Theatres are only now beginning to deal with a crucial issue - the contract between performers and the audience, writes Peter Crawley

About five years ago, through no real fault of his own, Phelim McDermott lost an audience. An actor, director and occasional comedian, he was performing at The Comedy Store in London, where he often appears as part of an improvisation group. Everything was going fantastically well - until one exasperated punter just couldn't take it any more.

"You're just saying things," the heckler said, rising to his feet in frustration, "and people are laughing." McDermott, who told the story at a panel discussion hosted by Theatre Shop recently, on "the role of the audience in the process of theatre production and performance", considered the devastating impact of that simple observation.

"It was kind of like the emperor's new clothes," he told the gathering in Andrews Lane Theatre in Dublin. "Everyone onstage and everyone in the audience realised . . . he was telling the truth. The performers and the audience had agreed to go on a journey together, and that together they would make an experience. When he said this thing it was like it sucked all the atmosphere out of the room and for the next 20 minutes nothing was funny. I think the audience need to know how much influence they have over what they see."

As one of the artistic directors of Improbable, an English company that develops shows largely through improvisation and audience participation, McDermott has always seen the audience as co-creator of an experience, from the instant life-story narrative of Lifegame to the development of the phenomenally successful "junk opera", Shockheaded Peter.

McDermott's examples may be extreme - the role of the spectator as creator writ large - but often the audience, oddly for such an essential part of theatre, tends to be overlooked. Jerzy Grotowski's question, "Can theatre exist without an audience?", which he wrote, with rhetorical flourish, in 1968, would stimulate theatre students for years to come. But his answer - "At least one spectator is needed to make it a performance" - would probably fall short of the projections of any company's marketing department.

If the contract between an audience and performers is a delicate thing ("In lots of ways it's very naive," McDermott says later. "Please tell us a story and we'll enjoy it"), theatres have been developing sophisticated methods to establish audiences, to build them, to categorise them, and to essentially know them.

At the seminar, however, it is difficult to determine whether theatre-makers consider their audience at any time earlier than the first performances. Deborah Shaw, director of the Royal Shakespeare Company's Complete Works festival (which will stage every Shakespeare play, poem and sonnet next year), speaks at length about the festival, but little about its audience; partly, it seems, because with 98 per cent attendance on some shows, the RSC can take audiences for granted.

"Now that's something that can kind of control you as well," Shaw admits. "It's a straitjacket of success, in a way, because it doesn't give you that much room to move. So it's really important that you take risks as well."

Nancy Meckler, co-artistic director of Shared Experience, the English company famed for literary adaptations such as Brontë (which featured in this year's Dublin Theatre Festival), stresses the collaboration that occurs between viewer and performer, but not before the contact of performance.

"I think I would find it difficult to start with [ the question] 'What do I do for this audience?"' says Meckler. "I think it's about making the work you want to make. But you're constantly trying to make work that you think will reach out and connect with people."

One obstacle to involving an audience in the process of theatre production is the difficulty of conceiving an audience before it exists. An audience is an accidental community, one that comes together for a single performance, then disburses immediately after it.

By definition, they're hard to plan for: myriad different factors can conspire to make for a "wonderful audience" or a "tough crowd".

The film industry may have a more rigorous method, where a complicated system of test audiences, surveys and focus groups is often employed in order to ruin a good film, but theatre makers have learned from their audiences through response.

Vsevolod Meyerhold, the Soviet director, even developed a neat system of notation to record an audience's reactions. It began: (a) silence; (b) noise; (c) loud noise, skipped through (f) coughing or (j) weeping; before culminating in (p) hisses; (q) people leaving; (r) people getting out of their seats; (s) throwing of objects; (t) people getting onto stage. By any standards, a category (t) must have been a pretty eventful night.

