calibration

Calibration is the short training session at the very start of a BCI session, where the user produces known signals on cue. The system prompts: "now imagine moving your right hand," then "now your left," recording the brain activity each time. Because it knows what the user was told to do, it ends up with a small, labelled collection of examples — exactly what the decoder needs to learn from.

It is needed because no two brains are alike, and even the same brain differs from day to day. Electrode positions shift slightly, the person is more or less alert, the gel has dried a little — so a decoder tuned last week may not fit today. Calibration re-fits the decoder to this person, on this day, in this setup, which is why so many BCIs begin with a few minutes of these cued trials.

The trade-off is time and patience: long calibrations are tiring and eat into useful work. A major thread of research aims to shrink or skip them, by reusing models across sessions or letting the decoder keep adapting quietly while the system is actually in use.