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`APPLE 1032
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`THE
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`PSYCHOLOGY
`
`OF EVERYDAY
`
`THINGS
`
`Donald A. Norman
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`# BasicBooks
`A Division of HarperCollinsPublishers
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`2
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`CHAPTER ONE
`
`THE
`
`PSYCHOPATHOLOGY
`
`OF EVERYDAY
`
`THINGS
`
`nak
`
`e
`
`“Kenneth Olsen, the engineer who founded and
`still runs Digital Equipment Corp., confessed at
`the annual meeting that he can’t figure out how to
`heata cup of coffee in the company’s microwave
`oven, “1
`
`You Would Need an Engineering Degree
`to Figure This Out
`
`“You would need an engineering degree from MIT to workthis,”
`someoneonce told me, shaking his head in puzzlement over his brand
`new digital watch. Well,
`I have an engineering degree from MIT.
`(Kenneth Olsen has two of them,and hecan’t figure out a microwave
`oven.) Give me a few hours and I can figure out the watch. But why ,
`should it take hours? I have talked with many people whocan’tuse all
`the features of their washing machines or cameras, whocan’tfigure out
`how to work a sewing machine or a video cassette recorder, who
`habitually turn on the wrong stove burner.
`Whydo weput up with the frustrations of everyday objects, with
`objects that we can’t figure out how to use, with those neatplastic-
`wrapped packages that seem impossible to open, with doors that trap
`people, with washing machines and dryers that have become too con-
`
`4
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`*
`
`sion of theartist.
`
`1.1 Carelman’s Coffeepot for Maso-
`chists. The French artist Jacques Carel-
`man in his series of books Catalogue
`d objets introuvables (Catalog of unfindable ob-
`jects) provides delightful examples of
`everyday things that are deliberately
`unworkable, outrageous, or otherwise
`ill-formed. Jacques Carelman: “Cof-
`feepot for Masochists.” Copyright ©
`1969-76-80 by Jacques Carelman and
`A.D.A.G.P.Paris. From Jacques Carel-
`man, Catalog of Unfindable Objects, Balland,
`éditeur, Paris-France. Used by permis-
`
`fusing to use, with audio-stereo-television-video-cassette-recorders
`that claim in their advertisements to do everything, but that make it
`almost impossible to do anything?
`The human mindis exquisitely tailored to make sense of the world.
`Giveit the slightest clue and off it goes, providing explanation,ration-
`alization, understanding. Consider the objects—books, radios, kitchen
`appliances, office machines, andlight switches—that make up our ev-
`eryday lives. Well-designed objects are easy to interpret and under-
`stand. They contain visible clues to their operation. Poorly designed
`objects can be difficult and frustrating to use. They provide no clues—
`or sometimes false clues. They trap the user and thwart the normal
`process of
`interpretation and understanding. Alas, poor design
`predominates. Theresult is a world filled with frustration, with objects
`that cannot be understood, with devices that lead to error. This book
`is an attempt to changethings.
`
`The Frustrations
`
`of Everyday Life opening doors?” Yes. I push doors that are meant to be pulled, pull
`
`doors that should be pushed, and walk into doors that shouldbe slid.
`Moreover, I see others having the same troubles—unnecessary trou-
`bles. There are psychological principles that can be followed to make
`these things understandable and usable.
`Consider the door. There is not much you can doto a door: you can
`openit or shut it. Suppose youare 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 doorslides. If so,
`in which direction? I have seen doors thatslide up into theceiling. A
`door poses only two essential questions: In which direction does it
`move? On which side should one workit? The answers should be given
`by the design, without any need for words or symbols, certainly with-
`out any need fortrial anderror.
`K Gu-}evetabal
`oy apt
`A friend told meofthe time he got trapped in the doorway ofa post
`office in a European city. The entrance was an imposing row ofperhaps »
`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.
`Myfriend pushed on theside of one of the leftmost pair of outer
`doors. It swung inward, and heentered the building. Then, before he
`couldget to the next row ofdoors, he was distracted and turned around
`for aninstant. He didn’t realizeit at the time, but he had moved slightly
`to the right. So when he cameto 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 andpushed against the side ofa door.
