Take the iPod Shuffle. How could you be expected to guess what that tiny metal box does by looking at it? There are no clues to suggest that it might play music. Like most other digital devices, the Shuffle is (literally) an inscrutable box of tricks. Apple’s designers conceived the latest model as a subtle joke on the demise of “form follows ...” It is so small, half the size of its predecessor, that they could make it in the same shape as one of those pins that clip on to clothing. This means the Shuffle’s form does reflect one of its functions, albeit the very minor one of attaching itself to a jacket, but gives no hint as to its more important role of storing and playing hundreds of songs.

Joking aside, the dislocation of form and function has set a new challenge for designers: how to help us to operate ever more complex digital products. In ye olden days when form did follow function, you could guess roughly how to use an object from its appearance. But our ability to work out how to download and play music on a Shuffle is largely determined by the design quality of the software that operates it — the “user interface” in geek-speak, or “U.I.” If the “U.I.” is well designed, you should be able to use the device so intuitively that you will not have to think about it. But if it is badly designed, the process will seem so confusing that you will probably blame yourself for doing something wrong.

Image The iPod Shuffle. Credit... Apple Store

That is why the first wave of U.I. designs sought to reassure us by using visual references to familiar objects to help us to operate digital ones. Take the typewriter keyboards on computers, and video game controllers modeled on TV remote control pads. As our confidence has grown, U.I. design has become more sophisticated, increasingly relating to our physical behavior, rather than objects.

One landmark is Nintendo’s Wii games system, which is operated by replicating the movements we would make if playing for real: from firing a “gun,” to whacking a “tennis ball” with a “racquet.” Another is Apple’s iPhone, which replaced the traditional keyboard with a touch-sensitive screen that achieves a similar effect to the Wii by responding to the natural movements of our hands. The same goes for the thousands of applications, or “apps,” invented for the iPhone, mostly by amateur programmers. Over a billion apps have been downloaded in the last nine months, and one reason for their popularity is that they feel so instinctive. An example is “Brushes,” the $4.99 app with which the artist Jorge Colombo “drew” the cover of the June 1 edition of The New Yorker on his iPhone by creating digital layers of “paint” with his fingers, just as if he was making brushstrokes on a canvas.