Brain and reaction tests
How reaction-time, memory-span, Stroop and "brain age" tests work, what each really measures, and how a short night quietly wrecks the scores.
These tests are for interest and self-awareness, not a clinical cognitive assessment. Scores swing with sleep, caffeine, stress, practice and your device. Persistent or worsening problems with memory, attention or thinking deserve a doctor's assessment.
What these tests really show
Quick brain tests are genuinely fun, and they can teach you something useful — but usually not what they claim. Each one measures a narrow ability: how fast you react, how much you can hold in mind, how well you can override an automatic response. None measures intelligence, and every one of them is dominated by a single everyday factor: how alert you are.
That makes them a surprisingly good mirror for sleep. Take the same test well-rested and after a short night, and the drop is often startling — a more honest demonstration of sleep debt than any lecture. Each guide below explains one test and what tiredness does to it.
The tests
Reaction time
How fast you respond to a signal — the score most sensitive to tiredness.
Memory span
How many items you can hold in mind at once — a window on working memory.
The Stroop test
Name the ink colour, not the word — a neat measure of attention and mental control.
"Brain age" tests
A fun score that bundles several quick tasks — take the number with a large pinch of salt.
Source: General cognitive-psychology references on reaction time, working memory and the effects of sleep loss on performance. · checked 2026-09-04
Frequently asked questions
Do these tests measure intelligence?
No. They probe narrow slices — reaction speed, working memory, attention control. They are not IQ tests, and a single score on a tired evening tells you little on its own.
What is the biggest thing that changes my score?
For most people it is sleep, followed by caffeine, stress and practice. That is the running theme here: alertness drives performance more than raw ability.
Are brain-training games worth it?
You mostly get better at the games, with limited carry-over to daily life. For long-term brain health the evidence favours sleep, physical activity, social contact and heart health.
See your sleep debt, not just your score
TempoLife tracks your sleep and estimates the debt that slows your reactions and focus.