Dr. Massimiliano,<div><br></div><div> 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. </div>
<div> 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. </div>
<div> 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. </div>
<div><br></div><div><br></div><div> Please let me know how this works out for you.</div><div><br></div><div>Regards,</div><div><br></div><div><br></div><div>--Dwight--</div><div><br><div class="gmail_quote">On Mon, Nov 5, 2012 at 8:58 AM, Massimiliano Papera <span dir="ltr"><<a href="mailto:massimiliano.papera@googlemail.com" target="_blank">massimiliano.papera@googlemail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p class="MsoNormal">Dear All,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">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.</p>
<p class="MsoNormal">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.</p>
<p class="MsoNormal">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.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thank you</p>
<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt;line-height:normal;text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New"">ERP = pop_binoperator( ERP, {</span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'LH = [18 23
24]'</span><span style="font-size:10.0pt;font-family:"Courier New"">
</span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'RH
= [14 28 27]'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb1= b1@RH-b1@LH label CDA LVF20'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb2= b2@LH-b2@RH label CDA
RVF20'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb3= b3@RH-b3@LH label CDA LVF40'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb4= b4@LH-b4@RH label CDA
RVF40'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb5= b5@RH-b5@LH label CDA LVF22'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nb6= b6@LH-b6@RH label CDA
RVF22'</span><span style="font-size:10.0pt;font-family:"Courier New"">});</span><span style="font-size:12.0pt;font-family:"Courier New""></span></p>
<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt;line-height:normal;text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""><span>
</span></span><span style="font-size:12.0pt;font-family:"Courier New""></span></p>
<p class="MsoNormal">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).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">To get the CDA I now subtract <span> </span>the activity between left and right visual
field trials for all of the 3 conditions:</p>
<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt;line-height:normal;text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New"">ERP = pop_binoperator( ERP, {</span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nbin1= b1-b2
label CDA 2T0D'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nbin2=b3-b4 label CDA 4T0D'</span><span style="font-size:10.0pt;font-family:"Courier New""> </span><span style="font-size:10.0pt;font-family:"Courier New";color:#a020f0">'nbin3=b5-b6 label CDA 2T2D'</span><span style="font-size:10.0pt;font-family:"Courier New""> }); </span><span style="font-size:12.0pt;font-family:"Courier New""></span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">This gives me 3 CDA component, one for each condition.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Does anyone know if this is correct to compute the CDA?</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thank you </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thanks to everyone</p><span class="HOEnZb"><font color="#888888"><p class="MsoNormal">Massimiliano Papera<br></p>
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-- <br>Dwight J. Peterson, M.A.<br>Graduate Assistant<br>Cognitive and Brain Sciences<br>Department of Psychology/296<div>Memory and Brain Laboratory<br>University of Nevada, Reno<br>Reno, NV 89557<br>Cellular: 319-231-8596</div>
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