`Nothing. He pushed the adjacent door. Nothing. The door he hadjust
`entered no longer worked. He turned around once more andtried the
`inside doors again. Nothing. Concern, then mildpanic. He was trapped!
`Just then, a group ofpeople on the other side of the entranceway(to
`my friend’s right) passed easily through both sets of doors. My friend
`hurried over to follow their path.
`Howcould such a thing happen? A swinging door has twosides.
`Onecontains the supporting pillar and the hinge, the other is unsup-
`ported. 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, notutility. No distracting lines, no visible pillars, no
`visible hinges. So how can the ordinary user know which side to push
`
`one: The Psychopathology of Everyday Things
`
`+
`
`go"
`os
`
`2
`
`The Psychology of Everyday Things
`
`“3 If I were placed in the cockpit of a modern jet airliner, myinability to
`perform gracefully and smoothly wouldneither 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
`
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`1.2 A Row of Swinging Glass Doors in a Boston Hotel. A similar problem to
`the doors from that European post office. On which side of the door should you
`push? WhenI asked people whohad just used the doors, most couldn’t say. Yet
`only a few of the people I watched hadtrouble with the doors. The designers had
`incorporated a subtle clue into the design. Note that the horizontal bars are not
`centered: theyarea bit closer together on the sides you should push on. The design
`almost works—butnotentirely, for not everyone used the doorsright onthefirst
`try.
`
`on? While distracted, my friend had moved toward the (invisible)
`supportingpillar, so he was pushing the doors on the hinged side. No
`wonder nothing happened. Pretty doors. Elegant. Probably won a de-
`sign prize.
`
`The doorstory illustrates one of the most importantprinciples of
`design:isibility. The correct parts must be visible, and they must con-
`vey 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 supportingpillars are natural signals, naturally inter-
`preted, without any need to be conscious of them.I call the use of
`natural signals naturaldesign and elaborate on the approach throughout
`this book.
`
`Visibility problems come in many forms. Myfriend, trapped be-
`tween theglass doors, suffered from a lack of clues that would indicate
`whatpart of a door should be operated. Other problems concern the
`ings
`between what you wantto do and whatappears to be possible,
`“another topic that will be expanded upon throughout the book. Con-
`sider one type ofslide projector. This projector has a single button to
`control whethertheslide tray moves forward or backward. Onebutton
`to do two things? Whatis the mapping? Howcan youfigure out how
`to control the slides? You can’t. Nothingis visible to give the slightest
`hint. Here is what happenedto mein one of the many unfamiliar places
`I’ve lectured in during my travels as a professor:
`
`TheLeitz slide projectorillustrated in figure 1.3 has shown up sev-
`eral times in my travels. The first time, it led to a rather dramatic
`incident. A conscientious student was in charge of showing myslides.
`I started my talk and showed the first slide. When I finished with the
`first slide and asked for the next, the student carefully pushed the
`control button and watched in dismay as the tray backed up, slid out
`of the projector and plopped off the table onto the floor, spilling its
`entire contents. We had to delay the lecture fifteen minutes while I
`struggled to reorganize theslides. It wasn’t the students fault. It was
`the fault of the elegant projector. With only one button to control the
`slide advance, how could one switch from forward to reverse? Neither
`of us could figure out how to make the control work.
`All during the lecture the slides would sometimes go forward, some-
`times backward. Afterward, we found the local technician, who ex-
`plained it to us. A brief push of the button and the slide would go
`
`yw
`
`i
`
`\ick
`Sotclco
`
`Taste (7) fiir Diawechsel am Gerat
`Diawechsel vorwarts = kurz driicken,
`Diawechsel riickwartz = langer driicken.
`
`
`
`Button (7) for changing the slides
`Slide change forward = short press,
`Slide change backward = longerpress.
`
`Slide
`Pravodit
`1.3 Leitz
`I
`finally tracked
`Projector.
`down the instruction manual
`for that projector. A photo-
`graph of the projector hasits
`parts numbered. The button
`for changing slides is number
`7. The buttonitself has no la-
`bels. Who could discover this
`operation without the aid of
`the manual? Hereis the entire
`text related to the button,
`in
`the original Germanand in my
`English translation:
`
`The Psychology of Everyday Things
`
`one: The Psychopathology of Everyday Things
`
`6
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`

`
`
`
`we
`edoT
`vot
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`AS
`
`AF
`Kor
`
`forward, a long push and it would reverse. (Pity the conscientious
`student who kept pushing it hard—and long—to makesure that the
`switch was making contact.) What an elegant design. Why, it managed
`to do two functions with only one button! But Row was a first-time
`user of the projector to know this?