At Theatre Shop's seminar, McDermott has something to say about (q). "I think people leaving is really interesting," he said, as guilty parties trickle out of the seminar early. "If only, in the West End, when people were really bored, they really left. And they didn't just sit there thinking, 'Is this any good? I read the review and it said it was good.' If the audience trusted itself more to leave when they were bored, theatre would get better." As for getting them there in the first place, the panel chairman, Gerard Stembridge, asks Deborah Shaw if the RSC knows of any "black arts". "Well, that's called marketing," comes her reply.

In the office of Project Arts Centre in Dublin a few days after the seminar, communications officer Dairne O'Sullivan runs a computer programme, common to most theatres, called Databox. Each time the theatre sells a ticket, the customer information is stored in the system; if you've ever used a credit card in Project, Databox knows about you.

O'Sullivan demonstrates how a dance company might quickly find out who Project's dance fans were and where they lived. She clicks on a few dance titles, and Databox scans the 18,555 people in its records. Within a few seconds, a list of 52 names and addresses is primed and ready for a special-offer mail-out. Audiences, however, remain notoriously unpredictable.

"My feeling is that Irish audiences don't like to commit," says O'Sullivan. "We can tell from this that most of our bookings are done the day before." And as for the hypothetical mail-out, O'Sullivan is unconvinced by its effectiveness. "Word of mouth is still the most effective way of marketing something."

Yet audience development and the burgeoning role of the audience development officer continue apace: Draíocht Arts Centre in Blanchardstown, Dublin, has even started communicating with its audience by text message, while the Abbey recently underwent a pilot research project with something called a socio-geodemographic profiling system.

It established, to nobody's particular surprise, that the theatre's audience was older, affluent, urban and socially mobile. The report's conclusions (one wondered whether the Abbey could "broaden out into other types of entertainment") seemed less helpful. Go-karting, perhaps?

Few theatres in Dublin seem to be able to depend on a core audience, but one theatre's audience is apparently so identifiable it can be recognised adrift in the foyers of other theatres.

"I remember at the first B*Spoke production, Electra, in Project, I was walking up the stairs behind these people who were obviously a Gate audience," says O'Sullivan. "They said, 'Is the seating numbered?' And this guy turns around and says, 'No, it's like Ryanair here'."

For his part, Michael Colgan, artistic director of Dublin's Gate Theatre, admits that the theatre attracts a very high figure - it averages between 82 and 84 per cent attendance - and explains the loyalty of its audience is as much a result of the aesthetics of the building - "It feels like going into somebody's home," says Colgan - as the 22 years of his artistic policy.

But there can be a drawback to the loyalty engendered by a Georgian theatre with four chandeliers. Drawing room comedies may settle snugly into the theatre's decorous architecture, but in 2003 audiences didn't know what to make of Mark O'Rowe's grimy and harrowing contemporary drama, Crestfall.

"He's probably one of the greatest young talents around," Colgan says of O'Rowe. "We did a production that I was very proud of. It was a hugely happy experience, and in terms of box office it was one of the biggest disasters we've ever had. I often wonder, had I produced it at The Project, would that have been seen as a success and would I have done a greater service to Mark O'Rowe?"

Either way, Colgan is currently talking to O'Rowe about staging another play. "If Crestfall was a shock to the system, then I think we need more shocks to the system. Don't forget that the system changes. People change. Audiences change."

Back at the seminar, I ask Phelim McDermott about one unchanging aspect of the apparently unpredictable, unknowable audience: its applause.

The curtain call is something more than just positive feedback, it's a confirmation that a performance has made sense, that in the theatre we all have a part to play.

"A weird thing happens in a curtain call," McDermott agrees. "One version is that when actors go onstage they show things that are larger than life; they're epic, they're mythic. But in the process of doing a curtain call, they bow to the audience. That's why curtain calls are really important.

"There's an honouring of the audience in that process: 'This wouldn't have happened if it weren't for you. Thank you very much'." What kind of crowd are we, then? McDermott unleashes his inner luvvie. "I thought you were marvellous, darling!"