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← Revision 61 as of 2022-08-22 14:16:10 ⇥
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| = Epoching and averaging = This tutorial fills the gap between the previous tutorial (review and clean continuous recordings), and the introduction tutorials (source analysis of evoked responses). It explains how to epoch the recordings, do some more pre-processing on the single trials, and then calculate their average. <<TableOfContents(2,2)>> == Import in database == The raw file viewer provides a rapid access to the recordings, but most of operations cannot be performed directly on the continuous files: most of the pre-processing functions, averaging, time-frequency analysis and statistical tests can only be applied on blocks of data that are saved in the database (ie. "imported"). After reviewing the recordings and editing the event markers, you have to "import" the recordings in the database to go with further analysis. * In the Event tab: select the menu Import > Import > Import in database (only when the file viewer is open), * In the database tree: Right-click on the nodes "Link to raw file" > Import in database. Now, right-click on the file with power line correction:''' Raw | sin(60Hz 120Hz 180Hz) > Import in dabase''' {{attachment:importMenu.gif}} You would get the same menu from the event tab, when the file viewer is open: menu Import > Import in database. __Warning__: If you right-click on the subject node > Import EEG/MEG, and select the tutorial .ds dataset, you would be able to import blocks of the continuous file in the database, but you would not have access to the modified events list or the SSP operators. Therefore, you would not import data cleaned for the ocular and cardiac artifacts. The modified events list and the signal space projectors are saved only in the "Link to raw file" in the Brainstorm database, not in the initial continuous file. {{attachment:importOptions.gif}} Set the import options as they are represented in this figure: * '''Time window''': Time range of interest. Now we want to keep the whole time definition, we are interested by all the stimulations, so leave the default values * '''Split''': Useful to import continuous recordings without events, to import successive chunks of the same duration. We do not need this here. * '''Events selection''': Check the "Use events" option, and select both "left" and "right". The value between parenthesis represents the number of occurrences of this event in the selected time window (would change if you modify the time definition on top of the figure) * '''Epoch time''': Time segment that is extracted around each marker, to create the epochs that are saved in the database. Set it to [-100, +300] ms * '''Use Signal Space Projections''': Use the active SSP projectors calculated during the previous pre-processing steps. Keep this option selected. * '''Remove DC Offset''': Check this option, and select: Time range: [-100, 0] ms. For each epoch, this will: compute the average of each channel over the baseline (pre-stimulus interval: -100ms to 0ms), and subtract it from the channel at all the times in [-100,+300]ms. * '''Resample recordings''': Keep this unchecked * '''Create new conditions for epochs''': If selected, a new condition is created for each event type (here, it will create a condition "Event_5"). If not selected, all the epochs from all the selected events are saved in the same condition, the one that was selected in the database explorer (if no condition selected, create a condition called "New condition"). * Click on Import and wait. {{attachment:importShortEpoch.gif}} {{attachment:importDb.gif}} |
Differences between revisions 5 and 61 (spanning 56 versions)