by Don Norman
PEOPLE’S RESPONSES TO CHANGES IN CONVENTIONS
People invariably object and complain whenever a new approach is introduced into an existing array of products and systems. Conventions are violated: new learning is required. The merits of the new system are irrelevant: it is the change that is upsetting. The destination control elevator is only one of many such examples. The metric system provides a powerful example of the difficulties in changing people’s conventions.
The metric scale of measurement is superior to the English scale of units in almost every dimension: it is logical, easy to learn, and easy to use in computations. Today, over two centuries have passed since the metric system was developed by the French in the 1790s, yet three countries still resist its use: the United States, Liberia, and Myanmar. Even Great Britain has mostly switched, so the only major country left that uses the older English system of units is the United States. Why haven’t we switched? The change is too upsetting for the people who have to learn the new system, and the initial cost of purchasing new tools and measuring devices seems excessive. The learning difficulties are nowhere as complex as purported, and the cost would be relatively small because the metric system is already in wide use, even in the United States.
Consistency in design is virtuous. It means that lessons learned with one system transfer readily to others. On the whole, consistency is to be followed. If a new way of doing things is only slightly better than the old, it is better to be consistent. But if there is to be a change, everybody has to change. Mixed systems are confusing to everyone. When a new way of doing things is vastly superior to another, then the merits of change outweigh the difficulty of change. Just because something is different does not mean it is bad. If we only kept to the old, we could never improve.
The Faucet: A Case History of Design
It may be hard to believe that an everyday water faucet could need an instruction manual. I saw one, this time at the meeting of the British Psychological Society in Sheffield, England. The participants were lodged in dormitories. Upon checking into Ranmoor House, each guest was given a pamphlet that provided useful information: where the churches were, the times of meals, the location of the post office, and how to work the taps (faucets). “The taps on the washhand basin are operated by pushing down gently.”
When it was my turn to speak at the conference, I asked the audience about those taps. How many had trouble using them? Polite, restrained tittering from the audience. How many tried to turn the handle? A large show of hands. How many had to seek help? A few honest folks raised their hands. Afterward, one woman came up to me and said that she had given up and walked the halls until she found someone who could explain the taps to her. A simple sink, a simple-looking faucet. But it looks as if it should be turned, not pushed. If you want the faucet to be pushed, make it look as if it should be pushed. (This, of course, is similar to the problem I had emptying the water from the sink in my hotel, described in Chapter 1.)
Why is such a simple, standard item as a water faucet so difficult to get right? The person using a faucet cares about two things: water temperature and rate of flow. But water enters the faucet through two pipes, hot and cold. There is a conflict between the human need for temperature and flow and the physical structure of hot and cold.
There are several ways to deal with this:
•Control both hot and cold water: Two controls, one for hot water, the other cold.
•Control only temperature: One control, where rate of flow is fixed. Rotating the control from its fixed position turns on the water at some predetermined rate of flow, with the temperature controlled by the knob position.
•Control only amount: One control, where temperature is fixed, with rate of flow controlled by the knob position.
•On-off. One control turns the water on and off. This is how gesture-controlled faucets work: moving the hand under or away from the spout turns the water on or off, at a fixed temperature and rate of flow.
•Control temperature and rate of flow. Use two separate controls, one for water temperature, the other for flow rate. (I have never encountered this solution.)
•One control for temperature and rate: Have one integrated control, where movement in one direction controls the temperature and movement in a different direction controls the amount.
Where there are two controls, one for hot water and one for cold, there are four mapping problems;
•Which knob controls the hot, which the cold?
•How do you change the temperature without affecting the rate of flow?
•How do you change the flow without affecting the temperature?
•Which direction increases water flow?
The mapping problems are solved through cultural conventions, or constraints. It is a worldwide convention that the left faucet should be hot; the right, cold. It is also a universal convention that screw threads are made to tighten with clockwise turning, loosen with counterclockwise. You turn off a faucet by tightening a screw thread (tightening a washer against its seat), thereby shutting off the flow of water. So clockwise turning shuts off the water, counterclockwise turns it on.
Unfortunately, the constraints do not always hold. Most of the English people I asked were not aware that left/hot, right/cold was a convention; it is violated too often to be considered a convention in England. But the convention isn’t universal in the United States, either. I once experienced shower controls that were placed vertically: Which one controlled the hot water, the top faucet or the bottom?
If the two faucet handles are round knobs, clockwise rotation of either should decrease volume. However, if each faucet has a single “blade” as its handle, then people don’t think they are rotating the handles: they think that they are pushing or pulling. To maintain consistency, pulling either faucet should increase volume, even though this means rotating the left faucet counterclockwise and the right one clockwise. Although rotation direction is inconsistent, pulling and pushing is consistent, which is how people conceptualize their actions.
Alas, sometimes clever people are too clever for our good. Some well-meaning plumbing designers have decided that consistency should be ignored in favor of their own, private brand of psychology. The human body has mirror-image symmetry, say these pseudo-psychologists. So if the left hand moves clockwise, why, the right hand should move counterclockwise. Watch out, your plumber or architect may install a bathroom fixture whose clockwise rotation has a different result with the hot water than with the cold.
As you try to control the water temperature, soap running down over your eyes, groping to change the water control with one hand, soap or shampoo clutched in the other, you are guaranteed to get it wrong. If the water is too cold, the groping hand is just as likely to make the water colder as to make it scalding hot.
Whoever invented that mirror-image nonsense should be forced to take a shower. Yes, there is some logic to it. To be a bit fair to the inventor of the scheme, it works as long as you always use two hands to adjust both faucets simultaneously. It fails miserably, however, when one hand is used to alternate between the two controls. Then you cannot remember which direction does what. Once again, notice that this can be corrected without replacing the individual faucets: just replace the handles with blades. It is psychological perceptions that matter—the conceptual model—not physical consistency.
The operation of faucets needs to be standardized so that the psychological conceptual model of operation is the same for all types of faucets. With the traditional dual faucet controls for hot and cold water, the standards should state:
•When the handles are round, both should rotate in the same direction to change water volume.
•When the handles are single blades, both should be pulled to change water volume (which means rotating in opposite directions in the faucet itself).
Other configurations of handles are possible. Suppose the handles are mounted on a horizontal axis so that they rotate vertically. Then what? Would the answer di
ffer for single blade handles and round ones? I leave this as an exercise for the reader.
What about the evaluation problem? Feedback in the use of most faucets is rapid and direct, so turning them the wrong way is easy to discover and correct. The evaluate-action cycle is easy to traverse. As a result, the discrepancy from normal rules is often not noticed—unless you are in the shower and the feedback occurs when you scald or freeze yourself. When the faucets are far removed from the spout, as is the case where the faucets are located in the center of the bathtub but the spouts high on an end wall, the delay between turning the faucets and the change in temperature can be quite long: I once timed a shower control to take 5 seconds. This makes setting the temperature rather difficult. Turn the faucet the wrong way and then dance around inside the shower while the water is scalding hot or freezing cold, madly turning the faucet in what you hope is the correct direction, hoping the temperature will stabilize quickly. Here the problem comes from the properties of fluid flow—it takes time for water to travel the 2 meters or so of pipe that might connect the faucets with the spout—so it is not easily remedied. But the problem is exacerbated by poor design of the controls.
Now let’s turn to the modern single-spout, single-control faucet. Technology to the rescue. Move the control one way, it adjusts temperature. Move it another, it adjusts volume. Hurrah! We control exactly the variables of interest, and the mixing spout solves the evaluation problem.
Yes, these new faucets are beautiful. Sleek, elegant, prize winning. Unusable. They solved one set of problems only to create yet another. The mapping problems now predominate. The difficulty lies in a lack of standardization of the dimensions of control, and then, which direction of movement means what? Sometimes there is a knob that can be pushed or pulled, rotated clockwise or counterclockwise. But does the push or pull control volume or temperature? Is a pull more volume or less, hotter temperature or cooler? Sometimes there is a lever that moves side to side or forward and backward. Once again, which movement is volume, which temperature? And even then, which way is more (or hotter), which is less (or cooler)? The perceptually simple one-control faucet still has four mapping problems:
•What dimension of control affects the temperature?
•Which direction along that dimension means hotter?
•What dimension of control affects the rate of flow?
•Which direction along that dimension means more?
In the name of elegance, the moving parts sometimes meld invisibly into the faucet structure, making it nearly impossible even to find the controls, let alone figure out which way they move or what they control. And then, different faucet designs use different solutions. One-control faucets ought to be superior because they control the psychological variables of interest. But because of the lack of standardization and awkward design (to call it “awkward” is being kind), they frustrate many people so much that they tend to be disliked more than they are admired.
Bath and kitchen faucet design ought to be simple, but can violate many design principles, including:
•Visible affordances and signifiers
•Discoverability
•Immediacy of feedback
Finally, many violate the principle of desperation:
•If all else fails, standardize.
Standardization is indeed the fundamental principle of desperation: when no other solution appears possible, simply design everything the same way, so people only have to learn once. If all makers of faucets could agree on a standard set of motions to control amount and temperature (how about up and down to control amount—up meaning increase—and left and right to control temperature, left meaning hot?), then we could all learn the standards once, and forever afterward use the knowledge for every new faucet we encountered.
If you can’t put the knowledge on the device (that is, knowledge in the world), then develop a cultural constraint: standardize what has to be kept in the head. And remember the lesson from faucet rotation on page 153: The standards should reflect the psychological conceptual models, not the physical mechanics.
Standards simplify life for everyone. At the same time, they tend to hinder future development. And, as discussed in Chapter 6, there are often difficult political struggles in finding common agreement. Nonetheless, when all else fails, standards are the way to proceed.
