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What Affects Reaction Time? 8 Factors That Matter

Updated

Play this game on two different days and your average can easily move by 30 to 50 milliseconds. That swing isn't random. How rested you are matters, and so does what you've had to drink, whether you can predict the signal, and even the screen in front of you. Some of these you control. Others you just have to live with.

1. Sleep

Sleep matters more than anything else on this list, and the research on it is a little alarming. In a well-known 2003 study, Hans Van Dongen and colleagues limited healthy adults to 4, 6 or 8 hours in bed a night for 14 days. Six hours or less produced deficits in thinking and reaction speed equivalent to up to two full nights without sleep. The participants' own sleepiness ratings suggested they had little idea how impaired they'd become.

One of the main measures in that study, the Psychomotor Vigilance Task, works a lot like this game: wait for a signal, respond as fast as you can, repeat.

2. Caffeine

Caffeine reliably improves alertness and reaction time, and the effect is strongest when you're tired. Reviews of the research find benefits from moderate doses, roughly what's in a cup or two of coffee. Heavy daily coffee drinkers may notice less of a lift, and it fades as the caffeine wears off over a few hours.

3. Alcohol

Alcohol slows reactions and makes them less consistent, even at levels where people feel fine. On the road that means a longer gap between seeing a hazard and braking, which is where much of the danger of drink-driving comes from. Reaction time and driving covers what that gap costs in metres, and why a phone conversation can be even worse.

4. Predictability

If you can predict when a signal will arrive, you get faster, because your brain starts preparing the movement before the signal appears. Psychologists call this the foreperiod effect. A fair test removes it by making the wait unpredictable. On this site the server picks a random delay before every target, so there's no rhythm to lock onto.

5. The kind of signal

Most people react faster to sounds than to things they see. Lab studies typically put responses to a simple tone a few tens of milliseconds ahead of responses to a light. Having to choose also slows you down. Reacting to "red means left, blue means right" takes longer than reacting to a single target, and every extra option adds a little more time, as explained in simple versus choice reaction time.

6. Practice and warm-up

Almost everyone's first few games are their slowest. Scores climb quickly with practice and then level off. Part of that is learning the test and part is plain warming up, as concentration and hand speed both sharpen after a minute or two. Whether video games give you a lasting boost is a more contested question, covered in do video games improve reaction time?

7. Age

Simple reaction time is surprisingly stable through adulthood. One study of more than 7,000 UK adults found little slowing until around age 50, though more complex reactions slow earlier. The full picture is in reaction time by age.

8. Your equipment

An online reaction test measures you plus your device. A 60 Hz screen only refreshes every 16.7 ms, so a target can wait up to that long before it's even drawn. Touchscreens, wireless mice and TVs that aren't in game mode can each add more on top. Two people with identical reflexes can easily end up 30 ms apart on different devices. The whole chain is explained in how online reaction tests work.

Getting your true best score

Play when you're rested rather than late at night, and warm up with a couple of games before you go for a record. Use the quickest setup you have, which usually means a computer with a wired mouse and a high refresh rate screen. Keep your eyes on the middle of the arena so you never have to hunt for the target. And resist the urge to guess: anything under 100 ms counts as a false start and the round restarts.

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