Human Computer Interaction

Hansa Sandamal
18 min readDec 26, 2020


Design rules for interactive systems

Design rules are rules that a designer can follow in order to increase the usability of the system or product.

We can these rules into three categories. Those are principles, standards and guidelines.

Principles -Abstract and have high generality & low in authority. Widely applicable and enduring. e.g. interface should be easy to navigate

Guidelines - Can guide or advise on how achieve a principle Narrowly focused. Can be too specific, incomplete, & hard to apply but they are more general and lower in authority than Standards. e.g. use this button to save data

Standards- which are very specific & high in authority. e.g. use colour RGB #1010D0 on home links

Usability Principles

Principles of Learnability —

the ease with which new users can begin effective interaction and achieve maximal performance (e.g. Predictability, Synthesizability, Familiarity, Generalizability, Consistency.)

Predictability: support for the user to determine the effect of future action based on past interaction history.

Synthesizability: support for the user to assess the effect of past operations on the current state.

Familiarity: the extent to which a user’s knowledge and experience in other real world or computer-based domains can be applied when interacting with a new system.

Generalizability: support for the user to extend knowledge of specific interaction within and across applications to other similar situations.

Consistency: likeness in input-output behavior arising from similar situations or similar task objectives.

Principles of Flexibility—

the multiplicity of ways the user and system exchange information (e.g. Dialogue initiative, Multithreading, Task migratability, Substitutivity, Customizability.)

Dialogue initiative: user freedom from artificial constraints on the input dialog imposed by the system.

Multithreading: the ability of the system to support user interaction for more than one task at a time.

Task migratability: the ability to transfer control for execution of tasks between the system and the user (e.g. spell-checking task).

Substitutivity: the extent to which an application allows equivalent input and output values to be substituted for each other

Customizability: the ability of the user or the system to modify the user interface.

Principles of Robustness—

the level of support provided to the user in determining successful achievement and assessment of goal-directed behavior (e.g. Observability, Recoverability, Responsiveness, Task conformance)

Observability: the extent to which the user can evaluate the internal state of the system from the representation on the user interface.

Recoverability: the extent to which the user can reach the intended goal after recognizing an error in the previous interaction.

Responsiveness: a measure of the rate of communication between the user and the system.

Task conformance: the extent to which the system services support all the tasks the user would wish to perform and in the way the user would wish to perform.

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.

Ben Shneiderman’s 8 Golden Rules

To improve the usability of an application it is important to have a well designed interface. Shneiderman’s “Eight Golden Rules of Interface Design” are a guide to good interaction design.

  1. Strive for consistency: layout, terminology, command usage, etc.

2. Cater for universal usability: recognize the requirements of diverse users and technology. For instance add features for novices eg explanations, support expert users eg shortcuts.

3. Offer informative feedback: for every user action, offer relevant feedback and information, keep the user appropriately informed, human-computer interaction.

4. Design dialogs to yield closure: help the user know when they have completed a task.

5. Offer error prevention and simple error handling: prevention and (clear and informative guidance to) recovery; error management.

6. Permit easy reversal of actions: to relieve anxiety and encourage exploration, because the user knows s/he can always go back to previous states.

7. Support internal locus of control: make the user feel that s/he is in control of the system, which responds to his/her instructions/commands.

8. Reduce short-term memory load: make menus and UI elements/items visible, easily available/retrievable.

Evaluation techniques for interactive systems

What is evaluation 

Evaluation role is to access designs and test systems to ensure that they actually behave as we expect and meet user requirements. Ideally, evaluation should occur throughout the design life cycle, with the results of the evaluation feeding back into modifications to the design.

Goals of evaluation 

Evaluation has three main goals:

To assess the extent and accessibility of the system’s functionality -

Evaluation at this level may measuring the user’s performance with the system to assess the effectiveness of the system in supporting the task.

Eg: if a filing clerk is used to retrieving a customer’s file by the postal address, the same capability (at least) should be provided in the computerized file system.

