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

[Dwight Peterson]

Dr. Massimiliano,

         It is my understanding that many of the papers published on the
CDA average across the electrode pairs (or multiple pairs) prior to
generating the difference waveform that is the CDA (contralateral activity
minus ipsilateral activity).  So, for example, if you have activity
recorded from sites P3 and P4, for each trial type (RVF or LVF trials) you
have contralateral activity (e.g., RVF trials P3 activity and LVF trials P4
activity) as well as ipsilateral activity (e.g., RVF trials P4 activity and
LVF trials P3 activity). So, what you can do is take the average
contralateral activity at, for example P3 and P4, and the average
ipsilateral activity at P3 and P4, and then subtract the average
ipsilateral activity at P3/P4 from the average contralateral activity at
P3/P4.
        I've also been working with the CDA and found mediocre waveforms
when I collapse/average across both correct and incorrect trials.  My next
step is to analyze my data using only correct trials (which is problematic
because I lose a number of my trials at larger set sizes). There is
justification to analyze only correct trials, however, as seen in previous
literature.  For example, Luria et al. (2009) in a paper regarding the CDA,
published in JOCN, use the average technique I mentioned above, and also
only included correct trials.
        Do your bins simply include all the EEG datasets that you processed
already for, say LVF/RVF and condition type?   If so you could modify these
datasets to only include correct trials and then update the datasets in
each of your bins.


        Please let me know how this works out for you.

Regards,


--Dwight--

On Mon, Nov 5, 2012 at 8:58 AM, Massimiliano Papera <
massimiliano.papera at googlemail.com> wrote:

> 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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-- 
Dwight J. Peterson, M.A.
Graduate Assistant
Cognitive and Brain Sciences
Department of Psychology/296
Memory and Brain Laboratory
University of Nevada, Reno
Reno, NV 89557
Cellular: 319-231-8596
Laboratory: 775-682-8667
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