Simpson, B. (1992) The escalator effect. The Psychologist, 5, No 10 (October) 462-3.    
Sheet 11 (bottom)
The phenomenon

“Upon setting foot on the first tread of a stationary escalator, the traveller experiences a strange sensation of movement.”

The explanation

“From a physiological point of view, it seems that we become so well prepared to receive certain messages from our vestibular (inner-ear balance) mechanism and from muscular proprioceptors that such messages, when they arrive, are effectively discounted. Only if the escalator is stationary are we suddenly made aware of it - as a strip of floor that is moving backwards relative to our expectations.

Such mental preparation is apparently unconscious, and it would appear to take the form of a reflex that becomes strongly conditioned to the whole range of visual stimuli associated with escalators (i.e. to the appearance of escalators and not just to the movement of their treads and handrails).

The escalator effect is not at all easy to disrupt, diminish or destroy, however much one concentrates on the fact that the stationary escalator is just like any normal staircase. Perhaps it is only for some Northern Line passengers, with their unparalleled experience of stationary escalators, that the effect is ever extinguished.”

Comment

The effect is  independent of rational cognitive analysis. (I.e. it is involuntary. This could be related to the fact that not all vestibular [inner-ear balance] information reaches the cortex.)