Design of Everyday Things - Norman, Don [35]
Precise Behavior from Imprecise Knowledge
INFORMATION IS IN THE WORLD
Whenever information needed to do a task is readily available in the world, the need for us to learn it diminishes. For example, we lack knowledge about common coins, even though we recognize them just fine (figure 3.1). Or consider typing. Many typists have not memorized the keyboard. Usually each letter is labeled, so nontypists can hunt and peck letter by letter, relying on knowledge in the world and minimizing the time required for learning. The problem is that such typing is slow and difficult. With experience, of course, hunt-and-peck typists learn the positions of many of the letters on the keyboard, even without instruction, and typing speed increases notably, quickly surpassing handwriting speeds and, for some, reaching quite respectable rates. Peripheral vision and the feel of the keyboard provide some information about key locations. Frequently used keys become completely learned, infrequently used keys are not learned well, and the other keys are partially learned. But as long as the typist needs to watch the keyboard, the speed is limited. The knowledge is still mostly in the world, not in the head.
If a person needs to type large amounts of material regularly, further investment is worthwhile: a course, a book, or an interactive computer program. The important thing is to learn the proper placement of fingers on the keyboard, to learn to type without looking, to get knowledge about the keyboard from the world into the head. It takes several hours to learn the system and several months to become expert. But the payoff of all this effort is increased typing speed, increased accuracy, and decreased mental load and effort at the time of typing.
There is a tradeoff between speed and quality of performance and mental effort. Thus, in finding your way through a city, locating items in a store or house, or working complex machinery, the tradeoff can determine what needs to be learned. Because you know that the infor-mation is available in the environment, the information you internally code in memory need be precise enough only to sustain the quality of behavior you desire. This is one reason people can function well in their environment and still be unable to describe what they do. For example, a person can travel accurately through a city without being able to describe the route precisely.
3.1 Which Is the U. S. One Cent Coin—The Penny? Fewer than half of the American college students who were given this set of drawings and asked to select the correct one could do so. Pretty bad performance, except that the students, of course, have no difficulty using the money: in normal life, we have to distinguish between the penny and other U.S. coins, not between several versions of one denomination. (From Nickerson & Adams, Cognitive Psychology, 11, © 1979. Reprinted by permission of Academic Press.)
People function through their use of two kinds of knowledge: knowledge of and knowledge how. Knowledge of—what psychologists call declarative knowledge—includes the knowledge of facts and rules. “Stop at red lights.” “New York City lies on a parallel a bit south of Madrid, San Diego’s longitude is east of Reno.” “To get the key out of the ignition, the car must be in reverse.” Declarative knowledge is easy to write down and to teach. Knowledge how—what psychologists call procedural knowledge—is the knowledge that enables a person to perform music, to stop a car smoothly with a flat tire on an icy road, to return a serve in tennis, or to move the tongue properly when saying the phrase “frightening witches.” Procedural knowledge is difficult or impossible to write down and difficult to teach. It is best taught