To assess users’ experience of the interaction -

Important to assess the user’s experience of the interaction and its impact upon user. How easy the system is to learn, its usability and the user satisfaction with it. It may include his enjoyment and emotional response, particularly in the case of aim to entertainment.

To identify any specific problems with the system.-

This may aspects of the design which, when used in their intended context, cause unexpected results, or confusion amongst user. Related to both the functionality and usability of the design

Evaluation through expert analysis

Cognitive walkthrough

Originally proposed by Polson and colleagues as an attempt to introduce psychological theory into the informal and subjective walkthrough technique. The main focus is to establish how easy a system is to learn (by hands on, not by training or user’s manual).

To do a walkthrough,

1. A specification or prototype of the system (doesn’t have to be complete, but it should be fairly detailed. Details such as the location and wording for a menu can make a big difference.)

2.A description of the task the user is to perform on the system. This should be a representative task that most users will want to do

3.A complete, written list of the actions needed to complete the task with the proposed system

4.An indication of who the users are and what kind of experience and knowledge the evaluators can assume about them

For each task walkthrough considers

●what impact will interaction have on user?

● what cognitive processes are required?

●what learning problems may occur?

Heuristic evaluation

Proposed by Nielsen and Molich. Heuristic is a guideline or general principle or rule of thumb that can guide a design decision or be used to critique a decision that has already been made. Design examined by experts to see if these are violated (3 to 5 enough).Eg: system behavior is predictable, system behavior is consistent, feedback is provided

Nielsen’s ten heuristics are:

  1. Visibility of system status-

Always keep users informed about what is going on, through appropriate feedback within reasonable time. Eg: if a system operation will take some time, give an indication of how long and how much is complete.

2. Match between system and the real world

system should speak the user’s language, with words, phrases and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in natural and logical order.

3. User control and freedom

Users often choose system functions by mistake and need a clearly marked ‘emergency exit’ to leave the unwanted state without having to go through an extended dialog. b. Support undo and redo

4. Consistency and standards

Users should not have to wonder whether words, situations or actions mean the same thing in different contexts. Follow platform conventions and accepted standards.

5. Error prevention

Make it difficult to make errors. Even better than good error messages is a careful design that prevents a problem from occurring in the first place.

6. Recognition rather than recall

Make objects, actions and options visible. The user should not have to remember information from one part of the dialog to another. Instructions for use of the system should be visible or easily retrievable whenever appropriate.

7. Flexibility an efficiency of use

Allow users to tailor frequent actions. Accelerators unseen by the novice user may often speed up the interaction for the expert user to such an extent that the system can cater to both inexperienced and experienced users.

8. Aesthetic and minimalist design

Dialogs should not contain information that is irrelevant or rarely needed. Every extra unit of information in a dialog competes with the relevant units of information and diminishes their relative visibility.

9. Help users recognize, diagnose and recover from errors

Error messages should be expressed in plain language (no codes), precisely indicate the problem, and constructively suggest a solution.

10. Help and documentation

Any such information should be easy to search, focused on the user’s task, list concrete steps to be carried out, and not be too large.

Model-based evaluation

Dialog models can be used to evaluate dialog sequences for problems, eg. Unreachable states, circular dialogs and complexity. Models such as state transition networks are useful for evaluating dialog designs prior to implementation.

Evaluation through user participation

User participation in evaluation tends to occur in the later stages of development when there is at least a working prototype of the system in place.

Styles of evaluation

Laboratory studies-

It take part in controlled tests. Users are taken out of their normal work environment to take part in controlled tests, often in a specialist usability laboratory


specialist equipment available :Contain sophisticated audio/visual recording and analysis facilities, two-way mirrors, instrumented computers and the like, which cannot be replicated in the work environment

uninterrupted environment: the participant operates in an interruption-free environment .


lack of context : The unnatural situation may mean that one accurately records a situation that never arises in the real world

difficult to observe several users cooperating .

This is appropriate if system location is dangerous or impractical for constrained single user systems to allow controlled manipulation of use

Field studies -

into the user’s work environment in order to observe the system in action.


natural environment: Observe interactions between systems and between individuals that would have been missed in a laboratory study

context retained (though observation may alter it): seeing the user in his ‘natural environment’.

longitudinal studies possible.


