[Eeglablist] syncing time 0 ms to stimulus onset

[Tarik S Bel-Bahar]

Hello Julia, Some notes below that might help. cheers.



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Using Netstation is probably simplest here. One way might be to create new
"extra" events (e.g., your "true/correct 0 time event) within Netstation
before export to Netstation. This can be done manually, or automatically
via the segmentation waveform tool. These extra events should show up at
wherever you create them within each segments. You should be able to do add
these events within the continuous data or epoched data, both within NS. In
the segmentation tool, there should be an option to not create segments but
rather create new events based on the segmentation tool specs.Then these
should export into eeglab too.

Within eeglab, you can simply go the GUI, and add single events at the
correct locations. This is also scriptable if you examine the result of the
eegh command after successfully inserting an event via the eeglab gui.

Also possible with eeglab: Create new events as well that are at the
correct time in the segments/epochs. This may also involve modifying the
values of the times. Alternatively, you could export the continuous data
from netstation, and then also process/add/change events and segment/epoch
all within eeglab. Alternatively, also within eeglab, you could read a text
file with new events, and add these events to the correct place in each
segment. If you haven't had a chance to, to start, google past eeglablist
postings and review the online tutorial for info regarding adding events,
coding, scripting, etc...

Although it's unclear to me from your note, one possible problem you might
be having is that you want your segments/epochs to be generated so that
they each the same length (such as 2 or 3 seconds), or that they all have
the correct 0 time at the same location within the segment, or  both. I
think what you need is segments that are all the same length of time, and
where the time before or after 0 within each segment is variable.

I assume your issue is not about jitter of the stimulus onset, as that
should present no problem for 0 time locking.How eeglab is reading the
epochs you export from Netstation may also depend on exactly what "time"
(e.g., relative time) in the NS segmentation tool or file export tool
settings.
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On Wed, May 25, 2016 at 3:01 PM, julia campbell <julia.d.campbell at gmail.com>
wrote:

> Hello all,
>
> I am working with exporting .raw files from EGI Netstation to EEGLab.
> Before I export the Netstation files, I high-pass filter the continuous
> file and then ‘segment’ the data to create epochs.
> My stimuli have timing offsets that are programmed into the segmentation
> process in Netstation.
> As a result, when I examine the data in EEGLab, I have a stimulus marked
> as occurring before 0 ms latency.
> How can I mark 0 ms as the same point that the stimulus occurs?
>
> Thank you for your help!
>
> *Julia Campbell, Ph.D, Au.D, CCC-A, F-AAA*
> *Assistant Professor*
> *Communication Sciences and Disorders*
> *The University of Texas at Austin*
>
>
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