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down, turning the task over to people, often without warning. Well, with naturalistic, continual feedback, there will be warning.
Implicit Signals and Communication
    Whenever I walk into a research laboratory, I look to see how neat or messy it is. When everything is orderly, everything in itsplace, I suspect this is a laboratory where not much work is being done. I like to see disorder: that means active, engaged people. Disorder is a natural, implicit sign of activity.
    We leave traces of our activities: footprints in the sand, litter in the trash, books on desks, counters, and even the floor. In the academic field of semiotics, these are called signs or signals. To the reader of detective novels, they are called clues, and ever since the perceptive eye of Sherlock Holmes entered the world of detectives, they have provided the evidence of people’s activities. These nonpurposeful clues are what the Italian cognitive scientist Cristiano Castlefranchi calls “implicit communication.” Castlefranchi defines behaviorally implicit communication as natural side effects that can be interpreted by others. It “does not require a specific learning or training, or transmission,” says Castlefranchi. “It simply exploits perceptual patterns of usual behavior and their recognition.” Implicit communication is an important component of the design of intelligent things because it informs without interruption, annoyance, or even the need for conscious attention.
    Footprints, disorderly research laboratories, underlining and sticky notes on reading matter, the sounds of elevators or of a home’s appliances: all are natural, implicit signals that allow us to infer what is happening, to remain aware of the activities in the environment, to know when it is time to step in and take action and when it is possible to ignore them and continue with whatever we are doing.
    A good example comes from the world of the old-fashioned telephone. In the old days, when making an international phone call, clicks and hisses and noises let you know thatprogress was being made, and through the differing sounds, you could even learn how well things were progressing. As equipment and technology got better, the circuits became quieter, until they became noise free. Oops, all the implicit clues were gone. People waiting on the line heard silence, which they sometimes interpreted to mean the call had failed, so they hung up. It was necessary to reintroduce sounds into the circuit so people would know that the call was still being processed. “Comfort noise” is what the engineers called it, their condescending way of responding to the needs of their customers. The sounds are far more than “comfort.” They are implicit communication, confirming that the circuit is still active, informing the telephone caller that the system is still in the process of making the connection. And, yes, that implicit confirmation is reassuring, comforting.
    Although sound is important for providing informative feedback, there is a downside. Sounds are often annoying. We have eyelids that permit us to shut out scenes we do not wish to watch: there are no earlids. Psychologists have even devised scales of annoyance for rating noise and other sounds. Unwanted sound can disrupt conversations, make it difficult to concentrate, and disturb tranquil moments. As a result, much effort has gone into the development of quieter devices in the office, factory, and home. The automobile has become so quiet that many years ago Rolls-Royce used to brag that “at 60 mph the loudest noise in this new Rolls-Royce comes from the electric clock.”
    Although quiet can be good, it can also be dangerous. Without noise from the environment, the automobile driver can’t beaware of the sirens of emergency vehicles, or the honking of horns, or even the weather. If all roads feel equally smooth, regardless of their actual condition, regardless of how fast