A box changes colour and you click. The page shows a number in milliseconds. It looks like a direct reading of how fast your mind works, but that number is really the sum of several small steps, and not all of them happen in your head.
What happens in that fraction of a second
Four things stack up between the signal and your click.
First, the change has to appear on the screen, and the screen takes a moment to draw it. Then your eyes pick it up and your mind registers that this is the signal. In a simple test there is nothing to decide, only “now”. Finally your finger moves and the press is recorded.
Only the middle part is what most people would call thinking. The rest is eyes, muscles and hardware. A typical simple reaction in a browser lands around a quarter of a second, and a good share of that is wiring and machinery.
Key idea
Your result shows how quickly you responded on this device, on this try. It isn’t a measure of how smart you are.
Simple and choice reaction time
In 1868 the Dutch scientist Franciscus Donders had a clever idea. Time how long a person takes to react to one signal. Then time how long they take when there are several signals, each needing a different response. The extra time in the second task, he reasoned, is the cost of deciding.
Later work by Hick and Hyman in the early 1950s added a pattern that still holds up well. More options make people slower, but not in a straight line. Each time the number of options doubles, the delay grows by a similar slice. Going from two choices to four costs about the same as going from four to eight.
Our reaction time test is the simple kind: one signal, one response, nothing to weigh up.
Why your score moves between tries
Researchers who reviewed the factors behind simple reaction time found a long list. A few matter most for an online test.
- Practice. The first tries are usually slower, because you are still learning the task. Times tend to improve and then level off.
- Alertness. Tired or distracted people respond more slowly, and they vary more from try to try.
- The kind of signal. Studies comparing the two usually find that people respond to a sound a little faster than to a light. A screen test uses light.
- Your equipment. Screen refresh rate, a mouse or a touchscreen, a wireless connection: each can add delay that isn’t yours.
- Anticipation. Click before the signal appears and you are guessing, not reacting. A fair test throws those tries out and asks you to go again.
Reading your five tries
Look at the whole set, not one number. A common pattern is a slower first try, then a cluster of similar times. One much slower try usually means your attention slipped for a moment, or the page hiccuped. A very steady set tells you something about that session. A bumpy set tells you less than it feels like it does.
If the times are all over the place, check the basics. Are you rested? Using the same finger? Is the page in the foreground? Then try again.
Getting a steadier number
If you want a result you can trust a little more, keep the conditions the same. Use one device and the same way of clicking, and take the test when you feel rested. Rest your finger on the key so it is ready. Treat the first one or two tries as warm-up, then look at the overall picture instead of the single best number.
Comparing your score with a friend’s is another trap. A friend on a different phone or a different screen is measuring something slightly different.
Why people care about reaction time
Researchers like it because it is simple to measure and the stages are easy to separate. Gamers and athletes like it because quick responses are fun to chase. But a click test is a long way from driving or a match, where you also have to decide what to do, and decisions add their own time.
What it can’t tell you
A reaction time test says nothing about intelligence, about how good a driver you are, or about how fast you think in general. It records one narrow response on one day. A quick result doesn’t promise quick thinking elsewhere, and a slow one is not a problem.
For the wider picture on reading any test result, see what psychology tests can and can’t tell you. And if you’re curious about staying focused over a longer stretch, there’s a piece on attention span.
Keep reading
What psychology tests can and can't tell you
A plain guide to reading any online psychology test: what a result shows, what it leaves out, and how to use it without taking it too seriously.
Attention span: myths, and what helps
No, you don't have a goldfish's attention span. What research says about how focus drifts, why it dips over time, and small habits that help.
Questions
What is a good reaction time?
There isn't one number that counts as good. A simple reaction to a change on a screen usually lands around a quarter of a second, and your screen, device and alertness all add or remove a little. Our bands are only a guide for reading your own result.
Why is my reaction time different every time?
Early tries are often slower while you work out the task. Tiredness, distraction and the device you use also change the number from try to try, so look at the pattern across several tries.
Can you improve your reaction time?
A little. Most people speed up over the first few tries as the task becomes familiar, then level off. Being rested and alert helps. Beyond that, the gains are small.
Sources
- Woods, D. L., et al. (2015). Factors influencing the latency of simple reaction time. Frontiers in Human Neuroscience.
- Jain, A., et al. (2015). A comparative study of visual and auditory reaction times. International Journal of Applied and Basic Medical Research.
- Donders, F. C. (1969). On the speed of mental processes (W. G. Koster, Trans.). Acta Psychologica, 30, 412–431. (Original work published 1868.)
- Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology.
- Hyman, R. (1953). Stimulus information as a determinant of reaction time. Journal of Experimental Psychology.
For learning and self-reflection, not medical advice.