Sensory Integration Minute – Broken Escalator

Broken Escalator

Some of you listening tonight may have experienced the ’broken escalator phenomenon’, namely the sensation that when walking onto an escalator that is stationary, you experienced an odd sensation of imbalance, despite the knowledge that the escalator wasn’t going to move. This is a particularly interesting phenomenon because it represents a rare example of the dissociation between knowledge of the world and subsequent action. A couple of professors at the Imperial College of London, Drs. Reynolds and Bronstein, have investigated this phenomenon. They first had people walk down a short walkway, step on a stationary platform that was embedded into the floor and then keep walking. During the experiments they measured walking velocity. Next they had people practice walking onto the same platform only this time the platform was moving. The platform moved forward just like an escalator does. During their initial experiments, they had the subjects practice walking onto the moving platform 20 times and then told them that during the next set of trials the platform would no longer be moving. Consistent with the broken elevator phenomenon, the subjects approached the platform at a higher walking velocity than when they had previously practiced without the platform moving. This resulted in a large overshoot of their trunk such that they swayed forward with many subjects being forced to reach out and grab a handrail to keep from falling. Aftereffects such as this one are occasionally seen in movement-related experiments after subjects practice a large number of trials in a certain condition and then move to a new condition.

What is interesting about this particular phenomenon is that the professors redid the experiment but this time they provided the subjects only one practice trial in which the platform was moving. Nonetheless, when they told the subjects that during the next trial the platform would not be moving, the subjects still displayed the inappropriate behavior, again resulting in a large overshoot and loss of balance. This broken escalator phenomenon is an interesting example of how accurate sensory information and knowledge can be ignored by the central nervous system and lead to dangerous situations.

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