Distractions : High levels of ambient noise, greater levels of movement and constant interruptions, such as phone calls, all make field observation difficult


This is appropriate where context is crucial for longitudinal studies.

Empirical methods: experimental evaluation

Controlled evaluation of specific aspects of interactive behavior. Evaluator chooses hypothesis to be tested and provides empirical evidence to support a particular claim or hypothesis. A number of experimental conditions are considered which differ only in the value of some controlled variable. Changes in behavioral measure are attributed to different conditions.


Should be chosen to match the expected user population as closely as possible. And sample size must be large enough to be representative of the population.


Stating that a variation in the independent variable will cause a difference in the dependent variable. By disproving the null hypothesis, which states that there is no difference in the dependent variable between the levels of the independent variable.

null hypothesis: States no difference between conditions, aim is to disprove this . e.g. null hyp. = “no change with font size”


Things to modify and measure. Clarify the independent and dependent variables, in that you will have identified what you are going to manipulate and what change you expect .

○ Independent variables IV — characteristic changed to produce different conditions. (e.g. interface style, number of menu items)

○ Dependent variables DV — characteristics measured in the experiment. (e.g. time taken, number of errors.)

Experimental design ;

How many participants are available and are they representative of the user group?. There are two main methods:

between-subjects(or randomized): participant is assigned to a different condition (experimental and control conditions)

within-subjects(or repeated measures): each user performs under each different condition.

Observational techniques

  1. Think Aloud :

Observation where the user is asked to talk through what he is doing as he is being observed. Ex. Describing what he believes is happening, why he takes an action, what he is trying to do. The evaluator can clarify point of confusion.

Advantages :

simplicity: requires little expertise

can provide useful insight with an interface

can show how system is actually use

Disadvantages :


Selective: depending on the tasks provided

Act of describing may alter task performance : The process of observation can alter the way that people perform tasks and so provide a biased view

2. Cooperative evaluation :

variation on think aloud .user collaborates in evaluation :encouraged to see himself as a collaborator in the evaluation and not simply as an experimental participant. 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 :

Methods for recording user actions include the following.

•Paper and pencil

•Audio recording

•Video recording

•Computer logging (Ex. Record user actions at a keystroke)

•User notebook (Ex. Participants be asked to keep logs of activity/problems.)

•audio/video transcription difficult and requires skill.

•Some automatic support tools available.

4.Automated analysis-EVA :

Analyzing protocols, video, audio or system logs ,is time consuming and tedious by hand, provide automatic analysis tools to support the task

EVA ( Experimental Video Annotator) -a system that runs on a multimedia workstation with a direct link to a video recorder

Advantages :

analyst has time to focus on relevant incidents

avoid excessive interruption of task

Disadvantages :

lack of freshness

may be post-hoc interpretation of events

5.Post-task walkthroughs:

To reflect the participant’s actions back to them after the event, by asking comment, or directly question. This is only way to obtain a subjective viewpoint on the user’s behavior. Useful to identify reasons for actions and alternatives considered .Necessary in cases where think aloud is not possible. Eg. the participant may say ‘and now I’m selecting the undo menu’, but not tell us what was wrong to make undo necessary.

Query techniques


The level of questioning can be varied to suit the context and that the evaluator can probe the user more deeply on interesting issues as they arise.

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


Less flexible than interview technique, questions are fixed in advance. But it can reach wider participant group and take less time.

Styles of question;

General (Ex. Age, sex, occupation, experience, etc.).

Open-ended (Ex. Can you suggest any improvements to the interface?).




Advantages :

quick and reaches large user group

can be analyzed more rigorously


less flexible

less probing

Evaluation through monitoring physiological responses

Eye tracking

Head or desk mounted equipment tracks the position of the eye and movement reflects the amount of cognitive processing a display requires.

measurements include;

Number of fixations (The more fixations the less efficient the search strategy)

Fixation duration(Indicate level of difficulty with display)

Scan path(moving straight to a target with a short fixation at the target is optimal)

saccades(rapid eye movement from one point of interest to another)

Physiological measurement

Emotional response linked to physical changes. These may help determine a user’s reaction to an interface.

measurements include:

Heart activity; blood pressure, volume and pulse.

