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Two of the most important characteristics of good design are discoverability and understanding.
Design is concerned with how things work, how they are controlled, and the nature of the interaction between people and technology.
It is the duty of machines and those who design them to understand people. It is not our duty to understand the arbitrary, meaningless dictates of machines.
The solution is human-centered design (HCD), an approach that puts human needs, capabilities, and behavior first, then designs to accommodate those needs, capabilities, and ways of behaving.
Designers need to focus their attention on the cases where things go wrong, not just on when things work as planned.
Experience is critical, for it determines how fondly people remember their interactions.
Discoverability results from appropriate application of five fundamental psychological concepts covered in the next few chapters: affordances, signifiers, constraints, mappings, and feedback.
there is a sixth principle, perhaps most important of all: the conceptual model of the system.
An affordance is a relationship between the properties of an object and the capabilities of the agent that determine just how the object could possibly be used.
The presence of an affordance is jointly determined by the qualities of the object and the abilities of the agent that is interacting. This relational definition of affordance gives considerable difficulty to many people. We are used to thinking that properties are associated with objects. But affordance is not a property. An affordance is a relationship. Whether an affordance exists depends upon the properties of both the object and the agent.
To be effective, affordances and anti-affordances have to be discoverable—perceivable.
Affordances exist even if they are not visible. For designers, their visibility is critical:
Affordances determine what actions are possible. Signifiers communicate where the action should take place. We need both.
What people need, and what designers must provide, are signifiers.
Good design requires, among other things, good communication of the purpose, structure, and operation of the device to the people who use it. That is the role of the signifier.
related controls should be grouped together. Controls should be close to the item being controlled.
A device is easy to use when the set of possible actions is visible, when the controls and displays exploit natural mappings.
A conceptual model is an explanation, usually highly simplified, of how something works. It doesn’t have to be complete or even accurate as long as it is useful.
No matter how brilliant the product, if people cannot use it, it will receive poor reviews.
“People don’t want to buy a quarter-inch drill. They want a quarter-inch hole!”
Cognition attempts to make sense of the world: emotion assigns value.
Cognition provides understanding: emotion provides value judgments.
Feedback is critical to managing expectations, and good design provides this. Feedback—knowledge of results—is how expectations are resolved and is critical to learning and the development of skilled behavior.
DESIGN MUST TAKE PLACE AT ALL LEVELS: VISCERAL, BEHAVIORAL, AND REFLECTIVE
Well-designed devices can induce pride and enjoyment, a feeling of being in control and pleasure—possibly even love and attachment.
All three levels of processing work together to determine a person’s cognitive and emotional state. High-level reflective cognition can trigger lower-level emotions. Lower-level emotions can trigger higher-level reflective cognition.
Conceptual models are a form of story, resulting from our predisposition to find explanations.
everyone forms stories (conceptual models) to explain what they have observed.
people will use their own conceptual models of the world to determine the perceived causal relationship between the thing being blamed and the result.
Do not blame people when they fail to use your products properly.
Take people’s difficulties as signifiers of where the product can be improved.
Eliminate all error messages from electronic or computer systems. Instead, provide help and guidance.
Make it possible to correct problems directly from help and guidance messages. Allow people to continue with their task: Don’t impede progress—help make it smooth and continuous. Never make people start over.
Assume that what people have done is partially correct, so if it is inappropriate, provide the guidance that allows them to correct the problem and be on their way.
Think positively, for yourself and for the people you interact with.
human error usually is a result of poor design: it should be called system error.
Humans err continually; it is an intrinsic part of our nature. System design should take this into account.
Eliminate the term human error. Instead, talk about communication and interaction: what we call an error is usually bad communication or interaction.
The information that helps answer questions of execution (doing) is feedforward.
Feedforward is accomplished through appropriate use of signifiers, constraints, and mappings.
To maximize efficiency of working memory it is best to present different information over different modalities: sight, sound, touch (haptics), hearing, spatial location, and gestures.
strings of digits can be remembered if they can be associated with meaningful structures.
The design implications are clear: provide meaningful structures. Perhaps a better way is to make memory unnecessary: put the required information in the world. This is the power of the traditional graphical user interface with its old-fashioned menu structure. When in doubt, one could always examine all the menu items until the desired one was found.
The most effective way of helping people remember is to make it unnecessary.
The easier it is to enter the information into the relevant equipment as it is heard, the less chance of memory error.
Just as in doing an action we can distinguish between knowing what can be done and knowing how to do it, in reminding we must distinguish between the signal—knowing that something is to be remembered, and the message—remembering the information itself.
The ideal reminder has to have both components: the signal that something is to be remembered, and then the message of what it is.
Knowledge in the world includes perceived affordances and signifiers, the mappings between the parts that appear to be controls or places to manipulate and the resulting actions, and the physical constraints that limit what can be done.
Knowledge in the head includes conceptual models; cultural, semantic, and logical constraints on behavior; and analogies between the current situation and previous experiences with other situations.
