What is reaction time?
Reaction time is the interval between a signal and your response to it. The signal can be a light, a sound or a touch. Because the interval is short, it is measured in milliseconds (ms), and 1,000 ms make one second.
The definition covers voluntary responses. An automatic reflex, like the knee jerk, takes a shorter route through the spinal cord and is a separate thing. The reflex test page explains that difference.
The stages of a reaction
A reaction feels instant, but it is a chain of steps.
- Detection. Your eye, ear or skin picks up the signal and turns it into a nerve signal.
- Recognition. The brain registers that something changed.
- Decision. The brain selects a response.
- Movement. A command travels down the spinal cord to the muscle, and the muscle contracts.
Most of the total is spent in the brain, not in the nerves. That is why anything that adds thinking, such as choosing between two buttons, makes the number larger.
Simple and choice reaction time
In a simple task there is one signal and one response. You know what will happen. You only do not know when. In a choice task there are several possible signals and each one needs its own response.
| Type | Example | Speed |
|---|---|---|
| Simple | Click when the panel turns green | Fastest |
| Choice | Press a different key for each color | Slower, and slower again with more options |
Hick’s law describes the pattern: the more options you have, the longer the decision takes. The test on this page is a simple reaction task.
How reaction time is measured
A measurement needs three things: a signal that starts at an unpredictable moment, a timer and several repeats.
Here the panel is red, then turns green after a random wait of about 1.5 to 5 seconds. You click, tap or press Space, and the timer records the gap. A click before green cancels that try and it is repeated, so guessing does not help.
You get five tries and the score is the average. Typical online results fall between 250 and 300 ms. Lab studies of young adults report about 200 to 250 ms, because lab equipment adds less delay than a home screen and mouse.
To see where your result sits, read the page on average reaction time.