Go/No-Go Test

This task gives you a speed number and an error number, and they pull against each other. Three out of every four squares are green, so pressing quickly turns into a habit. The faster you get, the more often that habit fires on a red square.

Those wrong presses are called commission errors. They are the number most researchers actually care about.

Read the pair together. Six errors with a 340 ms average is a different person from zero errors with a 470 ms average. Neither is better. They describe where you set the dial between speed and control, and that setting is steady enough within one person to be worth knowing.

If green and red turned up equally often there would be no habit to break. The test would sink into an ordinary two-choice reaction test.

The imbalance is the whole design. Common green squares build the habit. Rare red squares then have to interrupt it. The strength of that habit is what makes your errors mean something instead of being random.

Each square stays on screen for 750 ms, with 1000 ms between squares. Both numbers matter. Make the window shorter and everyone makes more errors. Make it longer and the task stops being hard. Another site will use different timings, so its scores are not comparable with these.

This task and its close relatives are the standard laboratory way to measure how well someone can stop a movement they have already started. Researchers use them in work on attention, addiction and impulse control.

What they measure is narrow. It is the ability to cancel a movement you are already committed to, within a few hundred milliseconds.

Everyday impulsiveness is much wider than that. It involves planning, reward, patience and mood, and it only loosely tracks this task. A poor score here does not point to ADHD or anything else. A clean score rules nothing out. Diagnosis needs a clinician, your history and tools built for the job. For what happens to control when a task is dull rather than fast, see the sustained attention test.

Do not slow down on purpose to protect your error count. The task only tells you something if you are honestly trying to be fast. A cautious run gives a flat, useless result. Aim to be quick and accept that some red squares will catch you.

Expect the second half of a run to be worse than the first. That drift is real, and it is the same effect the psychomotor vigilance task is built to expose. Run 80 trials and watch where the errors bunch up.

Your go time here will be slower than your simple reaction time, because a decision sits in the middle of it. Average reaction time by age gives the population picture for the simpler task. What counts as a good reaction time explains why the two numbers cannot be swapped.