Design of Everyday Things [47]
A major problem is that often the purchaser is not the user. Appliances may be in a home when people move in. In the office, the purchasing department orders equipment based upon such factors as price, personal relationships with the supplier, and perhaps reliability: usability is seldom considered. Finally, even when the purchaser is the end user, it is sometimes necessary to trade one desirable feature for an undesirable one. In the case of my family’s stove, we did not like the arrangement of controls, but we bought the stove anyway: we traded off layout of the burner controls for another feature that was more important to us and available only from one manufacturer. (I return to these issues in chapter 6.)
The Tradeoff between Knowledge in the World and in the Head
Knowledge (or information) in the world and in the head are both essential in our daily functioning. But to some extent we can choose to lean more heavily on one or the other. That choice requires a trade off—gaining the advantages of knowledge in the world means losing the advantages of knowledge in the head (figure 3.6).
3.6 Tradeoffs
PROPERTYKNOWLEDGE IN THE WORLDKNOWLEDGE IN THE HEAD
Retrievability Retrievable whenever visible or audible. Not readily retrievable. Requires memory search or reminding.
Learning 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. Requires learning, which can be considerable. Learning is made easier if there is meaning of structure to the material (or if there is a good mental model).
Efficiency of use Tends to be slowed up by the need to find and interpret the external information. Can be very efficient.
Ease of use at first encounter High. Low.
Aesthetics Can be unaesthetic and inelegant, especially if there is a need to maintain a lot of information. This can lead to clutter. In the end, aesthetic appeal depends upon the skill of the designer. Nothing need be visible, which gives more freedom to the designer, which in turn can lead to better aesthetics.
Knowledge in the world acts as its own reminder. It can help us recover structures that we otherwise would forget. Knowledge in the head is efficient: no search and interpretation of the environment is required. In order to use knowledge in the head we have to get it there, which might require considerable amounts of learning. Knowledge in the world is easier to learn, but often more difficult to use. And it relies heavily upon the continued physical presence of the information; change the environment and the information is changed. Performance relies upon the physical presence of the task environment.
Reminders provide a good example of the relative tradeoffs between the roles of internal versus external knowledge. Knowledge in the world is accessible. It is self-reminding. It is always there, waiting to be seen, waiting to be used. That is why we structure our offices and our places of work so carefully. We put piles of papers where they can be seen, or if we like a clean desk, we put them in standardized locations and teach ourselves (knowledge in the head) to look in these standard places routinely. We use clocks and calendars and notes. Knowledge in the mind is ephemeral: here now, gone later. We can’t count on something being present in mind at any particular time, unless it is triggered by some external event or unless we deliberately keep it in mind through constant repetition (which then prevents us from having other conscious thoughts).