[Eeglablist] Performining the t-test and highiliting the area

[cyril pernet]

Hi Vijay

Alex proposal is fine although that assumes that you are happy loosing 
information related to trial variance and also you are not bothered by 
multiple comparisons (doing that many t-test will automatically lead to 
some false positives)

as an alternative, you can do the statistical analysis with LIMO EEG 
(EEGlab toolbox to download) - that will allow you to model congruent 
and incongruent conditions per subjects and then test across subjects 
for a significant differences (in fact across all electrodes and time 
frames and using clustering to control the false positive rate).
--> there is a tutorial which show a case very similar .. it should be 
easy enough to do on your data

Cyril


Subject:
[Eeglablist] Performining the t-test and highiliting the area
From:
Vijay Narne <vijaynarne at gmail.com>
Date:
11/05/2012 05:54

To:
eeglablist at sccn.ucsd.edu


Dear List,
             I am Vijaya Kumar Narne, PhD. We are running the 
experiments on N400. We would like to compare ERP of the congruent and 
incongruent condition. We are intrested in running t-test and highliting 
the area of N400 in EEGLAB.  As we are new to EEGLAB, if any one help us 
do this.
Thanking you
Vijay


Subject:
Re: [Eeglablist] Performining the t-test and highiliting the area
From:
Alex Davila <axel.1963 at hotmail.com>
Date:
14/05/2012 20:26

To:
<vijaynarne at gmail.com>, <eeglablist at sccn.ucsd.edu>


Dear Vijaya,

I assume that your two conditions are run on the same participants 
(repeated measures). Then, what you need to do is just this:

1. Define the variable D = C - I

where C: your variable for the congruent condition and I: your variable 
for the incongruent condition.

2. Calculate the mean M and the sample standard deviation S for D.

3. Calculate t = M/(S/rootsquare(N))

where N: your number of participants.

4. Depending on your hypothesis, compare your calculated t with a one 
tail or two tail table t-student value. I'd suggest to use an alpha 
value identical to those available in the relevant literature.

5. As you're interested in the N400 value, I assume you may extract it 
from your ERP data of potentials across the time domain where you 
may identify local maxima and minima for each participant.

6. Of course, before getting this data, you need to apply the standard 
averaging procedure to extract the ERP signal from the noise.

All the best,

Alex.

-- 
Dr Cyril Pernet,

Academic Fellow
Brain Research Imaging Center
http://www.bric.ed.ac.uk/
Division of Clinical Neurosciences
University of Edinburgh
Western General Hospital
Crewe Road
Edinburgh
EH4 2XU
Scotland, UK

cyril.pernet at ed.ac.uk
tel: +44(0)1315373661
http://www.sbirc.ed.ac.uk/LCL/
http://www.sbirc.ed.ac.uk/cyril


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