Graphics, sound and text, Pen-based interfaces, touch or handwriting, may be easier for children than keyboard and mouse

3) Designing for cultural differences

— The other factors such as age, gender, race, sexuality, class, religion and political persuasion, may all influence an individual’s response to a system.  — The designer practice universal design which include language, cultural symbols, gestures and use of color.



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