`,
`
`As another example, consider the beautiful Amphithéatre Louis-
`Laird in the Paris Sorbonne, which is filled with magnificentpaintings
`ofgreat figures in French intellectual history. (The mural on the ceiling
`shows lots of naked women floating about a man whois valiantly
`trying to read a book. The painting is right side up only for the lec-
`turer—it is upside down forall the people in the audience.) The room
`is a delightto lecture in, at least until you ask for the projection screen
`to be lowered. “Ah,”says the professor in charge, who gestures to the
`technician, who runs out of the room, up a short flightof stairs, and
`out of sight behind a solid wall. The screen comes down andstops.
`“No, no,” shouts the professor, “a little bit more.” The screen comes
`down again, this time too much. “No, no, no!”the professor jumps up
`and down andgestures wildly. It’s a lovelyroom, with lovelypaintings.
`But why can’t the person whois trying to lower orraise the screen see
`whathe is doing?
`
`New telephone systems have proven to be another excellent exam-
`ple of incomprehensible design. No matter whereI travel, I can count
`upon finding a particularly bad example.
`
`WhenI visited Basic Books, the publishers of this book, I noticed a
`new telephonesystem. I askedpeople howthey liked it. The question
`unleashed a torrent of abuse. “It doesn’t have a hold function,” one
`woman complained bitterly—the same complaintpeople at my univer-
`sity made abouttheir rather different system. In older days, business
`phones always had a button labeled “hold.” You couldpush the button
`and hang up the phone withoutlosing the call on your line. Then you
`could talk to a colleague, orpick up another telephonecall, or even pick
`up the call at anotherphone with the same telephone number. A light
`on the hold button indicated when the function wasin use. It was an
`invaluable tool for business. Why didn’t the newphonesat Basic Books
`or in my university have a hold function,ifit is so essential? Well, they
`did, even the very instrument the woman was complaining about. But
`there was no easy way to discover the fact, nor to learn howto use it.
`I wasvisiting the University ofMichigan and I asked about the new
`
`The Psychology of Everyday Things 1.4 Plate Mounted Over the
`
`Dial of the Telephones at
`the University of Michigan.
`These inadequate instructions
`are all
`that most users see.
`(The button labeled “TAP”at
`the lower
`right
`is used, to
`transfer or pick up calls—it is
`pressed wheneverthe instruc-
`tion plate says “TAP.” The
`light on the lower left comes
`on whenever the telephone
`rings.)
`
`system there. “Yech!” was the response, “and it doesn’t even have a
`hold function!” Here we go again. Whatis going on? The answeris
`simple: first, look at the instructions for hold. At the University of
`Michigan the phone company provided a little plate that fits over the
`keypad and reminds users of the functions and how to use them. I
`carefully unhooked one ofthe plates from the telephone and made a
`Photocopy (figure 1.4). Can you understand how to use it? I can’t.
`There is a “call hold” operation, but it doesn’t make sense to me, not
`for the application that I just described.
`
`Thetelephone holdsituationillustrates a numberof different prob-
`lems. One of them is simply poor instructions, especially a failure to
`relate the new functions to the similarly named functions that people
`already know about. Second, and moreserious,is the lack of visibility of
`the operation of the system. The new telephones,for all their added
`sophistication,lack both the hold button and theflashinglight of the old
`ones. Theholdis signified by an arbitrary action: dialing an arbitrary
`sequence of digits (*8, or *99, or what have you:it varies from one
`phone system to another). Third, there is no visible outcome of the
`operation.
`Devices in the home have developed somerelated problems: func-
`tions and more functions, controls and morecontrols. I do not think
`that simple home appliances—stoves, washing machines, audio and
`television sets—should look like Hollywood's idea of a spaceship con-
`trol room. They already do, muchto the consternation of the consumer
`who, often as not, has lost (or cannot understand) the instruction
`
`one: The Psychopathology of Everyday Things
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`7
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`

`manual, so—faced with the bewildering array of controls and dis-
`plays—simply memorizes one or twofixed settings to approximate
`whatis desired. The whole purpose of the design is lost.
