Reaction-Time
Variability Instrument

Go / No-Go · Ex-Gaussian

A browser implementation of the sustained-attention paradigm used in attention research. It records every response to sub-frame precision and decomposes your reaction times into the three parameters that matter — not just an average, but the consistency of your responding and the rate of attentional lapses.

The task

K
A letter flashes in the centre. Press SPACE as fast as you can for every letter…
X
…except X. When you see X, do nothing — hold your response.

Most trials are “go”, so the rhythm pulls you toward pressing automatically. The rare X is where impulse control shows up. On a phone, tap anywhere instead of SPACE.

Session length
Advanced timing parameters
Find a quiet moment. Timing fidelity depends on a focused, single-tab environment.

This is a research-style measurement instrument and an educational demonstration — not a medical or diagnostic device. A single session is noisy, the scores overlap heavily with the general population, and stimulants improve these measures in people with and without ADHD alike. Nothing here can confirm or rule out a condition or guide medication decisions; that's a clinician's job.

Sustained attention · Go/No-Go

Reaction-Time Variability

What this test measures

This is a go/no-go task: letters flash by, you respond to every one except X, and you withhold the response when X appears. Because responding is easy and frequent, the interesting signal is not whether you can do it but how consistently — moment-to-moment fluctuations in reaction time are one of the most robust behavioural markers of lapses in sustained attention, and elevated reaction-time variability is among the most replicated findings in ADHD research.

Rather than reporting a single average, the task decomposes your reaction times ex-Gaussian style into speed, consistency, and the lapse tail (τ) — the occasional very slow responses that an average hides. Failing to withhold on X (commission errors) additionally indexes response inhibition.

How to use it

A session takes a few minutes and needs no strategy. Attention state — sleep, time of day, stimulation — moves these numbers, which is what makes the task useful for tracking. Signed-in sessions feed the Go/No-Go trend on the Progress page.

Sapiens Bench tasks are educational instruments for self-tracking, not medical or diagnostic devices.