Activity of the sweat glands; galvanic skin response(GSR)

Electrical activity in muscle; electromyogram (EMG)

Electrical activity in the brain; electroencephalogram(EEG)

Universal Design for Interactive Systems

Universal design is the process of designing products so that they can be used by as many people as possible in as many situations as possible. Universal design is about designing systems so that they can be used by anyone in any circumstance.

Universal Design Principles

In the late 1990s a group at North Carolina State University in the USA proposed seven general principles of universal design. These were intended to cover all areas of design and are equally applicable to the design of interactive systems. These principles give us a framework in which to develop universal designs.

1.Equitable use.

The design is useful and marketable to people with diverse abilities. No user is excluded or stigmatized. Wherever possible, access should be the same for all; where identical use is not possible, equivalent use should be supported. Where appropriate, security, privacy and safety provision should be available to all. For example, a website that is designed to be accessible to everyone, including people who are blind and use screen reader technology, employs this principle.

2. Flexibility in Use.

The design accommodates a wide range of individual preferences and abilities, through choice of methods of use and adaptivity to the user’s pace, precision and custom. An example is a museum that allows visitors to choose to read or listen to the description of the contents of a display case.

3. Simple and intuitive.

Use of the design is easy to understand, regardless of the knowledge, experience, language or level of concentration of the user. The design needs to support the user’s expectations and accommodate different language and literacy skills. It should not be unnecessarily complex and should be organized to facilitate access to the most important areas. It should provide prompting and feedback as far as possible. Science lab equipment with clear and intuitive control buttons is an example of an application of this principle.

4. Perceptible information.

the design should provide effective communication of information regardless of the environmental conditions or the user’s abilities. Redundancy of presentation is important: information should be represented in different forms or modes (e.g. graphic, verbal, text, touch). Essential information should be emphasized and differentiated clearly from the peripheral content. Presentation should support the range of devices and techniques used to access information by people with different sensory abilities. An example of this principle is captioned television programming projected in a noisy sports bar.

5. Tolerance for error.

Minimizing the impact and damage caused by mistakes or unintended behavior. Potentially dangerous situations should be removed or made hard to reach. Potential hazards should be shielded by warnings. Systems should fail safe from the user’s perspective and users should be supported in tasks that require concentration. An example of a product applying this principle is software applications that provide guidance when the user makes an inappropriate selection.

6. Low physical effort.

Systems should be designed to be comfortable to use, minimizing physical effort and fatigue. The physical design of the system should allow the user to maintain a natural posture with reasonable operating effort. Repetitive or sustained actions should be avoided.

7. Size and space for approach and use.

Appropriate size and space is provided for approach, reach, manipulation, and use regardless of the user’s body size, posture, or mobility. A flexible work area designed for use by employees who are left- or right-handed and have a variety of other physical characteristics and abilities is an example of applying this principle.

These seven principles give us a good starting point in considering universal design.

Multi-modal interaction

Providing access to information through more than one mode of interaction. Situation where the user is provided with multiple modes for interacting with the system. There are five senses, sight, sound, touch, taste and smell. A Multi-modal interface acts as a facilitator via these modes of interaction. Used in a range of applications: particularly good for users with special needs, and virtual reality. e.g. visual and aural senses: a text processor may speak the words as well as echoing them to the screen.

Sound in the interface

An important multi model interaction to usability. More widespread effective use of sound in the interface would alleviate the problems faced by visually impaired people. There are two types of sound that we could use,

  1. Speech - The term speech interface describes a software interface that employs either human speech or simulated human speech .Complexity of the language makes speech recognition and synthesis by computer very difficult.

e.g. The phonetic typewriter- The phonetic typewriter is the device which is to convert the human voice into typed letters. Though amplitudes, timbers, and durations of the speech wave coming into the ear are various, these speech sounds are changed into a definite letter set when the hands strike the keys of a typewriter. One reason that the phonetic typewriter was able to achieve acceptable levels of recognition and transcription is that Finnish is a phonetic language, that is one which is spelt as it sounds.