`*
`
`In EnglandI visited a home with a fancy new Italian washer-drier
`combination, with super-duper multi-symbolcontrols, all to do every-
`thing you ever wanted to do with the washing and drying of clothes.
`The husband(an engineering psychologist) said he refused to go near
`it. The wife (a physician) said she had simply memorized onesetting
`andtried to ignore therest.
`Someone wentto a lot of trouble to create that design. I read the
`instruction manual. That machine took into account everything about
`today’s wide variety of synthetic and natural fabrics. The designers
`worked hard; they really cared. But obviously they had never thought
`of trying it out, or of watching anyoneuse it.
`If the design was so bad, if the controls were so unusable, why did
`the couple purchase it? If people keep buying poorly designed pro-
`ducts, manufacturers and designers will think they are doing the right
`thing and continue as usual.
`
`of visibility, appropriate clues, and feedback of one’s actions. These
`principles constitute a form of psychology—the psychology of how
`people interact with things. A British designer once noted that the
`kinds of materials used in the construction of passenger shelters af-
`fected the way vandals responded. He suggested that there might be
`a psychology of materials.
`
`geome Cs)
`
`“In one case, the reinforced glass used to panel shelters (for railroad
`passengers) erected by British Rail was smashed by vandals as fast as
`it was renewed. When the reinforced glass was replaced by plywood
`boarding, however, little further damage occurred, although no extra
`force would have been required to produce it. Thus British Rail
`managed to elevate the desire for defacementto those who could write,
`albeit in somewhat limited terms. Nobody has, as yet, considered
`whether thereis a kind ofpsychology ofmaterials. But on the evidence,
`there could well be!”
`
`
`
`
`
`theinAiliassothepecieandtenreperseFhe
`
`There already exists the start of a psychology of materials and of
`things, the study of affordances of objects. When used in this sense,
`
`The user needs help. Just the right things have to be visible: to
`indicate what parts operate and how,to indicate how the user is to
`interact with the device. Visibility indicates the mapping between in-
`tended actions and actual operations. Visibility indicates crucial dis-
`tinctions—so that youcan tell salt and pepper shakers apart, for exam-
`ple. Andvisibility of the effects of the operationstells you if the lights
`have turned on properly, if the projection screen has lowered to the
`correct height, or if the refrigerator temperature is adjusted correctly.
`It is lack of visibility that makes so many computer-controlled devices
`so difficult to operate. Andit is an excess of visibility that makes the
`gadget-ridden, feature-laden modern audio set or video cassette re-
`corder (VCR) so intimidating.
`
`(see figures 1.5 and 1.6). A chair
`tl
`affords (“is for”) support and, therefore, affordssitting. A chair can also
`be carried. Glass is for seeing through, and for breaking. Wood is
`normally used for solidity, opacity, support, or carving. Flat, porous,
`smooth surfaces are for writing on. So woodis also for writing on.
`Hence the problem for British Rail: when the shelters had glass, van-
`dals smashedit; when they had plywood,vandals wrote on and carved
`it. The planners were trapped by the affordances of their materials.?
`Affordances provide strong clues to the operations of things. Plates
`are for pushing. Knobsare for turning. Slots are for inserting things
`into. Balls are for throwing or bouncing. Whenaffordancesare taken
`advantage of, the user knows what to do just by looking: no picture,
`label, or instruction is required, Complex things may require explana-
`tion, but simple things should not. When simple things needpictures,
`labels, or instructions, the design hasfailed.
`A psychology ofcausality is also at work as we use everydaythings.
`
`The Psychology
`of Everyday Things
`
`This book is about the psychology of everyday things. POET empha-
`sizes the understanding of everyday things, things with knobs and
`dials, controls and switches, lights and meters. The instances we have
`just examined demonstrateseveral principles, including the importance
`
`The Psychology of Everyday Things
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`one: The Psychopathology of Everyday Things
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`pulling.
