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A Theory of My Own: Explaining the strange sensation of getting nowhere very fast: Brian Simpson continues our occasional series by examining the 'Escalator Effect'

LONDONERS do not realise how fortunate they are to have, in their underground railway system, one of the world's finest collections of stationary escalators. I first realised the value of these non-functional machines when I set foot upon the escalator at Archway station - surely one of the finest and most renowned examples of the stationary genre - and noticed, just for a split second, that it appeared to be going backwards.

I was immediately aware of being in the presence of an illusion of great significance. The 'Escalator Effect', as I called it, would not expedite my journey but I knew that it had the power to illuminate the human psyche.

The sensation of movement contradicted all evidence: I could clearly see that nothing was moving. Yet I definitely felt it. And I felt it again at the far end of the escalator as I got off. Eager to discover what other psychologists thought of this illusion, I trawled the academic literature for references to escalators. I was astonished to find only one article: a short piece purporting to explain why people felt dizzy and fell over on moving escalators. On the subject of stationary escalators, there was nothing.

The only well-researched illusion that is even remotely comparable to the 'Escalator Effect' is the 'Duncker Effect', which occurs in stationary trains. Another train goes past on the adjacent track and you think, mistakenly, that your own train is moving. It demonstrates the inherent relativity of movement perception: something is moving, but you are confused about precisely what. The 'Escalator Effect' is different, for here nothing is moving but something feels as though it is.

So how can it be explained? I believe we become so accustomed to the potentially unbalancing experience of being whisked forwards by moving escalators that our brains automatically compensate for the expected sensation, effectively cancelling it out with a kind of conditioned mental reflex. When an escalator is stationary the compensatory reflex is inappropriate and produces a sensation of reversed movement. I am told the effect is even more pronounced on broken-down travelators.

Such illusions are more than mere perceptual curiosities. Recently a Lufthansa A320 Airbus failed to stop in time after landing at Warsaw airport. It crashed into an embankment and burst into flames. Marcin Bronikowski, a survivor, was reported as saying that 'after the landing . . . instead of the plane losing speed, it started to gain speed on the runway'. This apparent acceleration could easily have been an illusion related to the 'Escalator Effect'.

Owing to a mechanical defect, the plane's reverse-thrust and braking systems had not been activated until 700 metres after touchdown. If, as is likely, the plane did decelerate on landing, but not as rapidly as usual, then relative to Mr Bronikowski's expectations it could have seemed to be picking up speed.

I once had a similar experience when my car's brakes partially failed. For a moment it felt as though pressing the brake pedal was causing the car to accelerate.

Neither are 'Escalator Effects' confined to illusions of movement. They can occur whenever reality fails to live up to expectations. Politicians, business leaders and advertisers often create such effects by raising expectations too high, thus guaranteeing disappointment - economic, social or in the whiteness of one's washing. This is not merely a question of being 'saddened by the failure of an expectation', as the dictionary defines 'disappointment'. By virtue of 'Escalator Effects', over-optimistic expectations have to power to diminish our perceptions.

But if the 'Escalator Effect' is caused by failed expectations, what will happen if, as a result of reading this piece, you expect an 'Escalator Effect'? Will the expectation kill it? In the short term it won't, but massive exposure to stationary escalators, as experienced on the Northern Line, could probably extinguish or even reverse the effect.

The management of London Underground say they are 'flattered to be contributing to academic research' by providing the tools for the stationary-escalator researcher. They have given me their assurance that although the current embarrassment of riches may not continue for ever, 'the dedicated psychologist should always be able to find one or two machines stationary'.

(Photograph omitted)