Asked by: Geethu Thomas, Surrey


Scientists have approached this difficult question by timing how long it takes us to become consciously aware of sensory information. By some estimates, we can experience sensory stimuli that’s presented for as little as 50 milliseconds (about one-twentieth of a second). It is thought that our brains can, in fact, respond to information that’s much briefer than this, lasting less than a quarter of a millisecond.

In terms of sensing and then responding, a good measure is the sprinter reacting to the starting gun, which can be done in about 150 milliseconds. One limiting factor is how long it takes information to travel down our nerve pathways. In the 19th Century, Hermann von Helmholtz estimated this to be 35 metres per second, but we now know that some well-insulated nerves are faster, at up 120 metres per second.


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