`
`1.5 Affordances of Doors. Door hardware can signal whether to push or pull
`withoutsigns. Theflat horizontalbar of A (aboveleft) affords no operations except
`pushing:it is excellent hardware for a door that must be pushed to be opened. The
`doorin B (aboveright) has a different kind of bar on eachside, one relatively small
`andvertical to signify a pull, the other relatively large and horizontal to signify a
`push, Both bars support the affordance of grasping: size and position specify
`whetherthe grasp is used to push or pull—though ambiguously.
`
`1.6 WhenAffordances Fail. I hadto tie a string around mycabinet doorto afford
`
`Something that happensright after an action appears to be caused by
`that action. Touch a computer terminal just whenit fails, and you are
`apt to believe that you causedthe failure, even though the failure and
`your action were related only by coincidence. Suchfalse causality is the
`basis for much superstition. Many of the peculiar behaviors of people
`using computer systems or complex household appliances result from
`such false coincidences. When an action has no apparent result, you
`mayconcludethatthe action wasineffective. So yourepeatit. In earlier
`days, when computer word processors did not always showtheresults
`of their operations, people would sometimes attempt to change their
`manuscript, but the lack ofvisible effect from each action would make
`them think that their commands had not been executed, so they would
`repeat the commands, sometimes over andover, to their later astonish-
`mentand regret. It is a poor design that allows either kind of false
`causality to occur.
`
`TWENTY THOUSAND EVERYDAY THINGS
`
`There are an amazing number of everyday things, perhaps twenty
`thousand of them. Are there really that many? Start by looking about
`you. There arelightfixtures, bulbs, and sockets; wall plates and screws;
`clocks, watches, and watchbands. There are writing devices (I count
`twelve in front of me, each different in function, color, or style). There
`are clothes, with different functions, openings, and flaps. Notice the
`variety of materials and pieces. Notice the variety of fasteners—but-
`tons, zippers, snaps, laces. Lookatall the furniture and food utensils:
`all those details, each serving some function for manufacturability,
`usage, or appearance. Consider the workarea: paperclips, scissors, pads
`of paper, magazines, books, bookmarks. In the room I’m workingin,
`I counted more than a hundred specialized objects before I tired. Each
`is simple, but each requires its own method of operation, each has to
`be learned, each does its own specialized task, and each has to be
`designed separately. Furthermore, many of the objects are made of
`manyparts. A desk stapler has sixteen parts, a household ironfifteen,
`the simple bathtub-shower combination twenty-three. You can’t be-
`lieve these simple objects have so manyparts? Hereare the eleven basic
`parts to a sink:drain, flange (around the drain), pop-up stopper, basin,
`soap dish, overflow vent, spout,lift rod,fittings, hot-water handle, and
`cold-water handle. We can count even more if westart taking the
`faucets, fittings, and lift rods apart.
`
`10
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`one: The Psychopathology of Everyday Things
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`
`The book What's What: A Visual Glossary of the Physical World has more
`than fifteen hundred drawings and pictures andillustrates twenty-
`three thousanditemsorparts of items.* Irving Biederman, a psycholo-
`gist who studies visual perception, estimates that there are probably
`“30,000 readily discriminable objects for the adult.’’> Whatever the
`exact number,it is clear that the difficulties of everyday life are ampli-
`fied by the sheer profusion of items. Suppose that each everyday thing
`takes only one minute to learn; learning 20,000 of them occupies
`20,000 minutes—333 hours or about 8 forty-hour work weeks. Fur-
`thermore, we often encounter new objects unexpectedly, when weare
`really concerned with something else. We are confused and distracted,
`and whatoughtto be a simple, effortless, everyday thing interferes
`with the important task of the moment.
`How do people cope? Part of the answerlies in the way the mind
`works—in the psychology of human thought and cognition. Part lies
`in the information available from the appearance of the objects—the
`psychology of everyday things. And part comes from the ability of the
`designer to make the operation clear, to project a good image of the
`operation, and to take advantage of other things people might be ex-
`pected to know. Here is where the designer’s knowledge of the psy-
`chology of people coupled with knowledge of how things work
`becomescrucial.
`
`
`
`1.7 Carelman’s Tandem “Convergent Bicycle (Model for Fiancés).” Jacques
`Carelman: “Convergent Bicycle” Copyright © 1969-76-80 by Jacques Carelman
`and A.D. A. G.P. Paris. From Jacques Carelman,Catalog ofLinfindable Objects, Balland,
`éditeur, Paris-France. Used by permission oftheartist.
