Reaction time is the time between a stimulus and the appropriate voluntary response – usually in milliseconds. It bundles three steps: perceiving the stimulus, processing and deciding, and triggering the muscle response. That's why reaction time is a good summary indicator of sensorimotor coordination and alertness.

As early as 1868, Franciscus Donders showed: the simple reaction (one stimulus, one response) is fastest, the choice reaction (several stimuli, several responses) slowest – with the discrimination / "go-stop" task in between. Individual mental steps can be estimated from the time differences (subtraction method).

The more options, the slower the response – that's Hick's law. The typical guide value for a simple visual reaction is roughly 200–250 ms.

Source: Donders, F. C. (1969). On the speed of mental processes. Acta Psychologica, 30, 412–431. (Originalarbeit 1868) · Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4(1), 11–26.

Reaction time is present in many everyday moments: catching the glass that's about to tip over, braking at the wheel for a sudden obstacle, taking a step in time when you stumble, turning off the stove when something boils over. It is closely linked to attention, processing speed and fine motor skills.

From around the age of 20 the reaction slows, and the decline accelerates after 60. A slower processing speed is associated with a higher fall risk; in a study of older people with sarcopenia, every additional millisecond of reaction time was associated with roughly 1.5 % higher fall risk.

The good news: processing speed can be trained. Reaction and speed training are considered a sensible building block – including in fall prevention.

Source: Kilaitė, J., Dadelienė, R., Ginevičienė, V., et al. (2025). Psychomotor speed and fall risk in older adults with sarcopenia and frailty: a cross-sectional study. Medicina, 61(4), 706. · Lord, S. R., & Fitzpatrick, R. C. (2001). Choice stepping reaction time: a composite measure of falls risk in older people. The Journals of Gerontology: Series A, 56(10), M627–M632. · Okubo, Y., Schoene, D., & Lord, S. R. (2017). Step training improves reaction time, gait and balance and reduces falls in older people: a systematic review and meta-analysis. British Journal of Sports Medicine, 51(7), 586–593.

Behind almost all the tests here lies the same question: how well does your brain steer your own behaviour when a situation is new or an automatic impulse gets in the way? These control abilities are called executive functions – something like the management floor of thinking, located in the frontal lobe.

Research usually groups them into three core building blocks:

• Impulse control (inhibition): braking an automatic or tempting impulse and staying on task – not dashing off just because the signal briefly flashes.
• Working memory: holding information briefly in mind and working with it – like a mental notepad, e.g. when you remember directions while walking.
• Cognitive flexibility: switching between tasks or rules and adjusting to the unexpected, instead of sticking to the old pattern.

From these three arise the "bigger" abilities such as planning, problem-solving and anticipatory action.

What this has to do with everyday life: impulse control is the moment you leave the phone alone and stay on task – or pull your foot back at the crossing because a car is coming after all. You need working memory when you remember why you went into a room, or keep a recipe step by step in mind. Cognitive flexibility helps when a plan falls through and you have to reschedule. These abilities are central to everyday life, school and work – and especially valuable in later life, because being able to do things simultaneously (walking while thinking, a dual task) is closely linked to balance and fall risk.

Why this matters in the Stroop test: in the colour & word mode one building block becomes especially visible – impulse control. Reading runs so automatically that it interferes with naming the colour; the conflict can only be resolved by the executive control actively braking the automatic reading impulse. That is exactly why the Stroop test is regarded as a classic "window" onto this ability. The go/stop mode demands the same brake, choice reaction and reactive step more the fast deciding and switching, and the memory mode working memory. This is meant as illustration – the tests remain a game and do not measure any "brain performance".

Source: Diamond, A. (2013). Executive functions. Annual Review of Psychology, 64, 135–168. · Miyake, A., Friedman, N. P., Emerson, M. J., Witzki, A. H., Howerter, A., & Wager, T. D. (2000). The unity and diversity of executive functions and their contributions to complex „frontal lobe“ tasks: A latent variable analysis. Cognitive Psychology, 41(1), 49–100.

Balance runs on two levels: anticipatory (adjustments before an expected disturbance – e.g. tensing before lifting a heavy box) and reactive (compensatory adjustments when something unexpected happens – the bus brakes, you slip). Reactive reactions run via sensory feedback from the eyes, the vestibular sense and proprioception.

For small disturbances the ankle strategy suffices, for larger ones the hip strategy. If neither is enough, the "base-of-support" reactions come in: a stepping response or grasping for support. These stepping and grasping reactions are crucial to preventing falls. In timing they lie between the very fast reflexes and the slower voluntary movement (long-latency reflex loops with cortical involvement).

An established clinical test is the Choice Stepping Reaction Time: stepping onto a randomly lit field as fast as possible. People with a history of falls take considerably longer than fall-free people (in the original study around 1322 ms versus 1168 ms) – the test predicts future falls independently. Important: whole-body steps take longer than a keypress; in the game we train the decision and direction component, not the whole step.

Targeted perturbation-based balance training (controlled "pushing off balance") is particularly effective for reactive balance; individual programmes roughly halved fall rates over 6–12 months. This is precisely a core topic in physiotherapy – and the reason this mode is in here.

Source: Horak, F. B. (2006). Postural orientation and equilibrium: what do we need to know about neural control of balance to prevent falls? Age and Ageing, 35(Suppl 2), ii7–ii11. · Maki, B. E., & McIlroy, W. E. (1997). The role of limb movements in maintaining upright stance: the „change-in-support“ strategy. Physical Therapy, 77(5), 488–507. · Mansfield, A., Wong, J. S., Bryce, J., Knorr, S., & Patterson, K. K. (2015). Does perturbation-based balance training prevent falls? Systematic review and meta-analysis of preliminary randomized controlled trials. Physical Therapy, 95(5), 700–709.

Reading is so well practised that it runs almost automatically. If the colour word "RED" appears in blue type, the brain reads "red" first – and that response has to be actively suppressed in order to name the actual ink colour. That is exactly what takes time.

The effect is named after John Ridley Stroop (1935): with conflicting (incongruent) colour words, responses are slower and more error-prone than with matching (congruent) ones. The difference between the two – reported in the result as "interference" – shows how much effort resolving the conflict costs.

The test is regarded as a measure of selective attention, cognitive control and the ability to brake an automatic impulse – i.e. impulse control, one of the core executive functions (see section above). In everyday life it's the same ability with which you separate what matters from distraction and don't fall for the first reflex. Here too: pure trying out, no diagnostics.

Source: Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. · MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163–203.