Extract epochs and set their baseline

Epoch extraction uses the selected tag in the recording’s .t timing file. Prepare event selection, condition recoding and subdivision in MARKER first. The log reports input event counts and the final extracted count per condition.

Epoch coordinates

Pretrigger and posttrigger define the samples on either side of the event, including the trigger sample itself: the total is pretrigger + 1 + posttrigger. At 256 Hz, 128 pretrigger and 77 posttrigger samples give 206 samples, from −500 ms to approximately +301 ms. The trigger is zero-based index 128, or one-based point 129.

Check whether a control uses points/samples or milliseconds. Do not copy a point index into a millisecond field. The epoch baseline is a processing setting; changing a viewer’s baseline later does not regenerate stored epochs.

Extraction aligns to event onset. Timing interval duration has a separate role when a trial-selection profile uses a minimum event duration.

Outputs and checks

Extraction writes <filtered>.SES and <filtered>.SES.CON; the latter associates extracted trials with conditions. The timing file remains the source event definition. Keep the matching sensor configuration with the epoch data.

If events near recording boundaries cannot supply the requested samples, check the final counts and diagnostics. A missing timing tag, incompatible channel configuration or unreadable prerequisite must be resolved before continuing.

Longer epochs require new artefact assessment. To explore an alternative epoch window while preserving an established analysis, create a branch at epoch extraction. Reuse the compatible continuous preparation and ICA, then recalculate epochs and all affected later steps. Selecting only a later range never authorizes reusing incompatible earlier settings.