s American Airlines Flight 965 prepared to make a night approach into the deep valley that holds the Cali, Colombia, airport, the pilots made a tiny mistake.
They wanted to direct the plane toward a navigation beacon known as ''R-Rozo,'' but instead selected from their computer's menu the name of a nearby beacon with an almost identical designation, ''R-Romeo.'' The error sent the Boeing 757 slamming into the peak of a nearby mountain, killing 159 people.
As the nation debated whether a confusing menu of ballot options in Florida foiled the people's will, scientists said the 2000 election, like the 1995 plane crash, raises one of the most profound and underappreciated technological challenges of the new century: How to build machines that are easy to use?
With the headlong rush into the future, these scientists say, mankind has been beaten down by the things it built, by voice mail systems that don't answer questions, by VCRs that don't listen, by interfaces so confusing that a few errant key strokes can put a nuclear reactor on critical, send an overdose surging into a patient, or elect the wrong man president of the United States.
''One hundred and fifty years after the abolition of slavery, we have surrendered ourselves and become slaves to these machines,'' said Michael L. Dertouzos, director of MIT's Laboratory for Computer Science. ''We've been kneeling down and speaking to the machines at their level. Now, it's time to focus on the intersection of what computers can do and what we want.''
At the vanguard are laboratories at the Massachusetts Institute of Technology, and around the country, which are working to completely re-imagine the way man and machine communicate. Instead of relying on awkward keyboards and levers, they are building devices that understand spoken directions, follow hand gestures, infer emotional states, and give feedback using touch and even smell.
A California-based company called DigiScents, for example, plans to offer a mechanism next year that will give computers the ability to deliver scent signals, and even download digital ''scent streams'' from Web sites, by combining 128 perfumes in the same way a monitor creates colors by combining red, green, and blue.
''What we're doing is a fairly qualitative leap that will allow people to feel much more immersed in what they are doing,'' said DigiScents cofounder Joel Lloyd Bellenson. In the future, then, e-shoppers will be able to sniff a candle, a dessert, or a bouquet of flowers before they buy.
As Web sites claim an ever larger part of the visual landscape, and as an aging population finds itself increasingly overwhelmed by the new environment, a cottage industry of interface gurus has grown up to meet the demand. The annual conference of the Usability Professionals' Association had 495 attendees in 1999, and more than 700 this year.
''The second [companies] make a Web site easier to use, sales explode,'' said Jakob Nielsen, a well-known critic of Web-page design who charges a $35,000 consulting fee to make sites more intuitive.
Nielsen and his colleagues say that Palm Beach County's butterfly ballot is a classic case of designers' making a task easy for the machine, not the person. The voters were given a row of holes to punch down the center, with the names of the candidates stacked on either side.
Because it was easy to confuse the holes for Gore and Buchanan, the ballot defies what engineers call the ''principle of graceful degradation'': A mistake that would be easy for a human to make, such as confusing ''R-Rozo'' and ''R-Romeo,'' should not have catastrophic consequences.
This is why, for example, computers now ask if you really want to delete those files, or why it would be a bad idea to locate a button that sends a nuclear missile flaming from its silo next to the power switch for the coffee maker.
Donald Norman, author of ''The Design of Everyday Things,'' said people spend their days surrounded by an irritating design flaw he calls ''bad mapping.'' The butterfly ballot, for example, is confusing in the same way the straight line of controls on the front of most stoves makes it easy to turn off the wrong burner.
The hallmark of a good design, he said, is that it makes people look smart, not stupid. ''Yet when something goes wrong, we like to blame the people, to scold or fire them,'' said Norman.
Good machine interfaces are often so intuitive that we find it hard to imagine what came before: Youngsters undoubtedly look at the rotary phone with the same surprise and confusion their parents feel seeing the tiller that was used to control cars before the steering wheel was implemented.
The mouse and desktop system championed by Apple Computer Inc. and known as a ''graphical user interface'' is a drastic improvement over its precursors, designers said, because it allows the user to process information in a more human way. Even children understand pointing and clicking, but most adults would rather avoid the strings of letters, colons, dots, and slashes that computers process with glee.
Still, computers are a long way from being truly usable, according to Dertouzos, who recently wrote that calling today's computers ''user friendly'' would be ''tantamount to dressing a chimpanzee in a green hospital gown and earnestly parading it as a surgeon.''
Dertouzos is the author of a new book, scheduled for January publication, called ''The Unfinished Revolution: Human Centered Computers and What They Can Do for Us.''
Ted Selker, a professor at MIT's Media Lab, said that the ultimate challenge is to make a tool so elegant that people forget they are even using it.
''A good interface takes the tool out of the task,'' said Selker, who directs a laboratory on context-aware computing, machines that infer what people are trying to do so they can help them. His prototypes include the ''Intelligent Bed,'' the ''Talking Trivet,'' and a digitally enhanced door that knows who is in a room and has an electronic meeting scheduler embedded in it.
But as engineers make the links between people and devices more seamless, there are also new dangers. Auto companies are working on an enhanced version of cruise control that would apply the brakes if it detected a car ahead, but now they worry people will come to rely on the control too heavily and pay less attention to driving, according to MIT professor Thomas Sheridan.
''Sometimes to get people to pay attention, you have to design the system to be less than ideal,'' said Selker, who explained that when he kayaks, he is more likely to flip after the most difficult section, when he lets his guard down.
Whenever a task becomes too easy - be it driving a car or electing public officials in our democracy - people will become careless, and, sooner or later, the accumulation of small errors will crash the system.
