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What Affects Reaction Time — Age, Sleep, Caffeine and Fatigue
How age, sleep deprivation, caffeine, fatigue and general condition change reaction time, based on research findings.
Even for the same person, reaction time varies from day to day and hour to hour. Here are the factors that research has confirmed relatively well.
Age
Der & Deary (2006) analyzed reaction time data from the UK Health and Lifestyle Survey (7,130 adults aged 18–94). Simple reaction time barely slowed until around age 50 and slowed after that, while choice reaction time slowed steadily throughout adulthood. In this sample, women's reaction times were slightly slower and more variable than men's.
With age, not only the average but also the trial-to-trial fluctuation (variability) tends to increase. That's why this site also shows the standard deviation.
Sleep deprivation
Van Dongen et al. (2003) restricted sleep to 4, 6 or 8 hours a day for two weeks and reported that even people who kept sleeping 6 hours showed progressively worse performance on an attention task (PVT), falling to a level similar to staying up all night. Especially important was that the participants didn't feel correspondingly sleepy.
When you're short on sleep, occasional very slow trials (attention lapses) increase before your average reaction time does. If you often get one or two unusually slow values within a set, it may be a sign of fatigue.
Caffeine
A review by McLellan et al. (2016) concluded that moderate amounts of caffeine improve alertness, attention and reaction time, with the effect especially clear when sleep-deprived. However, individual differences are large, and drinking more doesn't keep increasing the effect.
Fatigue, condition and environment
- Warm-up — The first few trials are usually slower. Discarding one set as practice gives more stable results.
- Posture and readiness — Resting your finger on the button and looking at the center of the screen shortens the movement and perception stages.
- Distractions — Notifications, conversation and background noise scatter your attention, increasing omissions and slow trials.
- Time of day — Your condition varies through the day with your circadian rhythm. When tracking your trend, it's best to measure at a similar time of day.
What you can do with this test
By measuring on the same device under different conditions — before and after sleep, coffee or exercise — you can see which factors affect you most. However, this test is not a medical diagnostic tool.
Sources
- Der G., Deary I. J. (2006) Age and sex differences in reaction time in adulthood. Psychology and Aging 21(1):62–73
- Van Dongen H. P. A. et al. (2003) The cumulative cost of additional wakefulness. Sleep 26(2):117–126
- McLellan T. M., Caldwell J. A., Lieberman H. R. (2016) A review of caffeine's effects on cognitive, physical and occupational performance. Neurosci Biobehav Rev 71:294–312