How Fast Is Fast? What Quick Reaction and Go/No-Go Actually Measure

Reaction time feels like it should be simple to understand: something appears, you respond, the clock stops. But two of Mentometry’s fastest-paced games, Quick Reaction and Go/No-Go, are built around a distinction that reaction-time researchers have studied for well over a century — the difference between simple reaction time and choice reaction time, and the even harder skill of knowing when not to react at all.

Quick Reaction is closest to what scientists call simple reaction time: a single, predictable stimulus appears, and your only job is to respond as fast as possible. Under laboratory conditions, healthy young adults typically respond to a simple visual stimulus in roughly 200 to 250 milliseconds. That number holds up remarkably well across studies, and it’s a useful benchmark — if your Quick Reaction times are consistently landing in that range, you’re performing in line with typical human visual reaction speed, which is itself an impressively fast feat of neural processing considering it involves light hitting your retina, several stages of visual processing, a decision, and a motor command reaching your hand.

Go/No-Go is a different, and in some ways more interesting, challenge. Instead of just reacting to everything, you have to react to some stimuli and deliberately withhold your response to others. This is a classic paradigm in cognitive psychology used to study what’s called response inhibition — the brain’s ability to stop an action that’s already been primed. It’s a core function of the prefrontal cortex, and it’s the same underlying mechanism that lets you stop yourself from blurting out a comment in a meeting or slamming the brakes when a light unexpectedly turns red rather than continuing on reflex. Performing well on Go/No-Go isn’t about being fast in a straight line — it’s about staying fast while also staying selective, which is a meaningfully harder combination.

Interestingly, research on both types of tasks has found that reaction time is influenced by more than raw neural speed. Fatigue, caffeine, time of day, and even mood measurably shift results session to session. This is actually a good reason to treat your Mentometry reaction scores as a snapshot rather than a fixed trait — if you play Quick Reaction first thing in the morning and again in the evening, don’t be surprised if the numbers differ meaningfully. That variability is normal and well documented, not a flaw in the test.

There’s also a well-known trade-off between speed and accuracy that shows up clearly in Go/No-Go: pushing yourself to react faster increases the chance of a false response on a “no-go” trial, while playing it safe slows your average time. Elite performance on the game isn’t about maximizing raw speed alone — it’s about finding the point where your reaction time is as fast as possible without your inhibition control breaking down.

Both games are quick enough to play as a five-minute break, and because reaction time is sensitive to your current state, they’re genuinely interesting to revisit at different times of day. Try Quick Reaction and Go/No-Go back to back on the Mentometry dashboard and see how the two numbers relate to each other — a large gap between them often says as much about your impulse control as it does about your speed.