The book is highly regarded introductory text to usability
and interaction design
. So, while
we're noding our homework
The Design of Everyday Things
(originally published as The Psychology of Everyday Things
Author: Don Norman
Chapter One: The Psychopathology of Everyday Things
The world is filled with objects that cannot be understood, with devices that lead to error. Things as simple as a door can, in the hands of an inept designer, become points of confusion and frustration for a user. Norman introduces several ideas core to the study of interfaces.
- Affordances, referring to the fundamental properties that determine how a given thing could possibly be used.
- Conceptual models refers to the mental models users develop to understand the operation of a device.
- Mapping, meaning the relationships people assign between two things, in this case the controller and the controlled.
- Feedback, the information sent to the user confirming
that has been done or describing the result of an action.
Chapter Two: The Psychology of Everyday Actions
People tend to blame themselves for mistakes made with interfaces, but they are rarely to blame. People can incorrectly attribute causes & effects when not provided feedback, by creating a faulty conceptual model.
When people fail at a task repeatedly, they may blame themselves and give up, a condition termed learned helplessness
. When paced situations require that a user fully master one set of tasks before moving to the next, users that fall behind stay behind for the rest of the situation. People may inappropriately attribute their failure to a general inability. This is called taught helplessness
Questions for the designer:
The Seven Stages of Action
(How easily can the user...)
- Forming the goal (Determine the function of the device?)
- Forming the intention (Tell what actions are possible?)
- Specifying an action (Determine mapping from intention to physical movement?)
- Executing an action (Perform the action?)
- Perceiving the state of the world (Tell what state the system is in?)
- Interpreting the state of the world (Determine mapping from system state to interpretation?)
- Evaluating the outcome (Tell if the system is in the
When a person cannot determine what actions produce the desired result, a gulf of execution
is created that prevents them from accomplishing their goal. How much work a person must do to determine if their actions have had the desired result is termed the gulf of evaluation
. Designers should work to narrow these gulfs.
Chapters one and two tell us that designers should provide:
- Good conceptual models
- Good mappings
Chapter Three: Knowledge in the Head and in the World
Human knowledge and memory can be faulty in nature. This does not always hinder actions, for one of four reasons:
- Information is in the world. People don't need to remember how. They can look to see.
- Great precision is not required. People don't need to remember all details, just major details.
- Natural constraints are present. You simply can not perform the wrong action.
- Cultural constraints are present. People memorize standards for the action.
has three categories.
- Memory for arbitrary things Memorization
- Memory for meaningful relationships Analogy
- Memory through explanations Derivation from known principles
The two aspects to a reminder (information in the world) are the signal
and the message. Natural mappings
reduce the need for people to keep information about how to act in memory. Natural mappings
associate the signal to the message visually.
Designers must appropriately choose when to rely on user's memory and when to use instructions/reminders, recognizing the tradeoffs of each in terms of retrievability, need for learning, efficiency of use, ease of initial use, and aesthetics.
Chapter Four: Knowing What to Do
The difficulty of dealing with novel situations directly related to the number of possibilities. The number of allowable actions depends on constraints:
- Physical constraints This action is the only action you can do.
- Semantic constraints This is the only action which would have meaning to the desired outcome.
- Cultural constraints This is what I've seen everywhere else.
- Logical constraints Inductive or deductive options.
Norman provides extensive examples with doors.
Designers can reduce the number of allowable actions with applied constraints, meaningful mapping and careful arrangement of control devices.
Visibility and feedback are vital to users' knowing what to do in a novel situation. Designers should make system states and controls visible using displays and/or sounds.
Chapter Five: To Err is Human
Errors can be categorized as/when:
- Capture errors/A frequently done task takes over a less frequently done task.
- Description errors/Components necessary for the task are confused with similar ones.
- Data-driven errors/Observed data substitutes for correct data.
- Associative activation errors/Automated responses to similar activations are confused.
- Loss-of-activation errors/The goal for a series of actions is forgotten.
- Mode errors/An action appropriate for different situations is used.
can sometimes be difficult to detect. Without feedback, errors that occur in a complex series of tasks can be difficult to determine.
