Edinburgh Festival: The higher depths: The festival can do strange things to your mind. Thomas Sutcliffe studies the problem

WHAT readers should remember over the next three weeks is that everyone at the Festival will be suffering, to a greater or lesser degree, from the Edinburgh Bends, a mild psychosis induced by living and working under unusual pressures of hype and cultural promise. Like that dangerous condition known to divers as depth narcosis (or Rapture of the Deep), it creeps upon its victim undetected and may indeed be distinctly pleasurable - a sensation of euphoria which is sometimes wrongly attributed to the opportunities afforded by Edinburgh's extended licensing hours.

The real problem is that it is always accompanied by a loss of judgement - rarely fatal in the case of Edinburgh, it's true, but frequently critical. Cramped in the sauna-like conditions of a small fringe theatre, watching a Lithuanian mime- drama about sulphur pollution, writers who have already been exposed to six or seven hours of culture that day can become convinced that they are witnessing a masterpiece. That night, hunched over their lap-tops, they begin to rave.

The truth of this derangement sometimes only emerges months later when, surfing on a wave of Edinburgh praise, the production opens again in a triumphant transfer. Like a hippie finding that he can no longer detect a message of cosmic significance on the cover of his Strawbs album because the LSD has worn off, the critics look in vain for the object of their raptures. Those who booked on the strength of Festival encomiums wonder aloud whether the production has 'lost something in its move away from the smaller space'.

Of course, audiences are not immune to the Edinburgh Bends either, and their susceptibility is further exacerbated by the Pyramid Selling communication system that has evolved to bridge the gap between what's available (around 540 productions on the Fringe this year) and what's managable (six or seven productions a day, if you want to eat). No Edinburgh conversation is complete without an exchange of recommendations; as a result one person will tell five others of their find, they will all tell five more and, before you can say 'Marvellous]' a wildfire hit has emerged from a first night audience of seven.

As the venue won't often hold many more than that, the laws of supply and demand generally drive the play's stock up even further. Like commercial rents, assessments of a production's worth are almost never revised downward in Edinburgh. After all, attendance at a popular production confers a merit which would be devalued by mealy-mouthed recommendations.

Without the Bends Edinburgh can look mystifying - a self-flagellating ordeal of mediocre plays in migraine- forming venues; with them it can be a garden of delights. But to get the Bends you have to go there.