[Eeglablist] How to compute the CDA in EEGLAB (contralateral delay activity)

[Gunseli, E.]

Dear Massimiliano,

Probably b1 includes the trials at which the memory item is presented on the left visual field and b2 is when it is presented on the right visual hemifield.
Then the CDA should be calculated with the below formula:
nbin1= ((b2 at LH + b1 at RH)/2 - (b1 at LH + b2 at RH)/2 ) label CDA

I would be glad if some expert member would confirm the formula.

By the way, including only the trials with correct behavioral response would be a better idea.

Best regards,
Eren Gunseli

From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Massimiliano Papera
Sent: Monday, November 05, 2012 17:59
To: eeglablist at sccn.ucsd.edu
Subject: [Eeglablist] How to compute the CDA in EEGLAB (contralateral delay activity)

Dear All,

I am investigating the relationship between Attention and Memory and would like to use the Contralateral Delay Activity (CDA) as a correlate of the visual working memory. I am dealing with the bin operations function.
I would like to check through the Discussion list if anyone who is familiar with the CDA knows I am using the right coding to get my CDA component across three different conditions.
I am investigating 3 different pair of electrodes (p3-4, o1-2 and p7-8) for correct and incorrect responses. However I am not sure if I need to filter out the incorrect trials.

Thank you
ERP = pop_binoperator( ERP, {'LH = [18 23 24]' 'RH = [14 28 27]' 'nb1= b1 at RH-b1@LH label CDA LVF20' 'nb2= b2 at LH-b2@RH label CDA RVF20' 'nb3= b3 at RH-b3@LH label CDA LVF40' 'nb4= b4 at LH-b4@RH label CDA RVF40' 'nb5= b5 at RH-b5@LH label CDA LVF22' 'nb6= b6 at LH-b6@RH label CDA RVF22'});

This gives me 6 bins, 2 per each of the 3 conditions. Each pair gives me erp for either left visual field (LVF) or right visual field (RVF).

To get the CDA I now subtract  the activity between left and right visual field trials for all of the 3 conditions:
ERP = pop_binoperator( ERP, {'nbin1= b1-b2 label CDA 2T0D' 'nbin2=b3-b4 label CDA 4T0D' 'nbin3=b5-b6 label CDA 2T2D' });

This gives me 3 CDA component, one for each condition.

Does anyone know if this is correct to compute the CDA?

Thank you

Thanks to everyone
Massimiliano Papera
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