Design of Everyday Things [34]
Each point provides support for one or more of the seven stages of action. The next time you can’t immediately figure out the shower control in a motel or work an unfamiliar television set or stove, remember that the problem is in the design. And the next time you pick up an unfamiliar object and use it smoothly and effortlessly on the first try, stop and examine it: the ease of use did not come about by accident. Someone designed the object carefully and well.
CHAPTER THREE
KNOWLEDGE IN THE HEAD AND IN THE WORLD
A friend kindly let me borrow his car. Just before I was about to leave, I found a note waiting for me: “I should have mentioned that to get the key out of the ignition the car needs to be in reverse.”
The car needs to be in reverse! If I hadn’t seen the note, I never could have figured that out. There was no visible cue in the car: the knowledge needed for this trick had to reside in the head. If the driver lacks that knowledge, the key stays in the ignition forever.
It is easy to show the faulty nature of human knowledge and memory. A common classroom exercise in the United States demonstrates that students cannot recall the pairing of letters and numbers on their telephones. One of my graduate students found that when professional typists were given caps for typewriter keys, they could not arrange them in the proper configuration.1 American students dial telephones properly, and all those typists could type rapidly and accurately. Why the apparent discrepancy between the precision of behavior and the imprecision of knowledge? Because 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. Much of the information a person needs to do a task can reside in the world. Behavior is determined by combining the information in memory (in the head) with that in the world.
2. Great precision is not required. Precision, accuracy, and completeness of knowledge are seldom required. Perfect behavior will result if the knowledge describes the information or behavior sufficiently to distinguish the correct choice from all others.
3. Natural constraints are present. The world restricts the allowed behavior. The physical properties of objects constrain possible operations: the order in which parts can go together and the ways in which an object can be moved, picked up, or otherwise manipulated. Each object has physical features—projections, depressions, screwthreads, appendages—that limit its relationships to other objects, operations that can be performed to it, what can be attached to it, and so on.
4. Cultural constraints are present. In addition to natural, physical constraints, society has evolved numerous artificial conventions that govern acceptable social behavior. These cultural conventions have to be learned, but once learned they apply to a wide variety of circumstances.
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.
In everyday situations, behavior is determined by the combination of internal knowledge and external information and constraints. People routinely capitalize on this fact. They can minimize the amount of material they must learn or the completeness, precision, accuracy, or depth of the learning. People can deliberately organize the environment to support their behavior. Some people with brain damage can function so well that even their co-workers may not be aware of their handicap. Nonreaders have been known to fool others, even in situations where their job presumably requires reading skills. They know what is expected of them, follow the behavior of their co-workers, and set up situations so that they do not need to