Hi Arno,<div><br></div><div>If you can keep the S/N and the impedances same for each electrode this might not be the case. I did the following experiment: I used 64 channel activeBPoducts electrodes. Then used LORETA, as well as ICA based dipfit in eeglab. I did not calculate the dipole localization errors (I do not know how to do that without knowing where the actual sources should be). I found a set of sources. Then I used the SAME set of electrodes but took out half of them, and only used 32 electrodes which were distributed like 10-20 system. Of course sources have changed. What I want to tell you is that smaller number of electrodes might reduce the localization accuracy (?), but there is another factor: WHEN I coincidentally chose electrodes which are the noisy ones, it looked as if localization problems increased. I played with the subset of selected electrodes, and noisier electrodes had more impact. For instance LORETA is very sensitive to noise. You can use this method to test all different localization approaches (which may have different relationship with the electrode-number/source-accuracy ratio).</div>
<div><br></div><div>I do not know which system(s) you actually used in the past, but I used easy cap-ant (24ch) in my PhD, neuroscan (32 ch), biosemi (64ch) and activeBP electrode and cap (64ch) in the past and now I am using egi (128ch) in my postdoc trainings. I do not want to favor any company here nor do I wish to make a company look bad. I do not have any interest in this. Of course the logic 'more is better' bring a lot of problems: you have to localize those electrodes in a better way (then, buy a localizer ! aha!), then put gel into lots of electrodes (be patient then ! aha!) or maybe use egi, just dip the cap in a solution (pay more money! aha!) Anyways, there tons of people out there publishing source localization papers with 32 channels and it is a pity that your paper is not getting published (snd it to another journal then! aha!).</div>
<div><br></div><div><br></div><div>Thanks:)</div><div>Baris</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Nov 8, 2012 at 9:16 PM, Arnaud Delorme <span dir="ltr"><<a href="mailto:arno@ucsd.edu" target="_blank">arno@ucsd.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">I disagree with Baris and Patrick. 128-channels is better than 64 in many ways. I had done some testing on source localization (comparing dipole localization error from 256 (ground truth) down to 19 electrodes) and below 72 channels, the error starts to increase (not published unfortunately). <div>
<br></div><div>Only record with 64 channels if you do not have the choice. If you are planning to scan electrode positions, use 128. If you are planning to coregister with the subject's MRI, definitely use 128.</div><div>
<br></div><div>In choosing between Biosemi and Brainproduct, Biosemi systems are less expensive than Brainproduct. However, with Biosemi, you cannot check electrode impedances. If you have the funds, you might want to get the Brainproduct system. If your funds are limited, you might want to get Biosemi. And remember there is also Neuroscan, EGI, Ant and Guger Technologies who all offer decent products as well.</div>
<div><br></div><div>Best,</div><div><br></div><div>Arno</div><div><div class="h5"><div><br><div><div>On 8 Nov 2012, at 05:02, Patrick Simen wrote:</div><br><blockquote type="cite">
<div style="word-wrap:break-word">I only have experience with ActiCHamp, so it may be true that BioSemi is better. <div><br></div><div>However, I just wanted to say that I haven't found it at all difficult to reduce impedance with the BrainProducts system. It also didn't feel uncomfortable to me when I wore the cap several times and had the electrodes inserted by students (nor when I inserted them myself -- it was easy enough that I could prep myself completely and quickly without assistance from anybody else -- I just needed a handheld mirror to see the occipital electrodes). </div>
<div><br></div><div>The only thing I really noticed was that reducing impedance was far (!!) easier and more comfortable than the usual process with passive-electrode caps in my previous lab. But that would probably be true with any active electrode cap, I guess.</div>
<div><br></div><div>Incidentally, an engineer at Brain Products also told me something that agrees with what Baris says below: there's not much point in going beyond 64 electrodes. </div><div><br></div><div>Best,</div>
<div><br></div><div>Pat.</div><div><br></div><div><div>On Nov 7, 2012, at 11:10 PM, Baris Demiral wrote:</div><br><blockquote type="cite">Yes I have experience with both. Use BioSemi. Here is my reasoning:<div><br></div><div>
I used full BioSemi Active2 system (cap+amplifier+LabView+response bix etc.) Electrodes are easy to insert, small, easy to reduce impedance, comfortable. You put the gel before the electrodes are placed.</div>
<div><br></div><div>I used BProduct Active electrodes with Neuroscan amplifier+electrode box. Electrodes are very large, not easy to place the elctrodes on the cap, subjects feel discomfort. In order to reduce this effect you may need to place the electordes on the manican before you put it on the subject which is weird. Since you will have 128 electrodes !! Also, you ned to insert the gel after you put the electrodes through a small opening, which makes impedance reduction relatively hard to obtain.</div>
<div>Kinking problem is likely to occur due to the difficulty of placing the electrodes.</div><div><br></div><div>Buy BioSemi. even 64 channel is fine for many applications and source localization. 128 too much and not very necessary (read some papers related to source localization, you will notice that after 60 channels quality does not change much). Kinking proble is likely to occur due to the orientation of the cable placed initially in the beginning. </div>
<div><br></div><div>Feel free to call me if you need further help. But, I would suggest (if you are going to pay a lot of money in this business) go and observe the systems in the labs live.</div><div>Baris</div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Fri, Nov 2, 2012 at 11:42 AM, Jason M Cowell <span dir="ltr"><<a href="mailto:cowell@uchicago.edu" target="_blank">cowell@uchicago.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-US" link="blue" vlink="purple">
<div><p class="MsoNormal">Hello,<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Our lab is presently in the process of acquiring several active 128- electrode systems. Does anyone have experience with both the Brain Products actiCHamp and the BioSemi ActiveTwo? We are comparing both and are interested in the quality
of these data, particularly in noise issues. Are either of the systems more compatible with EEGLAB? Any help or experience, particularly using the actiCHamp would be greatly appreciated.<u></u><u></u></p><p class="MsoNormal">
<u></u> <u></u></p><p class="MsoNormal">Jason<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Jason M Cowell, Ph.D.<u></u><u></u></p><p class="MsoNormal">Postdoctoral Scholar<u></u><u></u></p>
<p class="MsoNormal">Social Cognitive Neuroscience Lab<u></u><u></u></p><p class="MsoNormal">University of Chicago<u></u><u></u></p><p class="MsoNormal">5848 S. University Ave.<u></u><u></u></p><p class="MsoNormal">Chicago, IL 60637<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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