One of the reports issuing from the British Association for the Advancement of Science this week announced that computer games can be stress-relieving. For all I know this study may have been subsidised by the Nintendo Institute of Social Sciences but, finding myself at a loose end I went off to Segaworld - a new, multi-level computer theme park in central London - for a few hours of tension-relieving fantasy, blasting jump-suited zombies into puddles of gore and hammering rally cars round virtual race-tracks.

I don't think they sell Valium in the Sega Store, the exit-straddling money-vacuum which is designed to suck the last few coins out of visitors' pockets, but they should think about it. Because the idea that computer games are de-stressing is not exactly borne out by this cacophonous labyrinth, yelping and shrieking with simulated damage and alarm. Nor are the signs warning that it is inadvisable to combine high blood pressure, epilepsy or pregnancy with some of the attractions. You leave Segaworld your blood fizzing with adrenalin and corticotrophin, a ruck of chemical messengers marshalling the organs to battle, calling up sugar reserves, dilating muscular arteries and shutting down vulnerable blood vessels. You are ready to fight giant octopuses in underwater cities or to flee from nameless beasts with glowing eyes. You could probably kill a moose with your bare hands, you're so worked up for fight or flight.

But all you find when you emerge is the dirty grey glare of unaccustomed daylight, an ordinary world where car crashes end in casualty. So you also leave in a peculiarly modern emotional condition - both glutted and unsatisfied, fed up with the jabbing persistence of the sensory assaults, but also twitchily hungry for more.

It isn't even as if the world outside looks tranquil by comparison - because Segaworld alerts you to how universally arousing contemporary life has become. From coffee-shops to advertising hoardings a vast commercial machinery exerts itself to alter our body chemistry - to work on our minds in such a way that our money will follow. And this is, at least in degree, a relative historical novelty. On any given journey in London, for instance, a man will encounter more female erogenous zones than the average Elizabethan probably saw in a year. (Women aren't quite so relentlessly assailed but that's beginning to change. Buy your coffee at the right caffeine-boutique and you could easily find yourself watching a ladder-torsoed young man in wet jeans grinding through a pop song as you wait for your drug to be brewed.)

For men, probably the most conspicuous commercial seduction to be seen at the moment is the bus-stop campaign for Demi Moore's new film Striptease, in which the star sits stark naked, hugging her vestigial modesty to herself in a way that promises its imminent abandonment. Clearly this image is a depleted one - it doesn't have the effect it might do if you turned through your bedroom door and found Demi propped up on your pillows with that inviting smile - but it can't be doing nothing at all. Even if the bell it rings is a distant tinkle down the hall, it presumably has some effect on message systems which have to be employed for some time. Its tepid arousal must, however minutely, adjust your sexual responses, if only by turning down the volume so as to make daily life possible.

Art is not much help in this respect, being quite as efficient at virtual reality as any computer, and just as good at the seductive lie as advertising. Bertolucci's Stealing Beauty, for example, offers male viewers (and maybe some women too) a pretty effective simulation of a summer crush. Cinema has proved itself very good at such feelings, partly because it can fill your field of vision with a face in a way that is only available to lovers in real life. If Liv Tyler's lips were actually that close you would be able to feel her breath on your face. And though this experience is not necessarily superior to that offered by a novel, it is physiologically different. The stimulus isn't reconstructed to your own specifications from verbal code, it is there before you, working directly on that outpost of the brain called the eye. So Bertolucci too is doing his bit to re- engineer the sensorium, that package of messages that makes up our felt experience.

I would guess that it's being re-engineered in the direction of diminished sensitivity. "Try telling your brain it's not real" is the catchphrase attached to much of Segaworld's publicity. It's a motto that will stand just as well for the clamorous, arousing, sleeve-tugging world at large.

Outings, page 13