There they go on their Recorded Tour - a familiar sight in art exhibitions and museums, lost in a world of their own, concentrating. The rest of us might as well not exist. The headphones, and the cumbersome tape machine or CD player hanging by their sides with its strap harnessing their necks, declare what they are about.
Sometimes they are even joined in pairs by wire, as if by umbilical cord, sharing one machine but individual earphones. Major problems can result from such technologically awkward joint ventures when SHE wants to look at the Rothko, while HE is bent on the Hopper.
``Acoustiguide,'' though a trade name, has virtually entered the language (like Hoover or Tupperware) as the word for such guided tours. But the New York-based company is gradually introducing a sophisticated new kind of technology to transform the recorded tour.
A microprocessor-based, digital audio tour system with no headphones, no tapes, no CDs, it is called Inform. The user simply carries a lightweight hand unit just like a slender portable phone.
Inform has some remarkable assets. Its chief one, however, is that it offers ``random access.'' In other words, it makes possible a tour which is not actually guided at all: You can wander at will, like a bee from flower to flower.
Already in operation in the Louvre, Paris; the National Gallery of Art, Washington; the Kunsthaus, Zurich; and nine other institutions worldwide (not all art galleries), Inform has now been introduced at London's Tate Gallery.
The Tate is Britain's premier public collection of modern art, and also of British art of all centuries. Particularly in the modern sections of the museum, visitors are highly selective.
I have seen batches of people march through a gallery scarcely looking right or left. But then they will pore at length over one painting or sculpture, quite fascinated. A recorded tour with a rigid itinerary is not for them.
Inform enables them to walk into a gallery - on Pop and Minimal Art, for instance, or the room entirely devoted to Rothko - and listen at the touch of a few numbers on their handset (the numbers are indicated on the wall) to the voice of a curator explaining some basic concepts about the display.
At least one, and sometimes more of the individual paintings and sculptures in each of the Tate's galleries, now have commentaries programmed into the hand units. Over the next months, the Tate hopes to double the number of these commentaries.
In the Pop and Minimalism gallery - one of the new displays recently set up during the Tate's annual re-hang - you can access Frank Whitford. It is immediately clear from listening that he feels Inform permits a degree of relaxation and informality that a printed wall card would not allow. He suggests you might like to ``walk over and stand on the large square of gray metal tiles.'' Then he adds: ``The object you are now standing on is Carl Andrs `144 Magnesium Square,' and it's a work that typifies both the intellectual and aesthetic concerns of Minimalism.''
If you find you do not like what Mr. Whitford has to say - or would prefer not to stand any longer at his invitation on one of the works - you can press stop and perhaps listen to him talk about Roy Lichtenstein's painting ``Whaam'' of 1963 on the far wall. And you can always rewind him if you want to listen to his pearls of curatorial wisdom over again.
There are further options. Having listened to what a curator says about Henry Moore's bronze ``Falling Warrior,'' you can access a technical discussion on bronze casting by the lost-wax process. Such potential digressions are called ``layers.'' Other layers include recordings of interviews from the Tate archives with artists. You can access Roy Lichtenstein's own voice, for instance. Or David Hockney's.
Less easy to program into the digital memory chips are the voices of - say - 18th-century British artists like Gainsborough or Hogarth. Even advanced late-20th-century technology has not yet cracked the problem of the posthumous voice-over. You can't have everything.
But in the case of Hogarth, curator Andrew Wilton has recorded a particularly intriguing commentary. He talks about two Hogarth paintings. His commentary on ``A Performance of `The Conquest of Mexico' '' struck me as everything it should be. He obviously delights in Hogarth's mix of morality and humor, and relishes the vitality of a painting that in the early 1730s was ``a very advanced picture.''
Mr. Wilton points out one of Hogarth's ``little jokes'' - an empty space on the wall of the room depicted in the painting ``exactly the right size for this very painting, which may have been commissioned to be placed there.'' And another joke, which the artist finally decided against, was a candle dripping wax on the head of a cleric.
Wilton points out that such changes of plan are characteristic of all Hogarth's paintings, and if you look hard you can make out this pentimento. You can see the candle he originally painted under the skin of the paint he brushed over it.
Talking of pentimento - this Inform system makes it easy for changes or additions to be made to the commentaries. The sheer flexibility of this system has remarkable potential for pleasant and instructive communication between museum experts and the lay public. And no wires attached.