When you voluntarily press a button, your brain shifts the perceived timing of both the action and its effect — the action feels like it happened slightly later than it did, and the effect feels like it arrived slightly earlier. The gap between them compresses.
This is intentional binding (Haggard et al. 2002). The effect only occurs for voluntary movements. TMS-induced involuntary movements produce the opposite: action shifts earlier, effect shifts later, gap widens. The same physical sequence; opposite distortion.
This simulation uses the Libet clock: a hand that completes one revolution every 2.5 seconds. You'll watch it, press a button when you choose, and then report where the hand was at each moment. The gap between your reports and the actual record is the binding effect.
The simulation measures your reported positions on a fixed clock face — but it can't tell you whether your perception shifted, or whether you simply misremembered when asked to reconstruct. Intentional binding experiments distinguish these by varying delay and instruction conditions; this version doesn't have the trial count or controls to separate them.
The known effect sizes (action: ~50ms later, effect: ~40ms earlier) are averages across many subjects and trials. Individual trial variance is large enough that any single press tells you nothing reliable. After several trials, a pattern may emerge — or it may not, because laboratory binding conditions (isolated press, pure 250ms tone onset) are harder to reproduce in a browser.
The structural gap the simulation can't close: the thing being measured is the process doing the measuring. Your report is the only instrument — and the instrument was changed by what it's reporting on.