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Brain exercise

How Long a Simple Decision Takes

Five goes at responding the moment a panel turns green, plus an honest account of why the number is rougher than it looks.

The gap between something happening and you responding to it is not one thing. It is light reaching your retina, a signal traveling to the visual cortex, a decision, a command to your hand, and muscle actually moving. All of that in roughly the time it takes to say the word.

Five trials. There is no score to beat and nothing is compared against anyone.

What just happened

Why we show you the middle value

  • Most of it is not thinkingDetecting the change and issuing the movement command takes up the bulk of the time. The deciding part is comparatively quick, which is why simple reaction times cluster so tightly across people.
  • Waiting is its own taskThe unpredictable delay before the panel turns green is deliberate. If you could anticipate it you would be timing a prediction rather than a reaction, which is why jumping early does not count.
  • Your five times differedVariation across trials is normal and expected. It is the reason a single go tells you very little and why the middle value of several is the only figure worth looking at.
Diagram from Chicago Brain Health breaking a simple visual reaction time into its stages, totalling roughly 250 milliseconds, with a note on the 30 to 80 milliseconds of noise added by browser measurement.
What a reaction time is actually made of

Averages are pulled around badly by one slow trial, and one slow trial is almost guaranteed in five. The middle value ignores the outliers and describes the run better.

Even then, be skeptical of the number itself. It is measured through a browser, on hardware we know nothing about, and that is a genuine limitation rather than a disclaimer for the sake of it.

Read the number loosely. Screen refresh rate, input device, and the browser’s own scheduling shift a figure like this by roughly 30 to 80 milliseconds. That is large compared with the differences people usually care about. A result here is a rough indication and not a measurement.

Square illustration from Chicago Brain Health showing a signal spreading outward from a green go point through the stages of a reaction, from retina to muscle.
From retina to muscle in about a quarter of a second

Science vs hype

What this does not mean

What you may have seen. Reaction time tests presented as a measure of brain age, of cognitive health, or of how sharp you are, often with a chart placing you against other people.

What this activity actually involves. A simple visual detection task, one of the oldest measurements in experimental psychology. This version runs five trials and reports the middle one.

Where the evidence stops. We show no percentiles, no norms and no interpretation, because none of those would be defensible from a browser on unknown hardware. Reaction time genuinely does vary with age, fatigue, caffeine and attention, but a five trial run in a web page cannot separate any of those, and a slow result here says nothing about your brain health.

A calm consulting room with two chairs set at an angle, prepared for a conversation
What an evaluation actually looks like: two chairs and a conversation

Who Can Use This One

  • Vision is required, along with the ability to make a quick hand movement. There is no audio version.
  • Timing is intrinsic here. A reaction time task cannot be made untimed without ceasing to be one, which is why this is the one exercise in the section with no untimed alternative. The explanation above is complete without running it.
  • Keyboard works, the space bar responds exactly as clicking does.
  • Nothing flashes. The panel changes color once per trial.
  • Nothing is recorded, and your times are gone the moment you leave the page.

What Real Measurement Looks Like

We showed you five numbers and then spent a paragraph explaining why you should not lean on them. That was not false modesty. Measured through a browser, on hardware we know nothing about, the noise is large enough to swamp anything worth knowing.

Real cognitive measurement is the opposite of this: standard equipment, controlled conditions, a trained person watching how you approach the task and not only what you score. That is what turns a number into an answer.

You have already done the curious part. If you would like to keep going and find out what is actually true for you, rather than what a browser can guess at, that is exactly what we do, and that conversation is free.

If you would rather read first, our conditions page sets out what neurofeedback is used for and how strong the evidence is for each, and our research page covers what the studies actually found, including the ones that came out negative.

Let’s chat

A free conversation with a psychologist. No intake form, no obligation, and we will tell you plainly when the answer is that you do not need us.

These activities are demonstrations of how perception, attention, memory and movement work. They are not tests, screenings or diagnostic tools, and no result here says anything about whether you have a medical or psychological condition. Nothing on this page is medical advice or a substitute for evaluation by a qualified professional. Last reviewed September 2026.