The phonetic typewriter

2.Non-speech -Non-speech sounds can offer a number of advantages. As speech is serial, we have to listen to most of a sentence before we understand what is being said. Non-speech sounds can often be assimilated much more quickly. Speech is language dependent- a speech-based system requires translation for it to be used for another language group. The meaning of non-speech sounds can be learned regardless of language. Speech requires the user’s attention. Non-speech sound can make use of the phenomenon of auditory adaptation: background sounds are ignored unless they change or cease. Commonly used for warnings and alarms. It is often used to provide transitory information, such as indications of network or system changes, or of errors. It can also be used to provide status information on background processes, since we are able to ignore continuous sounds but still respond to changes in those sounds. Non-speech sound can also be used to provide a second representation of actions and objects in the interface to support the visual mode and provide confirmation for the user.

Touch in the interface

Touch interface is where the users can interact with the machine using the sense of touch. Users can use their hands or a stylus to touch the screen when making selections on the machine. This interface much relies on graphical user interface(GUI) which allows user to see what they should touch when making a selections. In some cases of visual impairments, there is a level of interactions based upon tactile or braille input. Touch sensitive interfaces can be found on many mobile devices such as a smart phone or a tablet computer.

Handwriting recognition

Handwriting is another communication mechanism which we are used to in day-today life. Handwriting consists of complex strokes and spaces .Captured by digitizing tablet and strokes transformed to sequence of dots .Large tablets are suitable for digitizing maps and technical drawings. Smaller devices, some incorporating thin screens to display the information (PDAs such as Palm Pilot)

Gesture recognition

Gesture recognition is a type of perceptual computing user interface that allows computers to capture and interpret human gestures as commands. The general definition of gesture recognition is the ability of a computer to understand gestures and execute commands based on those gestures.

Designing Interfaces for diversity

Human capabilities are different needs and limitations. Normally interface is designed for average users. People are diverse, thus it is important to consider many factors when we want to apply universal design. Factors to consider;

  1. Disability
  2. Age
  3. Culture


visual impairment

These days, the standard interface is graphical. The use of this reduces the possibilities for them. We use following devices to help them.

Peripherals-screen readers, braille output, Sonic Finder

Sound-speech, earcons, auditory icons

Touch-tactile interaction, force feedback devices

hearing impairment

Less impact on graphical interface compared to visual impairment. Computers enhance communication opportunities for them.

text communication, gesture, captions

physical impairment

vary in control and movement abilities.

speech I/O, eyegaze system(track eye movements to control cursors), gesture, predictive systems (e.g. Reactive keyboard-anticipate the commands to be typed and executed)

speech impairment

speech synthesis, text communication


Difficulty with learning to read fluently

Severe-speech input, output

Non-severe-spelling correction facilities

Consistent navigation structure, clear signposting cues

Color coding information, graphical information


Impaired social interaction and verbal and non-verbal communication

Communication-computer-mediated communication, virtual environments, graphical information

Education-virtual environments, games for social situations and appropriate responses.

age groups

Older people e.g. disability aids, memory aids, communication tools to prevent social isolation.

children e.g. appropriate input/output devices, involvement in design process

cultural differences

influence of nationality, generation, gender, race, sexuality, class, religion, political persuasion etc. on interpretation of interface features ;

Language-translations, layouts(reading patterns)

Cultural symbols

Gestures-movement of bodies.

Use of colors-red(life- India, happiness-China, royalty-France),green(fertility-Egypt, youth-China, safety-USA)

Designers and users use their understanding, perspectives and experience in a variety of environments. The more we learn about people and the choices they may wish as they interact with the environments, the better we become. Because of this, no one knows it all. We can all learn from each other about how to better design things for all people.





Hansa Sandamal

Undergraduate Student | Bsc(Hons) Software Engineering | University of Kelaniya