Preprocessing

Open new dataset

We open a new dataset. This is an n-back task with 3 levels of difficulty: 0-back, 1-back, 2-back and 3-back, so there are 3 different markers and 7 repetitions of each. The task was almost 40 minutes in total.

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Also load marker file:

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NOTE: the oxy file that is automatically created from the COBI Studio recording was scaled to the baseline consisting of 100 samples at the beginning of the recording. Therefore, there is limited use of that file!

You see a lot of markers here, so as described above, we go right-click → toggle marker visibility and the markers are then removed from your view.

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This opens the 2x8 layout view:

There are no saturations in these data, the signal looks fine.

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Exclude bad data

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Top left: bad optode contact; there is hair trapped under the optode. You can try to resolve this by placing a headband over the optode to keep it closer to the skin or make the strap tighter. Optode 1 and also a little bit 5 and 3 in this example shows the effect of hair. The sharp change towards the end of the x-axis shows an adjustment where the hair was moved out of the way.

Makeup needs to be removed because it reflects a lot of light and will distort the signal.

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Top right: Saturated signals mean the signal is larger than the machine can handle and this signal cannot be recovered. We want a maximum of 3,500 mV. Therefore, we need to make sure we prevent this issue. This can be done prior to the experiment by reducing the gain or the light intensity. If this issue remains undetected until after the experiment, the optode where there is saturation will need to be eliminated from the analysis. 

Lower left: spike from motion artifact. Can either eliminate (preferred) or correct for it. Try to prevent by tightening the strap without tension but less possibility to move.

 Lower right: good signal.

Filtering

Now go to the bottom tool bar and click the tab “Refine”

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Click “Calculate oxygenation”.

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Oxygenation data

HbO: oxygenated hemoglobin (red by default)

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Time: you can select the time window to be displayed as needed, i.e. the range of the x-axis.

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Processing

Creating blocks

In the bottom pane of the main data window, click “Define Blocks”.

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If you click “Manage” on the bottom, you see this screen, which shows you all the markers with their block number, onset and offset times, and their duration. You can sort or delete them here.

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Automated block creation

Instead of adding all blocks one by one, we can add all at once with previously configured presets. On the bottom pane, click “Automation”:

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You can then go back to view and edit your blocks by right-click → Manage → Manage Blocks

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Saving data

Next, we save the file to the data space: click “Save” in bottom pane.

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Target location is Data Space:

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Data by the block

A window with a text view of your data will open. This list contains all HBO, HBR and OXY data by block and time.

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Different views

If you double-click on a block, you see the data for that block. On the bottom, under Graph Type, you can change the display.

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You can open multiple blocks at the same time to look at them together.

Change baseline

Note that these data have been calculated using the global baseline. We now want to change that. We want to look at the data for the blocks without the influence of the time before the blocks started.

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If you now go back to the Data Space tab, you see a lot of new variables created and they all say “Baseline corrected”. Right-click → view.

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Graphs

This shows you all averages of HBO for each n-back block for each optode.

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On the bottom, you can change the graph type under and group type. Here 7 trials per block by group (o-back, 1-back, 2-back, 3-back):

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Instead of showing each trial separately, you can group the trials:

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Under Graph type → bar graph, you can see the average across the 7 trials of each block:

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We can now look at the results in different views:

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Graph type → Bar (2 by 8) provides this view in which we see each optode organized from left to right as the plate is arranged on the participant’s forehead:

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Temporal view

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