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Developed by Tim Bell

Department of Computer Science and Software Engineering

University of Canterbury

tim.bell@canterbury.ac.nz

Human Computer Interaction

An introduction to HCI Heuristics for NZQA achievement standard AS91371 (2.44)

Licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 License

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References

Usability Engineering (Jakob Nielson)

Designing with the mind in mind (Johnson)

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HCI perspective on a system

User

Device

interface

System

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It is easy to think of a digital system as an entity in itself, but really the actual system involves a user who uses a device through a user interface. The system that has to work well is everything inside the box. A computer scientist needs to understand all those parts of the system, and not just the device. The study of Human Computer Interaction involves a lot of psychology (how people behave) because this affects how they will use a system. As a simple example, human short term memory is typically around 8 seconds. If a device delays for more than 8 seconds, the user has to make a conscious effort to remember what they were doing, and that’s extra work for the user (from their point of view, the system is more tiring to use). Another example (used later on) is that people are better at recognising things than remembering them.

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Are users dummies?

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Human-computer interaction, usability

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Heuristics (Nielson)

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Examples illustrating heuristics

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Looking at examples is a good way to sensitise students to the kinds of issues that can be commented on. We have provided some examples in the following slides, but teachers are encouraged to substitute examples from their own experience. Many of them are humorous, but some have serious consequences (including deleting important files or booking a flight for the wrong day). There are other examples not used here where bad interface design has led to loss of life e.g. in aircraft controls, but the emphasis here is differentiating between adequate designs that do the job, and great designs where the user feels empowered by the interface rather than frustrated. Many of the problems students find might be relatively minor, but bear in mind that millions of people might experience the small frustration from that small problem, or a few people might have to experience those frustrations many times each day as they do their work.

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Visibility of system status

The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.

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Feedback – reasonable time

1/10 second: instant
1 second: interactive
10 seconds: need an indicator

HCI for level 2 Computer Science

What is a reasonable amount of time for this heuristic? For humans, the above time scales are “reasonable” (this is discussed in Johnson’s book).

If computer responds in about 1/10^th of a second (e.g. clicking on a checkbox and it activates) it will appear to be instant, and if it takes longer, it may seem that it hasn’t activated and the user will click it again, usually leading to confusion because in the real world we’re used to instant response (e.g. you turning on a tap or switching on a light).

Around 1 second is what people are used to in conversation, so if a series of interactions suddenly has a delay of more than 1 second (maybe while a disk is starting up or a large image is loading in a web page) it can throw the user’s train of thought, much like an interrupted conversation.

Around 8 seconds is the length of short-term memory, so systems that take longer than 10 seconds to respond need to keep the user informed about what is happening, usually with a progress indicator, which ideally should indicate how long the process will take.

The speed of feedback is one of the strong motivators for knowing about fast algorithms (which was covered in AS91074/1.44); if one algorithm takes 2 seconds to sort a list and another takes 1 second, the latter is going to seem a lot more interactive; and if another takes 1/10^th of a second, the user will perceive that the system couldn’t be faster.

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Match between system and real world

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

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Match between system and real world

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Match between system and real world

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User control and freedom

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

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User control and freedom

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User control and freedom

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Consistency and standards

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

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Error prevention

Even better than good error messages is a careful design which prevents a problem from occurring in the first place. Either eliminate error-prone conditions or check for them and present users with a confirmation option before they commit to the action.

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Error prevention

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Error prevention

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Error prevention

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Combinations of issues

Error prevention
Match between system and real world
Consistency

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Recognition rather than recall

Minimize the user's memory load by making objects, actions, and options visible. The user should not have to remember information from one part of the dialogue to another. Instructions for use of the system should be visible or easily retrievable whenever appropriate.

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Flexibility and efficiency of use

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

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Aesthetic and minimalist design

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

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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.

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Help users recognize, diagnose, and recover from errors

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Help users recognize, diagnose, and recover from errors

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Help users recognize, diagnose, and recover from errors

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Help users recognize, diagnose, and recover from errors

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Help and documentation

Even though it is better if the system can be used without documentation, it may be necessary to provide 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.

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Help and documentation

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