[Eeglablist] Baseline removal in dead channels

[Makoto Miyakoshi]

Dear Gorka,

If you recorded EEG with DC and if you checked your channel activity
with scroll plot, and if you see normal ERP after baseline correction
(actually it should be after high-pass), then my guess is that your
data have huge DC drifts.

run this code in matlab and tell me what you see. Right after
importing your data,

figure; plot(EEG.data)

Makoto

2012/10/23 Gorka Fraga Gonzalez <gorkafraga at gmail.com>:
> Dear EEGlab experts,
>
>
>
> I am analyzing data collected with a Biosemi 64 channels system.  After a
> large sample tested one electrode did not get any signal in the last
> subjects so it  was manually checked and apparently is dead.
>
>
> However after preprocessing  data without excluding this channel I found a
> normal ERP average. The data was analysed in EEglab as it follows:
>
>
>
>   Import ref average of mastoids//  bandpass filter (1-70)// downsample to
> 256hz// Epoched// Remove baseline (…)
>
>
>
> I found that it was only after the “remove baseline “step that I could see
> signal in that channel when manually scrolling the data.
>
>
>
> It would be great if any of you could give me an explanation on this, since
> after reading about what the “baseline removal” procedure does it is still
> not clear to me why this could happen
>
>
>
> Many thanks in advance
>
> Gorka
>
>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego