Reaction Time Test

What is reaction time?

Reaction time (RT) is the interval between a stimulus appearing and you responding. It is the most basic measure in cognitive psychology - dating to Franciscus Donders' 1868 experiments - and is still one of the most informative. Modern researchers distinguish:

• Simple reaction time (SRT): one stimulus, one response. "Click as soon as the screen turns green." Average adult: 200 to 250 ms.
• Choice reaction time (CRT): multiple possible stimuli, each with its own response. "If it is green, click left; if red, click right." Average adult: 350 to 500 ms.
• Go/No-Go: respond to some stimuli, withhold response to others. Adds an inhibitory load. Average: 400 to 550 ms.

The gap between SRT and CRT is the time required for decision-making. Hick's Law, formulated in 1952, says CRT increases logarithmically with the number of choices - about 150 ms per doubling. The slope of this relationship varies between individuals and correlates with general cognitive ability.

Reaction time and intelligence

The link between RT and IQ has been studied for over 130 years, since Francis Galton's anthropometric laboratory began collecting reaction times in 1884. Modern meta-analyses are consistent: simple reaction time correlates with IQ at about -0.2; choice reaction time at about -0.4 (negative because faster RT goes with higher IQ).

The more interesting finding is that the variability of reaction time matters more than its average. Two people can have identical mean RT, but the person whose RTs cluster tightly around the mean tends to be more intelligent than the one whose RTs are scattered. This is the basis of mental speed theory: high-IQ individuals are not necessarily faster, but they are more consistent - their cognitive systems are less subject to noise and lapses.

That said, the RT-IQ correlation is moderate. RT alone is not a useful proxy for IQ, and many high-IQ individuals have unremarkable reaction times. Use RT as one signal among many, not as a stand-alone measure of ability.

What is a good reaction time?

For a browser-based simple reaction test (click when the screen changes color), here are rough benchmarks for adults:

Caveat: browser RT tests include monitor lag (typically 10 to 30 ms for 60 Hz, less for 144 Hz+), browser frame timing, and mouse input delay. Absolute values are noisy. Differences over time on the same hardware are meaningful; comparisons between people on different setups are not.

What changes your reaction time

RT is one of the most state-sensitive cognitive measures. Common modifiers:

• Sleep deprivation: +50 to +100 ms after one bad night; +200 ms after two
• Caffeine: -10 to -30 ms within 30 to 60 minutes (peak), if you are not already caffeine-tolerant
• Alcohol: +50 ms per 0.05% BAC, and impaired even at sub-impairment doses
• Age: RT increases about 1 ms per year from age 25 onward, accelerating after 60
• Practice and gaming: regular action-game players show RTs 30 to 60 ms faster than non-players
• Mood: depression slows RT, anxiety can speed it slightly but increases variability and errors

Try reaction-time exercises now

How reaction time fits in your cognitive profile

RT is not part of the standard WAIS-IV battery (which is paper-and-pencil), but it is heavily used in cognitive neuroscience and in occupational testing for pilots, drivers, surgeons, and elite athletes. Our full IQ test does not measure raw RT, but the test's processing speed subscore is closely related and is often informative if your RT is unusually fast or slow.

Important caveats

Single-trial browser RT tests have wide measurement error. Run 20+ trials to get a stable average. Account for hardware: a 60 Hz monitor adds 8 to 17 ms of unavoidable latency; a wireless mouse adds 5 to 15 ms over wired; high-end gaming setups can be 30 to 50 ms faster than office hardware for identical biological speed. Test multiple times under similar conditions before drawing conclusions.