[Eeglablist] Baseline removal in dead channels

[Gorka Fraga Gonzalez]

Hi Steve,

Thanks for your replay.

I meant the average in that dead channel. When scrolling data before
baseline correction I was not able to display the signal in that channel
unless using a very large scale (above 2000) when of course all lines were
flat . However after baseline correction it displayed signal similar to the
rest of the channels. This channel also showed a flat line in the Biosemi
actiview software when recording.

greets
Gorka


On 24 October 2012 04:28, Stephen Politzer-Ahles
<politzerahless at gmail.com>wrote:

> Hi Gorka,
>
> Do you mean you found a normal ERP average in other channels? That would
> not be surprising, because baseline-correcting one channel doesn't affect
> other channels. On the other hand, if you mean that the channel had no data
> before baseline correction but then suddenly had a normal ERP after
> baseline correction, then I'm not sure why that would happen either...
>
> Best,
> Steve Politzer-Ahles
>
> On Tue, Oct 23, 2012 at 9:47 AM, Gorka Fraga Gonzalez <
> gorkafraga at gmail.com> wrote:
>
>> 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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>
>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/
>
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