Choice Reaction Time Test
Four colors, four keys. Your time with four keys is the score; the lag under it is what choosing cost.
The ladder
Bar widths show roughly how many people land in each band on the provisional curve. The ranked number is your four-key time, which only gets worse when you play worse; the lag under it says how much of it was the choosing.
What moves it
The number of choices. Hick's law: every doubling of the options adds a roughly constant slice of time. Four colors is two doublings past one.
Practice. The key mapping gets automatic fast. A first run carries the cost of remembering which key is which; a tenth run mostly does not.
Your hardware, in the time but not in the lag. A slow screen or a laggy touchscreen adds the same milliseconds to both rounds. Your four-key time carries them, like the reaction-time test does; the lag under it subtracts them out.
What this measures
A choice reaction test adds the one ingredient the simple test leaves out: a decision. Four colors each demand their own key, so before your hand can move, your brain has to identify what it saw and select which response belongs to it. That selection has a price, it grows at a roughly constant rate per doubling of the options (Hick's law, 1952), and this page is built to show you your own price as a number.
Round one is your baseline: eight flashes, answered with any key, your plain reaction speed on this screen with this hand. Round two turns the choosing on: sixteen flashes in four colors, answered on D F J K or the four buttons, every answer labeled with its color's name so hue is never the only cue. The score is the four-key average. The decision lag under it is round two minus round one: what the choosing cost, with your hardware's share subtracted out, since it rides both rounds equally.
Wrong keys are excluded from the mean and counted beside it, a tap before the flash is discarded, and 1.5 seconds of nothing is scored as asleep and the tap repeated. One pool for everyone, phone or keyboard; the Method page declares the starting curve and the runs measured so far.
Questions people ask
Because a difference can be gamed: play the one-key round slowly and the lag shrinks, down to nothing. The four-key time only gets worse when you play worse, so it is the number that ranks you. The lag is still here, one line down: it is the part four choices added, and the interesting one to compare across days.
On the provisional curve, 500 ms is the middle and under 400 ms is quick; about 200 ms of a typical time is the choosing. The number is derived, not measured: the site switches to its own distribution as runs accumulate, and everyone plays in one pool, so expect a first run to sit above a practiced one.
Yes, on a noisy day: eight one-key taps is a small sample, and two slow ones lift the baseline above the four-key mean. A negative lag is not a superpower, it is a wobbly baseline, and it does not change your score. The two practice taps and the 1.5 second lapse rule exist to keep the wobble small.
Because that is where resting fingers already sit: two keys under each hand, no travel, and the mapping printed on every flash. The test wants to measure your choosing, not your hunting. On a touch screen the four labeled buttons do the same job, and the label always carries the color's name, so the answer never depends on telling hues apart.
It starts as an assumption worth 300 runs, shaped from published norms, and every run played here adds one to it, everyone in one pool. The Method page says which norms, how the percentile is read, and how many runs this test has measured so far.