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p.2 The human mind is exquisitely tailored to make sense of the world. Give it the slightest clue and off it goes, providing
explanation, rationalization, understanding... Well-designed objects are easy to interpret and understand. They contain visible
clues to their operation.
p.9 the term affordance refers to the perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used
p.13 A good conceptual model allows us to predict the effects of our actions. Without a good model we operate by rote, blindly; we do operations as we were told to do them; we can't fully appreciate why, what effects to expect, or what to do if things go wrong.
p.14 For everyday things, conceptual models need not be very complex.
p.27 Feedback - sending back to the user information about what action has actually been done, what result has been accomplished - is a well-known concept in the science of control and information theory.
p.49-50 For a surprisingly large number of everyday tasks, the difficulty resides entirely in deriving the relationships between the mental intentions and interpretations and the physical actions and states.
p.51 Does the system provide actions that correspond to the intentions of the person? ...Does the system provide a physical representation that can be directly perceived and that is directly interpretable in terms of the intentions and expectations of the person?
p.54-55 not all of the knowledge required for precise behavior has to be in the head. It can be distributed - partly in the head, partly in the world, and partly in the constraints of the world. Precise behavior can emerge from imprecise knowledge for four reasons.
1. Information is in the world... 2. Great precision is not required... 3. Natural constraints are present... 4. Cultural constraints are present...
Because of these natural and artificial constraints, the number of alternatives for any particular situation is reduced, as are the amount and specificity of knowledge required within human memory.
p.55 In everyday situations, behavior is determined by the combination of internal knowledge and external information and constraints. People routinely capitalize on this fact... People can deliberately organize their environment to support their behavior.
p.56 Whenever information needed to do a task is readily available in the world, the need for us to learn it diminishes.
p.57 People function through their use of two kinds of knowledge: knowledge of and knowledge how.
p.62 The constraints by themselves are often not sufficient to determine the proper reassembly of the device... but the constraints reduce the amount that must be learned to a reasonable quantity.
p.69 Part of the power of a good mental model lies in its ability to provide meaning to things... the appropriate interpretation may not at first be obvious; it, too, is knowledge and has to be discovered.
p.70 People are explanatory creatures... Explanations and interpretations of events are fundamental to human performance, both in understanding the world and in learning and remembering... Mental models simplify learning, in part because the details of the required behavior can be derived when needed. They can be invaluable in dealing with unexpected situations... Mental models let people derive appropriate behavior for situations that are not remembered (or never before encountered). People probably make up mental models for most of the things they do.
p.71 The power of mental models is that they let you figure out what would happen in novel situations. Or, if you are actually doing the task and there is a problem, they let you figure out what is happening.
p.74 I am waiting for the day when portable computers become small enough that I can keep one with me at all times. I will definitely put all my reminding burdens upon it. It has to be small. It has to be convenient to use... it will exist in imperfect form in five years, possibly in perfect form in ten.
p.79 Knowledge in the World
Retrievable whenever visible or audible... Learning not required. Interpretation substitutes for learning. How easy it is to interpret information in the world depends upon how well it exploits natural mappings and constraints... Tends to be slowed up by the need to find and interpret the external information... Ease of use at first encounter: High
p.80 Knowledge in the world acts as its own reminder.
p.81 The difficulty of dealing with novel situations is directly related to the number of possibilities.
p.82 When we encounter a novel object, how can we tell what to do with it? Either we have dealt with something similar in the past and transform old knowledge to the new object, or we obtain instruction. In these cases, the information we need is in the head. Another approach is to use information in the world, particularly if the design of the new object has presented us with information that can be interpreted... How can design signal the appropriate actions? ...One appropriate set of signals comes through the natural constraints of objects, physical constraints that limit what can be done. Another set of signals comes from the affordances of objects, which convey messages about their possible uses, actions, and functions... Affordances can signal how an object can be moved, what it will support... Affordances suggest the range of possibilities, constraints limit the number of of alternatives. The thoughtful use of affordances and constraints together in design lets a user determine readily the proper course of action, even in a novel situation.
p.87 When we approach a door, we have to find both the side that opens and the part to be manipulated; in other words,
we need to figure out what to do and where to do it. We expect to find some visible signal for the correct operation: a plate,
an extension, a hollow, an indentation - something that allows the hand to touch, grasp, turn or fit into. This tells us where
to act. The next step is to figure out how: we must determine what operations are permitted, in part using the affordances,
in part guided by constraints.
p.99 for knowing what to do there are other relevant principles, too, especially visibility and feedback:
1. Visibility. Make relevant parts visible.
2. Feedback. Give each action an immediate and obvious effect.
p.124 What are not everyday activities? Those with wide and deep structures, the ones that require considerable conscious planning and thought, deliberate trial and error: trying first this approach, then that - backtracking... intellectual games: bridge, chess, poker, crossword puzzles, and so on... In general, we find wide and deep structures in games and leisure activities, where the structure is devised so as to occupy the mind or to make the task deliberately (and artificially) difficult. After all, what challenge would there be if games such as chess or bridge were conceptually simple? [JLJ - it probably would make writing software to play the game a little easier]
p.125 Much human behavior is done subconsciously, without conscious awareness and not available to inspection... Subconscious thought... proceeds rapidly and automatically, without effort. Subconscious processing is one of our strengths.
p.140 There are lots of ways for a designer to deal with errors... Put the required knowledge in the world. Don't require all the knowledge to be in the head... Use the power of natural and artificial constraints: physical, logical, semantic, and cultural... Narrow the gulfs of execution and evaluation. Make things visible, both for execution and evaluation
p.145 Consider the typewriter keyboard... The current standard keyboard was designed by Charles Latham Sholes in the 1870s. The design was called the "qwerty" keyboard... or sometimes the Sholes keyboard... it eventually became the Remington typewriter, the model upon which most manual typewriters were constructed.
p.164 The ability of conscious attention is limited: focus on one thing and you reduce your attention to others. Psychologists call the phenomenon "selective attention." Excessive focus leads to a kind of tunnel vision, where peripheral items are ignored.
p.180 the best computer programs are the ones in which the computer itself "disappears," in which you work directly on the problem without having to be aware of the computer.
p.183-184 There are three requirements for a system to be explorable.
- In each state of the system, the user must readily see and be able to do the allowable actions. The visibility acts as a suggestion, reminding the user of possibilities and inviting the exploration of new ideas and methods.
- The effect of each action must be both visible and easy to interpret. This property allows users to learn the effects of each action, to develop a good mental model of the system, and to learn the causal relationships between actions and outcomes. The system image plays a critical role in making such learning possible.
- Actions should be without cost. When an action has an undesirable result, it must be readily reversible. This is especially important in computer systems... Most actions should be cost-free, explorable, discoverable.
p.188-189 Seven Principles for Transforming Difficult Tasks into Simple Ones
- Use both knowledge in the world and knowledge in the head.
- 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.
p.215 When I read an interesting article and store it away in my files for some unknown but probable future use, I know at the time I stick it away that I may never be able to remember where I put it.
p.240 My work has been heavily influenced by Simon, especially by his ideas developed in The sciences of the artificial (1981), which, among other things, points out that much of the complexity of our behavior reflects the complexity of the world, not of our thought processes. | 