What Is Reaction Time?
Reflex Lab · foundational explainer
Reaction time (RT) is the delay between a stimulus and a response. In everyday terms: how long after something happens do you start acting?
Simple vs choice reaction time
Simple RT uses one signal and one allowed response (our Reaction Time Test). Choice RT adds decisions — for example, respond only to green, ignore red. Choice RT is slower because the brain must classify the stimulus before committing motor output.
How reaction time is measured
Labs use calibrated displays and response devices. Browser tests use performance.now() (or similar) between paint/signal and pointer/keyboard events. They are excellent for personal tracking and education, but they include input-device and display latency.
Why RT changes with fatigue
Sleep debt, long sessions, and divided attention often lengthen average RT and increase variability (spread). A single slow trial is noise; a slower average with wider spread across a set often means attention dipped.
Reaction time vs accuracy
Faster is not always better. In tasks with penalties for wrong responses, rushing raises error rates. Games that mix “go” and “no-go” targets (for example bombs in Focus Drop) intentionally train that tradeoff.
Limitations of browser tests
A browser RT tool cannot replace a lab setup. Display refresh, input-device latency, background tabs, and OS scheduling all add noise. Use the result to compare yourself across days — rested vs tired, full-screen vs tiny window — not as a clinical score.
Next: Speed vs accuracy · Related: Attention under load.