What Is Reaction Time?
Reaction time is the interval between the onset of a stimulus and the beginning of a response. It represents the time your nervous system needs to perceive a signal, process it, and initiate a motor response.
In everyday terms: the time between seeing a red light and pressing the brake pedal. Between seeing a ball and swinging to hit it. Between noticing a car swerving and turning your wheel.
Types of Reaction Time
Simple reaction time: One stimulus, one response. A light turns on; you press a button as fast as possible. This measures basic neural processing speed.
Choice reaction time: Multiple stimuli, multiple responses. Press button A if the light is red; press button B if it is green. Slower because the brain must identify the stimulus before selecting the response.
Discrimination reaction time: Respond to a target stimulus but not to distractors. Even slower than choice reaction time.
Most real-world reactions are choice or discrimination reactions, not simple reactions.
Average Reaction Times
For simple reaction time tasks (press a button when a light appears):
| Group | Average reaction time |
|---|---|
| Young adults (18–30) | 190–240 ms |
| Middle-aged adults (30–50) | 230–280 ms |
| Older adults (60+) | 280–350 ms |
| Elite athletes | 150–200 ms |
| Top-level sprinters (starting gun) | 140–160 ms |
For auditory stimuli, reaction times are about 20–30 ms faster than visual – the auditory pathway to motor cortex is shorter. This is why the starting pistol (sound) produces faster sprinter responses than a starting light.
What Slows Reaction Time
Age: Reaction time increases approximately 15% per decade after age 30, mainly due to slowing of neural conduction velocity and cognitive processing speed.
Fatigue and sleep deprivation: Even 17 hours without sleep produces reaction time impairment equivalent to 0.05% blood alcohol concentration.
Alcohol: Well-documented. At the legal driving limit in many countries (0.05–0.08% BAC), reaction time increases by 15–30%.
Mobile phone use while driving: Handheld phone use increases reaction time by 30–50%. Hands-free calls: 15–20% slower (the cognitive distraction, not the hand position, is the main factor).
Caffeine: Mild improvement in simple reaction time (40–60mg caffeine reduces reaction time by ~10ms). Effect is larger for fatigued subjects.
Cold: Finger temperature below ~20°C slows manual response time. Relevant for winter sports.
What Improves Reaction Time
Physical fitness: Aerobic exercise is associated with faster reaction times, likely through improved cerebrovascular health and neural efficiency.
Sport-specific training: Athletes in fast-reaction sports (table tennis, boxing, badminton) develop faster reactions to domain-specific stimuli. The improvement is partially stimulus-specific – a boxer's improved reaction to a punch does not fully transfer to pressing a keyboard button.
Video games: Action video game players demonstrate faster and more accurate responses in laboratory reaction time tasks. The effect is real but modest for cognitive (not domain-specific physical) stimuli.
Practice: Repetition reduces reaction time for familiar stimuli. Experienced drivers respond faster to traffic hazards than new drivers – partly because they recognize patterns earlier.
Sleep and recovery: Being well-rested is one of the most reliable ways to maintain near-optimal reaction time.
Testing Your Reaction Time
The Reaction Time Test on this site measures your simple visual reaction time across multiple trials. Click when the colour changes, and it reports your average, best, and worst reactions with a comparison to published norms.
A few practical notes for valid testing:
- Use a mouse click, not a touchscreen tap (some latency difference)
- Run 10+ trials for a reliable average
- Expect your first trial to be slower as you calibrate to the task
- Test when well-rested for your baseline; test when fatigued to see the difference
Summary
Average simple reaction time for young adults is around 200–240 ms. It slows with age, fatigue, alcohol, and distraction. Sport-specific training and aerobic fitness improve reaction time. For daily life, being well-rested and minimising distractions (especially phone use while driving) has far more impact than any dedicated reaction time training.