`
`the scissors still work. You can figure out the scissors because their
`operating parts are visible and the implications clear. The conceptual
`model is made obvious, and thereis effective use of affordances and
`constraints.
`
`As a counterexample, consider the digital watch, one with two to
`four push buttons on the front or side. What are those push buttons
`for? How would youset the time? There is no wayto tell—no evident
`relationship between the operating controls and the functions, no con-
`straints, no apparent mappings. With the scissors, moving the handle
`makes the blades move. Thewatch and theLeitz slide projector provide
`no visible relationship between the buttons and the possible actions,
`no discernible relationship between the actions and the endresult.
`
`Consider the rather strange bicycle illustrated in figure 1.7. You know
`Principles of Design
`
`it won’t work because you formassontephin!podemotathendevicerands.
`for Understandability and Usability
`
`mentallysimulateitsioperation®You can do the simulation because the
`parts are visible and the implications clear.
`We have now encountered the fundamental principles of designing
`Otherclues to how things work comefrom their visible structure—
`for people: (1) provide a good conceptual model and (2) make things
`visible.
`in particular from affordances, constraints, and mappings. Consider a pair of
`scissors: even if you have never seen or used them before, you can see
`that the numberof possible actions is limited. The holes are clearly
`there to put somethinginto, and the only logical things that will fit are
`fingers. The holes are affordances: they allow the the fingers to be
`inserted. The sizes of the holes provides@a5H#i#B to limit the possible
`fingers: the big hole suggests several fingers, the small hole only one.
`The mapping between holes and fingers—the set of possible opera-
`tions—is suggested and constrained by the holes. Moreover, the opera-
`tion is not sensitive to finger placement: if you use the wrongfingers,
`
`Without a good model weoperate by rote, blindly; we do operations
`as we weretold to do them; wecan’t fully appreciate why, whateffects
`to expect, or what to doif things go wrong. As long as things work
`properly, we can manage. When things go wrong, however, or when
`
`PROVIDE A GOOD CONCEPTUAL MODEL
`
`12
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`The Psychology of Everyday Things
`
`5
`
`eo?
`r ae¥
`U9
`
`one: The Psychopathology of Everyday Things
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`we come upona novelsituation, then we need a deeper understanding,
`a good model.
`For everyday things, conceptual models need not be very complex.
`After all, scissors, pens, and light switches are psetty simple devices.
`There is no need to understand the underlying physics or chemistry of
`each device we own,simply the relationship between the controls and
`the outcomes. When the model presented to us is inadequate or wrong
`(or, worse, nonexistent), we can havedifficulties. Let me tell you about
`myrefrigerator.
`
`My househas an ordinary, two-compartmentrefrigerator—nothing
`very fancy aboutit. The problem is that I can’t set the temperature
`properly. Thereare only two things to do: adjust the temperature ofthe
`freezer compartment and adjust the temperature of the fresh food
`compartment. And there are two controls, one labeled “freezer,” the
`other “fresh food.” What's the problem?
`You try it. Figure 1.8 shows the instruction plate from inside the
`refrigerator. Now, supposethe freezeris too cold, the fresh food section
`just right. You wantto makethe freezer warmer, keeping the fresh food
`constant. Go on, read the instructions, figure them out.
`
`1.8 MyRefrigerator. Two compartments—fresh food and freezer—and two con-
`trols (in the fresh food unit). Theillustration showsthe controls and instructions.
`Your task: Suppose the freezer is too cold, the fresh food section just right. How
`would youadjustthe controls so as to make the freezer warmer and keep the fresh
`food the same? (From Norman, 1986.)
`
`TO STABILIZE
`
`NORMAL SETTINGS
`COLDER FRESH FOOD
`COLDEST FRESH FOOD
`COLDER FREEZER
`WARMERFRESH FOOD
`OFF (FRESH FD & FRZ)
`
`1 SET BOTH CONTROLS
`2 ALLOW 24 HOURS
`
`
`
`
`COOLING UNIT
`
`1.9 Two Conceptual Models for My Refrigerator. The model A (above) is
`provided by the system image oftherefrigerator as gleaned from the controls and
`instructions; B (below)is the correct conceptual model. The problem is thatit is
`impossibleto tell in which compartmentthe thermostatis located and whether the
`
`two controls are in the freezer and fresh food compartment, or vice versa.