Norman describes some models of human thought, focusing on the connectionist approach. He describes memory as a multiple-exposure to experiences, from which people derive archetypal experiences. New experiences will be remembered and responded to as similar to the archetype or very dissimilar from the archetype. This tendency affects the structure of tasks.
Decision trees for a task can characterize the task as wide or narrow, and shallow or deep. More available options make a task wider. More subsequent, dependent options make a task deeper. Most everyday tasks are narrow and/or shallow. Tasks that are wide and/or deep are considered unusual and difficult. In general, wide and deep tasks are found in games and leisure activities in which we challenge ourselves to the difficult task.
Subconscious thought is quick and effortless, and good at finding patterns. Conscious thought is slow and deliberate, considering options for novel situations. Both are subject to errors. Conscious thought is severely limited by the capacity to short term memory, which can hold at any one time five or six items.
Mistakes may seem quite reasonable to the person making them. Mistakes may be difficult to detect. Social pressure may pressure people into making mistakes or more readily explain away mistakes.
Forcing functions are physical constraints that include interlocks, lockins, and lockouts.
- Interlocks force operations to take place in the proper sequence.
- Lockins keep an operation active until other actions occur.
- Lockouts prevent an event from occurring.
Designers must consider how errors will affect their system and how users will recover from errors. They should:
- Understand the causes of error and design to minimize those causes.
- Make it possible to reverse actions—to undo them—or make it harder to do what cannot be reversed.
- Make it easy to discover the errors that do occur, and make them easy to correct.
- Change attitude toward errors: People aren't doing something that's wrong, they are approximations of what is desired.
- Put the required knowledge in the world-rather than rely on the users' memory-without hindering advanced users.
- Use the power of constraints, forcing functions and natural mappings.
- Narrow the gulfs of execution and evaluation.
Chapter Six: The Design Challenge
Pressures of time, uniqueness demands, client demands, and economic limitations hinder the positive evolutions of design. Norman uses the evolution of the typewriter key layout as an example. User testing can overcome these problems.
Everyone involved in the design process should understand:
- Designers are not typical users.
- Clients are not typical users.
- Corporate purchasers may not be typical users.
Designers can overcome problems of user variance by making systems customizable.
Designers should guard against selective focus in their own designs: Were the decisions made for reasons that caused them to neglect others?
Norman uses the faucet as an example of selective focus.
Designers hoping to ensure usability should avoid two temptations.
- Creeping featurism - The desire to impress users with extensive functionality.
- The worshipping of false images. Users that purchase products for reasons other than usability.
Norman criticizes computer systems in light of usability
principles. (It should be noted that he was largely describing DOS
-based systems of 1988 rather than the Macintosh
OS or Windows
-95 and later OS
in use today.)
The computer is completely customizable. Designers of computer systems should:
- Invite experimentation by the user.
- Apply direct manipulation when the task is critical, novel, or ill-specified.
- Apply indirect manipulation tools where tasks are laborious or repetitive.
- Norman offers conjecture about the computers of (1988's) future.
Chapter Seven: User-Centered Design
Design should make sure that the user can figure out what to do and what is going on by:
- Make it easy to determine what actions are possible at any moment, making use of constraints.
- Make things visible, including the conceptual model of the system, the alternative actions, and the results of actions.
- Make it easy to evaluate the state of the system.
- Follow natural mappings between intentions and the required actions; between actions and the resulting effect; and between the information that is visible and the interpretation of the system state.
- Use both knowledge in the head and knowledge in the world.
- Simplify the structure of tasks.
- Make things visible: bridge the gulfs of Execution and Evaluation.
- Get the mappings right.
- Exploit the power of constraints, both natural and artificial.
- Design for error.
- When all else fails, standardize.
Users do not read manuals
. They cannot be counted on.
When simplifying the structure of complex tasks, the designer can:
- Keep the task the same, but provide mental aids.
- Use technology to make visible what would otherwise be invisible, improving feedback and ability to keep control.
- Automate, leaving the task the same.
- Change the nature of the task.
Designers can intentionally discourage certain actions by making the tasks more complex or difficult.
Norman discusses examples of how method-enabled by technology-affects outcome in writing, reading, and living in our homes, and makes a call to action for designers to design responsibly.