Using Sound as Signifiers
Sometimes everything that is needed cannot be made visible. Enter sound: sound can provide information available in no other way. Sound can tell us that things are working properly or that they need maintenance or repair. It can even save us from accidents. Consider the information provided by:
•The click when the bolt on a door slides home
•The tinny sound when a door doesn’t shut right
•The roaring sound when a car muffler gets a hole
•The rattle when things aren’t secured
•The whistle of a teakettle when the water boils
•The click when the toast pops up
•The increase in pitch when a vacuum cleaner gets clogged
•The indescribable change in sound when a complex piece of machinery starts to have problems
Many devices simply beep and burp. These are not naturalistic sounds; they do not convey hidden information. When used properly, a beep can assure you that you’ve pressed a button, but the sound is as annoying as informative. Sounds should be generated so as to give knowledge about the source. They should convey something about the actions that are taking place, actions that matter to the user but that would otherwise not be visible. The buzzes, clicks, and hums that you hear while a telephone call is being completed are one good example: take out those noises and you are less certain that the connection is being made.
Real, natural sound is as essential as visual information because sound tells us about things we can’t see, and it does so while our eyes are occupied elsewhere. Natural sounds reflect the complex interaction of natural objects: the way one part moves against another; the material of which the parts are made—hollow or solid, metal or wood, soft or hard, rough or smooth. Sounds are generated when materials interact, and the sound tells us whether they are hitting, sliding, breaking, tearing, crumbling, or bouncing. Experienced mechanics can diagnosis the condition of machinery just by listening. When sounds are generated artificially, if intelligently created using a rich auditory spectrum, with care to provide the subtle cues that are informative without being annoying, they can be as useful as sounds in the real world.
Sound is tricky. It can annoy and distract as easily as it can aid. Sounds that at one’s first encounter are pleasant or cute easily become annoying rather than useful. One of the virtues of sounds is that they can be detected even when attention is applied elsewhere. But this virtue is also a deficit, for sounds are often intrusive. Sounds are difficult to keep private unless the intensity is low or earphones are used. This means both that neighbors may be annoyed and that others can monitor your activities. The use of sound to convey knowledge is a powerful and important idea, but still in its infancy.
Just as the presence of sound can serve a useful role in providing feedback about events, the absence of sound can lead to the same kinds of difficulties we have already encountered from a lack of feedback. The absence of sound can mean an absence of knowledge, and if feedback from an action is expected to come from sound, silence can lead to problems.
WHEN SILENCE KILLS
It was a pleasant June day in Munich, Germany. I was picked up at my hotel and driven to the country with farmland on either side of the narrow, two-lane road. Occasional walkers strode by, and every so often a bicyclist passed. We parked the car on the shoulder of the road and joined a group of people looking up and down the road. “Okay, get ready,” I was told. “Close your eyes and listen.” I did so and about a minute later I heard a high-pitched whine, accompanied by a low humming sound: an automobile was approaching. As it came closer, I could hear tire noise. After the car had passed,
I was asked my judgment of the sound. We repeated the exercise numerous times, and each time the sound was different. What was going on? We were evaluating sound designs for BMW’s new electric vehicles.
Electric cars are extremely quiet. The only sounds they make come from the tires, the air, and occasionally, from the high-pitched whine of the electronics. Car lovers really like the silence. Pedestrians have mixed feelings, but the blind are greatly concerned. After all, the blind cross streets in traffic by relying upon the sounds of vehicles. That’s how they know when it is safe to cross. And what is true for the blind might also be true for anyone stepping onto the street while distracted. If the vehicles don’t make any sounds, they can kill. The United States National Highway Traffic Safety Administration determined that pedestrians are considerably more likely to be hit by hybrid or electric vehicles than by those that have an internal combustion engine. The greatest danger is when the hybrid or electric vehicles are moving slowly, when they are almost completely silent. The sounds of an automobile are important signifiers of its presence.
Adding sound to a vehicle to warn pedestrians is not a new idea. For many years, commercial trucks and construction equipment have had to make beeping sounds when backing up. Horns are required by law, presumably so that drivers can use them to alert pedestrians and other drivers when the need arises, although they are often used as a way of venting anger and rage instead. But adding a continuous sound to a normal vehicle because it would otherwise be too quiet, is a challenge.
What sound would you want? One group of blind people suggested putting some rocks into the hubcaps. I thought this was brilliant. The rocks would provide a natural set of cues, rich in meaning yet easy to interpret. The car would be quiet until the wheels started to turn. Then, the rocks would make natural, continuous scraping sounds at low speeds, change to the pitter-patter of falling stones at higher speeds, the frequency of the drops increasing with the speed of the car until the car was moving fast enough that the rocks would be frozen against the circumference of the rim, silent. Which is fine: the sounds are not needed for fast-moving vehicles because then the tire noise is audible. The lack of sound when the vehicle was not moving would be a problem, however.
