>From my previous experience, and from the previous e-mail exchanges in this mailing list (as well as the algorithms proposed in some of the EEGLAB toolboxes, such as ADJUST) I see no problem of not including the EOGs in the ICA based artifact rejection. That being said, I only use EEG channels in ICA based correction, with their locations clearly defined, and I do not include EOGs for the very similar reasons you proposed.<br>
<br>The EEG channels will be good enough (or maybe I should say 'strong enough') to capture the eye movement sources. You can use EOG channels if you further want to examine some other aspects of the data if needed. Maybe, for instance, calculating the absolute value of the differences between the horizontal electrodes, and the value of the vertical EOG during the epoch to determine wheher there were significantly more or less eye movement-induced potentials between the conditions. In some paradigms people may move/blink their eyes more often in one condition than the other condition. But at the end, artifact correction should not bias the data towards one condition under such circumstances.<br>
<br>Best,<br>Baris<br><br><div class="gmail_quote">On Tue, Jun 7, 2011 at 10:14 PM, Chang Gu <span dir="ltr"><<a href="http://chang.gu">chang.gu</a>@<a href="http://vanderbilt.edu">vanderbilt.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear colleagues,<br><br>I'm using ICA to clean the data, but I'm wondering that if we could remove the eye channels before conducting ICA. <br>
<br>We're using 128-channel EGI recording system and there're 8 eye-channels on the face picking up eye signals like blink and movement. <br>
(1). For these 8 channels, they're usually recording huge potentials comparing with regular channels on the sculpt: the signal amplitude from eye channels could be 100 times to channels close to vertex before average re-reference.<i> If I run ICA on all channels, is it possible that the big variability in the eye channels influence the decomposition result?</i> From our data, it seems that signals from eye channels draw most of the attention of ICA and ICA decomposes many components of eye artifacts. However, we're interested in decomposing brain-signal rather than eye-signals. Also, is it possible that data-scale differences from eye channels (around 100 micro volts) and regular channels (less than 3 micro) may influence the performance of ICA algorithm? <br>
<br>(2). Since the eye-channels are on face, very often they have poor contact with skin and dry out easily. From the ICA 2D topographic results, we often found maps with a single red/blue dot on eye channel, suggesting the distinct temporal character of the signal from this channel.<i> I'm wondering that if this 'bad' channel may affect the overall ICA deposition. </i><br>
<br>We tried removing these 8 eye-channels: other channels nearby also record eye potentials (but not as strong as eye-channels for sure) and ICA are able to separate eye-components from the EEG signal...<br>I'm wondering that, is there any theoretical concerns about removing eye-channels? <br>
<br>Thanks in advance!<br><br>Chang <br clear="all"><font color="#888888"><br>-- <br>Chang Gu<div>Psychology & Human Development</div><div>Vanderbilt University </div><div>Nashville, TN</div><div><br></div><br>
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