Reaction Time and Focus: Averages, the Stroop Effect and More

Reaction time is the interval between a signal and your response to it. In a simple reaction time task there is one signal and one response, such as tapping as soon as the screen turns green. In a choice reaction time task you must pick the right response from several, such as pressing a different key for each colour.

Even a simple response involves several stages: your eyes and brain have to detect the change, you have to decide that it is the signal you were waiting for, and the command has to travel to the muscles of your hand. Choice tasks add a decision stage, so they are slower. A classic finding known as Hick's law (Hick, 1952) describes how choice reaction time increases as the number of possible options grows.

In laboratory conditions with specialized equipment, simple visual reaction times for young adults are typically in the range of roughly 200 to 250 milliseconds. Responses to sounds tend to be slightly faster than responses to lights. Reaction times gradually lengthen with age, and they also vary a lot from one attempt to the next, even for the same person.

Because single trials are noisy, it is better to look at several attempts together. Using the median, the middle value, is a common choice because one slow trial where you blinked, or one lucky early tap, has little effect on it.

When you test reaction time in a browser, the result includes more than your nervous system. A typical screen refreshes 60 times a second, so a new image can take up to about 17 milliseconds just to appear. Displays also add their own processing time, touchscreens sample input at intervals, the browser needs time to register the tap, and wireless keyboards or mice can add further delay.

Together, these steps often add tens of milliseconds, which is why browser-based results commonly land somewhat higher than lab figures, often in the region of 250 to 300 milliseconds or more on typical phones and computers. The practical lesson is to compare results on the same device and to avoid drawing conclusions from small differences between devices.

In 1935, John Ridley Stroop published a now famous experiment. People were asked to name the ink colour of colour words, and they were much slower when the word and ink did not match, such as the word RED printed in blue, than when they did. This slowdown is called the Stroop effect.

The effect happens because reading is highly automatic for fluent readers. The meaning of the word arrives almost without effort and competes with the colour you are trying to name. Overcoming that competition draws on attention control, sometimes called inhibitory control: the ability to stay focused on the goal and hold back a strong but unhelpful response.

That is why Stroop-style tasks are widely used in psychology as a measure of focus. A useful score looks at both speed and accuracy, because you can always go faster by making more mistakes, or be more accurate by slowing down. Good attention control shows up as staying both quick and correct on the mismatched items.

Sleep has a large effect. After a short or poor night, reaction times tend to get slower and, just as importantly, less consistent, with occasional lapses where you respond very late or not at all. Attention control also suffers when you are tired.

Caffeine can improve alertness and reaction time, particularly when you are fatigued, although the effect varies between people and regular users may notice less of a boost. It does not replace sleep. Practice helps too: people get faster as a task becomes familiar, and Stroop interference often shrinks somewhat with practice, although it rarely disappears.

Mood, motivation, time of day and distractions all play a part as well. This is ordinary day to day variation. A single slow result is not a sign that anything is wrong, and these tests are not designed to assess health.

The free Witprism reaction and focus test takes about two minutes. First you tap the moment the screen turns green over five trials, with an unpredictable wait each time so you cannot anticipate it. Then you name the ink colour of 16 colour words, half matching and half mismatched. You get your median reaction time, a focus score that combines speed and accuracy, and an overall score on the 100 and 15 scale.

For the fairest result, use the same device each time, close other apps, sit somewhere quiet and do a practice run if you like. Treat any one session as an estimate, and if you want to see how sleep or caffeine affect you, compare several sessions taken under similar conditions.