[Eeglablist] Scroll Plot Marked Trial / Channel Identification

[Matt Craddock]

On 28/11/2012 16:41, Frank Preston wrote:
> Hi,
>
> If Scroll Plot is opened after trials have been marked by EEGLab, the
> channel which caused the trial to be marked is highlighted in red. We
> would like to know which channel is marked and it is often very
> difficult to tell because the plotted signal is outside of range by
> quite a bit. Is there an easy way to tell this, perhaps by highlighting
> the channel on the y-axis?
>
> We are viewing results from a BioSemi Active 2 system. We record 72
> electrodes, 66 of which are on the cap.
>
> Thank you,
>
>    .. Frank

Hi Frank,

When you say the signal is often outside of range, I'm guessing this 
must be true of quite a few channels, since otherwise which one is 
missing would be obvious. My best guess why that would be would be 
because of Biosemi recording data with the DC offset. did you baseline 
correct after epoching, remove the mean of the channel, or high-pass 
filter the data at any point?  If not, any of those should lessen your 
problems. Rather than take any of those steps right now , simply try 
selecting "Remove DC offset" while displaying the scroll plot - afaik 
that removes the DC for each epoch for each channel (or over the 
displayed time window for continuous data) - only for display - so 
should bring a channel that's out of range back somewhere displayable 
(or at least enough of it to be able to see which chan it is). This 
works fine for bringing raw Biosemi back into the display range, in my 
experience.

Course, I might be making the wrong guesses, in which case just do what 
Tarik says. :)

Cheers,
Matt

-- 
Dr. Matt Craddock

Post-doctoral researcher,
Institute of Psychology,
University of Leipzig,
Seeburgstr. 14-20,
04103 Leipzig, Germany
Phone: +49 341 973 95 44