Sneak Previews of Forthcoming Books of Special Interest to Southern Californians : Mental Life Is Not Neat and Orderly

The following is from “The Psychology of Everyday Things,” by Donald A. Norman, to be published in May.

PSYCHOLOGISTS HAVE chronicled the failure of thought, the non-rationality of real behavior. Even simple tasks can sometimes throw otherwise clever people into disarray. Even though principles of rationality seem as often violated as followed, we still cling to the notion that human thought should be rational, logical and orderly. Much of law is based on the concept of rational thought and behavior. Much of economic theory is based on the model of the rational human who attempts to optimize personal benefit, utility or comfort. Many scientists who study artificial intelligence use the mathematics of formal logic--the predicate calculus--as their major tool to stimulate thought.

But human thought--and its close relatives, problem-solving and planning--seems more rooted in past experience than in logical deduction. Mental life is not neat and orderly. It does not proceed smoothly and gracefully in neat, logical form. Instead, it hops, skips and jumps its way from idea to idea, tying together things that have no business being put together; forming new creative leaps, new insights and concepts. Human thought is not like logic; it is fundamentally different in kind and in spirit. The difference is neither worse nor better. But it is the difference that leads to creative discovery and to great robustness of behavior.

Thought and memory are closely related, for thought relies heavily on the experiences of life. Indeed, much problem-solving and decision-making takes place through attempts to remember some previous experience that can serve as a guide for the present. There have been many theories of human memory. For example, every method of filing things has shown up somewhere along the line as a model for human memory. Do you file photographs neatly in a scrapbook? One theory of memory has postulated that our experiences are neatly encoded and organized, as if in a photo album. This theory is wrong. Human memory is most definitely not like a set of photographs or a tape recording. It mushes things together too much, confuses one event with another, combines different events and leaves out parts of individual events.

Another theory is based on the filing-cabinet model, wherein there are lots of cross references and pointers to other records. This theory has a good deal going for it, and it is probably a reasonable characterization of the most prominent approach today. Of course, it is not called a file-cabinet theory. It goes by the names of “schema theory,” “frame theory,” sometimes “semantic networks” and “propositional encoding.” The individual file folders are defined in the formal structure of the schemas or frames, and the connections and associations among the individual records make the structure into a vast and complex network. The essence of the theory consists of three beliefs, all reasonable and supported by considerable evidence: that there is logic and order to the individual structures (this is what the schema or frame is about); that human memory is associative, with each schema pointing and referring to multiple others to which it is related or that help define the components (thus the term “network”), and that much of our power for deductive thought comes from using the information in one schema to deduce the properties of another (thus the term “propositional encoding”). To illustrate the third concept: Once I learn that all living animals breathe, I know that any live animal I will ever meet will breathe. I don’t have to learn this separately for all animals. We call this the “default value.” Unless told otherwise, anything I learn for a general concept applies to all of its instances by default. Default values do not have to apply to everything--I can learn exceptions, such as that all birds fly except for penguins and ostriches. But defaults hold true unless an exception shows otherwise. Deduction is a most useful and powerful property of human memory.

IF I WERE placed in the cockpit of a modern jet airliner, my inability to perform gracefully and smoothly would neither surprise nor bother me. But I shouldn’t have trouble with doors and switches, water faucets and stoves. “Doors?” I can hear the reader saying. “You have trouble opening doors?” Yes. I push doors that are meant to be pulled, pull doors that should be pushed and walk into doors that should be slid. Moreover, I see others having the same troubles--unnecessary troubles. There are psychological principles that can be followed to make these things understandable and usable.

Consider the door. There is not much you can do to a door: You can open it or shut it. Suppose you are in an office building, walking down a corridor. You come to a door. In which direction does it open? Should you pull or push, on the left or the right? Maybe the door slides. If so, in which direction? I have seen doors that slide up into the ceiling. A door poses only two essential questions: In which direction does it move? On which side should one work it? The answers should be given by the design, without any need for words or symbols, certainly without any need for trial and error.

A friend told me of the time he got trapped in the doorway of a post office in a European city. The entrance was an imposing row of perhaps six glass swinging doors, followed immediately by a second, identical row. That’s a standard design: It helps reduce the airflow and thus maintain the indoor temperature of the building.

My friend pushed on the side of one of the leftmost pair of outer doors. It swung inward, and he entered the building. Then, before he could get to the next row of doors, he was distracted and turned around for an instant. He didn’t realize it at the time, but he had moved slightly to the right. So when he came to the next door and pushed it, nothing happened. “Hmm,” he thought, “must be locked.” So he pushed the side of the adjacent door. Nothing. Puzzled, my friend decided to go outside again. He turned around and pushed against the side of a door. Nothing. He pushed the adjacent door. Nothing. The door he had just entered no longer worked. He turned around once more and tried the inside doors again. Nothing. Concern, then mild panic. He was trapped! Just then, a group of people on the other side of the entryway (to my friend’s right) passed easily through both sets of doors. My friend hurried over to follow their path.

How could such a thing happen? A swinging door has two sides. One contains the supporting pillar and the hinge, the other is unsupported. To open the door, you must push on the unsupported edge. If you push on the hinge side, nothing happens. In this case, the designer aimed for beauty, not utility. No distracting lines, no visible pillars, no visible hinges. So how can the ordinary user know which side to push on? While distracted, my friend had moved toward the (invisible) supporting pillar, so he was pushing the doors on the hinged side. No wonder nothing happened. Pretty doors. Elegant. Probably won a design prize.

The door story illustrates one of the most important principles of design: visibility. The correct parts must be visible and must convey the correct message. With doors that push, the designer must provide signals that naturally indicate where to push. These need not destroy the aesthetics. Put a vertical plate on the side to be pushed, nothing on the other. Or make the supporting pillars visible. The vertical plate and supporting pillars are natural signals, naturally interpreted, without any need to be conscious of them. I call the use of natural signals “natural design.”

Copyright 1988 by Donald A. Norman. Reprinted by permission of Basic Books, Inc., Publishers, New York.