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Calculation of epoch statistics

The calculation of statistical signal parameters for each trial forms the basis of artefact detection in EMEGS. This calculation is configured on the next dialog, shown here below.  By default, all points of the epoch are included in these calculations, but calculations may be restricted to a subset of points. Parameters must be calculated on the raw data ("calc without average reference") , but in addition  - if an average reference transformation is activated - they can be calculated after application of an average reference ("calculate parameters with average reference"), which gives better editing results for high density EEG configurations.

As the application of an average reference is heavily distorted by generally artefactual channels and trials, the parameter calculation with an average reference applied requires two additional routines that scan the data for such generally artefactual channels ("exlude outlier channels") and trials ("exclude outlier trials").

After the calculation of the epoch statistics, these can be inspected by selecting the parameter mode on the bottom right corner of the ERP display. The parameters are displayed as histograms of trials for each channel:

Depending on wether you have selected to calculate parameters also after application of an average reference, a different number of new files have appeared in your data folder. Without average reference, only one additonal *.AEM-file has appeared, containing the statistical paramters for all channels and trials:

The exclusion of outlier channels required for an average reference creates two additional files, so called electrode status files (*.*est), containing the good/bad-status of all sensors. The exclusion of outlier trials creates the *.AEM.AWE file, which contains the good/bad status for all trials for all channels. The following second pass through the parameter calculation routine (now with a mostly undistorted  average reference) produces the file *.AEM.AR, which is equal to the *.AEM file, except that it contains the statisical parameters after application of the average reference. Your folder in this case looks like this: