[Mne_analysis] Baseline calculation

[Vancelette, Reid Vincent]

Hi Steven and everyone else,

We used auditory presentation for our study. This means that the latencies vary depending on the word and the sentence. We unfortunately didn’t normalize all of the lengths of all the segments so that the matched. Is there any way to go around this problem? I know the lengths of each of the segments in all of the sentences: this is how we initially created the triggers for our experiment.

-Reid

From: Stephen Politzer-Ahles [mailto:politzerahless at gmail.com]
Sent: Friday, March 30, 2012 5:19 AM
To: Vancelette, Reid Vincent
Cc: mne_analysis at nmr.mgh.harvard.edu
Subject: Re: [Mne_analysis] Baseline calculation

Hi Vancelette,

Is the time between the beginning of a sentence and a given trigger always the same across items? (That should be the case if the number of words is always the same and you used serial visual presentation; if the position of a given trigger varies across items and/or you used auditory presentation, though, then the latencies probably vary.) If this latency is always the same then you can just add that latency to what the baseline interval would be for each trigger. For instance, if the baseline for the first trigger were -100 to 0, and the second trigger always appeared 800 ms after the first, then the baseline for the second could be -900 to -800.

Best,
Steve
On Thu, Mar 29, 2012 at 10:42 AM, Vancelette, Reid Vincent <RVANCELETTE at partners.org<mailto:RVANCELETTE at partners.org>> wrote:
Hi all,

I am currently in the process of performing preprocessing on my MEG/EEG data and am trying to correctly calculate a baseline. I am working with whole sentences that have several triggers within each sentence to mark particular areas of interest (for example: the noun, the verb). The current way that we calculate the baseline is from 100 ms before each of the triggers. Is there any way that I can calculate the baseline from the first trigger of each of the sentences (which happens to correspond to the beginning of the sentence) and apply that to each of the triggers within that particular sentence instead of having to calculate it 100 ms before each of the triggers? I am asking this because as of right now we are basically forced to calculate the baseline while the subject is hearing the sentences, which can bias the data.

Thanks in advance,

Reid

Reid Vancelette
Research Assistant to
Dr. David Caplan M.D., Ph.D.

Massachusetts General Hospital
Neuropsychology Lab
175 Cambridge Street, Suite 340
Boston, MA 02114

Phone: (617) 724-8846<tel:%28617%29%20724-8846>
Email: rvancelette at partners.org<mailto:rvancelette at partners.org>



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--
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://www.linguistics.ku.edu/
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