`
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`The Psychology of Everyday Things
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`: The Psychopathology of Everyday Things
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`Oh, perhaps I’d better warn you. The two controls are not indepen-
`dent. The freezer control affects the fresh food temperature, and the
`fresh food controlaffects the freezer. And don’t forget to-wait twenty-
`four hours to check on whether you madetherightadjustment, ifyou
`can remember what you did.
`
`Control of the refrigerator is madedifficult because the manufac-
`turer provides a false conceptual model. There are two compartments
`and two controls. The setup clearly and unambiguously provides a
`simple model for the user: each controlis responsible for the tempera-
`ture of the compartmentthatcarries its name. Wrong. In fact, there is
`only one thermostat and only one cooling mechanism. Onecontrol
`adjusts the thermostatsetting, the other the relative proportion of cold
`air sent to each of the two compartmentsofthe refrigerator. This is
`whythe two controls interact. With the conceptual model provided by
`the manufacturer, adjusting the temperatures is almost impossible and
`alwaysfrustrating. Given the correct model, life would be much easier
`(figure 1.9).
`Why did the manufacturer present the wrong conceptual model?
`
`1.10 Conceptual Models. Thedesign modelis the designer’s conceptual model. The
`user's model is the mental model developed through interaction with the system. The
`system image results from the physical structure that has been built (including docu-
`mentation, instructions, and labels). The designer expects the user’s model to be
`identical to the design model. But the designer doesn’t talk directly with the
`user—all communication takes place through the system image. If the system
`image does not make the design model clear and consistent, then theuser will end
`up with the wrong mental model. (From Norman, 1986.)
`
`DESIGN
`
`Perhapsthe designers thought the correct model was too complex, that
`the model they were giving was easier to understand. But with the
`wrong conceptual model,it is impossible to set the controls. And even
`though I am convinced I now know the correct model, I still cannot
`accurately adjust the temperatures because the refrigerator design
`makesit impossible for me to discover which control is for the thermo-
`stat, which control is for the relative proportion of cold air, and in
`which compartment the thermostat is located. The lack of immediate
`feedback for the actions does not help: with a delay of twenty-four
`hours, who can remember what wastried?
`Thetopic of conceptual models will reappear in the book. They are
`part of an important conceptin design:gmemtabi@im@éle; the models people
`have of themselves, others, the environment, and the things with
`which they interact. People form mental models through experience,
`training, and instruction. The mental model of a device is formed
`largely by interpreting its perceived actions andits visible structure. I
`call the visible part of the device the system image (figure 1.10). When
`the system imageis incoherent or inappropriate, as in the case of the
`refrigerator, then the user cannot easily use the device.If it is sen
`plete or contradictory, there will be trouble.
`\e Lawidt
`‘
`on
`(law iS ~T FO -\r
`cot
`ar ws
`\
`\et
`-
`4
`MAKE THINGSVISIBLE >“
`(
`: A bite
`'
`ad
`Theproblems caused by inadequateattention tovisibility are all neatly
`demonstrated with one simple appliance: the modern telephone.
`
`I stand at the blackboard in my office, talking with a student, when
`my telephonerings. Once, twiceit rings. Ipause, trying to complete my
`sentence before answering. The ringing stops. “I’m sorry,” says the
`student. “Not your fault,” I say. “But it’s no problem, the call now
`transfers to my secretary’s phone. She‘ll answerit.” As welisten we r\
`hear her phonestart to ring. Once,
`twice. I look at my watch. Six
`o‘clock: it’s late, the office staff has left for the day. I rush out ofmy See
`office to my secretary’s phone, butas Iget there, it stops ringing. “Ah,”
`I think, “it’s being transferred to another phone.” Sure enough, the
`Phonein the adjacentoffice nowstarts ringing. Irush to that office, but
`it is locked. Back to myoffice to get the key, out to the locked door,
`fumble with thelock, into the office, and to the now quietphone. Ihear
`a telephone downthe hall start to ring. Could thatstill be my call,
`
`a
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`The Psychology of Everyday Things
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`one: The Psychopathology of Everyday Things
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`The modern telephone did not happen bya