What is a reaction time test?
A reaction time test measures the delay between a signal appearing and your response, in milliseconds. Simple reaction time uses one signal and one response; choice reaction time adds several possible signals, each with its own response.
WHERE THE MILLISECONDS GO · ROUGH, ILLUSTRATIVE SPLIT
~70 msEye to visual cortex
~60 msRecognise
~50 msDecide
~70 msMove
Light is converted by the retina and the signal reaches the visual cortex.Visual areas identify what appeared and where.Choosing the response; this grows with the number of options.Motor cortex sends the command and the finger moves the key.
THE TEST
Simple reaction
1Simple2Choice3Go / No-go
HICK'S LAW · 1952
Every doubling of choices adds the same delay
William Hick found that reaction time grows with the logarithm of the number of equally likely options. Going from 1 to 2 choices costs as much as going from 3 to 7. That's why your choice round was slower than the simple one.
288 mspredicted, illustrative constants
RT = 50 + 150 × log₂(n + 1)2001
2882
3503
3984
4385
4716
5007
5258
5489
56910
What scientists have timed
1850Nerves have a speedHermann von Helmholtz measured nerve conduction in frogs at about 27 metres per second, showing thought isn't instantaneous.
1868Subtracting decisionsFranciscus Donders compared simple and choice reaction times to estimate how long a decision takes.
1884Thousands of visitors timedFrancis Galton's Anthropometric Laboratory measured visitors' reaction times at the International Health Exhibition in London.
1952Hick's lawWilliam Hick showed reaction time rises with the logarithm of the number of choices.
KEEP GOINGTrain the reaction you just measured