Tutorial 5: Review continuous recordings

Authors: Francois Tadel, Elizabeth Bock, John C Mosher, Sylvain Baillet

Open the recordings

Let's look at the first file in the list: AEF#01.
Right-click on the Link to raw file. Below the first to menus, you have the list of channel types:

Select > MEG > Display time series (or double-click on the file).

It will open a new figure and enable many controls in the Brainstorm window.

The files we have imported here are shown the way they have been saved by the CTF MEG system: as contiguous epochs of 1 second each. These epochs are not related with the stimulus triggers or the subject's responses, they are just a way of saving the files. We will first explore the recordings in this epoched mode before switching to the continuous mode.

From the time series figure

From the time panel

From the page settings

Time selection

Epoched vs. continuous

Display mode: Butterfly/Column

Montage selection

Channel selection

If you click on the white or grey areas of the figure, it changes the current time.
If you click on the lines representing the recorded signals instead, it selects the corresponding channels.

Amplitude scale

A variety of display options allows you to adjust the amplitude scale for the recordings (vertical axis).

Additionally, you can zoom vertically to look at specific channels, without having to change the montage. Use the zoom/scrolll buttons on the right of the figure, or your mouse (CTRL+Mouse wheel to zoom, middle-click+move to scroll).


Time and amplitude resolution

In the Brainstorm interface, the axis resolution is usually set implicitly: you can set the size of the window, the duration or recordings reviewed at once and the maximum amplitude to show in the figure. These parameters are convenient to explore the recordings interactively but don't allow us to have reproducible displays with constant time and amplitude resolutions.

However, some applications are very sensitive to the horizontal and vertical scaling, such as the visual detection of epileptic spikes. The shapes of traces the epileptologists try to identify are altered by the axes resolution. This is detailed in the tutorial EEG and Epilepsy.

For this reason, we also added a menu to set the figure resolution explicitly. The distance unit on a screen is the pixel, we can set precisely how much time is represented by one pixel horizontally and how much amplitude is represented by one pixel vertically.
Right-click on the figure > Figure > Set axes resolution.

Note that this interface does not store the input values, it just modifies the other parameters (figure size, time window, max amplitude) to fit the resolution objectives. If you modify these parameters after setting the resolution (resize the figure, leave the button [AS] selected and scroll in time, etc) the resolution is lost, you have to set it again manually.

Filters for visualization

With the Filter tab, you can apply a band-pass filter to the recordings, or remove a set of specific frequencies (example: the 50Hz or 60Hz power lines contamination and their harmonics). The filters are applied only to the time window that is currently loaded. If the segment is too short for the required filters, the results might be inaccurate.

The option "Mirror signal before filtering" replicates the signal with a mirror symmetry on each side, to minimize the amplitude of the edge effects that these filters can generate. Otherwise the signal is padded with zeros on each side before filtering. These visualization filters are not very accurate, they just provide a quick estimate for visualization only, the results are not saved anywhere. To filter properly the continuous files, please use the Process1 tab (see tutorial #10).
The option "Filter full source files" is not useful for now, it will be described later.

After testing the high-pass, low-pass and notch filters, uncheck them. If not you may forget about them, and they will stay on until you restart Brainstorm. Note that as long as there are visualization filters applied, the title of the Filter tab remains red.

Mouse and keyboard shortcuts

Keyboard shortcuts

Mouse shortcuts

Feedback: Comments, bug reports, suggestions, questions
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Tutorials/ReviewRaw (last edited 2017-07-19 13:05:28 by FrancoisTadel)