<span class="Apple-style-span" style="font-family:arial,sans-serif;line-height:16px"><div class="gs_r" style="margin-top:1em;margin-right:0em;margin-bottom:1em;margin-left:0em"><h3 class="gs_rt" style="width:44.5em;font-weight:normal;margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">
<a href="http://www.sciencedirect.com/science/article/pii/S1388245799000449" style="color:rgb(0,0,204)"><font class="Apple-style-span" size="1">The polar <b>average reference </b>effect: a bias in estimating the head surface integral in EEG recording</font></a></h3>
<div class="gs_ggs gs_fl" style="white-space:nowrap"><a href="http://kops.ub.uni-konstanz.de/bitstream/handle/urn:nbn:de:bsz:352-opus-19025/Junghoefer_et_al_1999_PARE.pdf.pdf?sequence=1" style="color:rgb(119,119,204)"><font class="Apple-style-span" size="1"><span class="gs_ctg2" style="font-weight:bold">[PDF]</span> from uni-konstanz.de</font></a></div>
<div class="gs_a" style="color:rgb(0,128,0)"><font class="Apple-style-span" size="1">M Junghöfer, T Elbert, DM Tucker… - Clinical Neurophysiology, 1999 - Elsevier</font></div><div class="gs_rs"><font class="Apple-style-span" size="1"><b>...</b> that the voltage time series reflects the difference in electrical potential between two <b>electrodes</b>. <b>...</b><br>
spatial derivative, such that current density measures with 19- or <b>32</b>-channel recordings <b>...</b> The<br>question for practical EEG recording is whether an <b>average</b> <b>reference</b> fulfils the criterion <b>...</b></font></div>
<div class="gs_fl"><font class="Apple-style-span" size="1"><a href="http://scholar.google.com/scholar?cites=17137298841162271237&as_sdt=2005&sciodt=0,5&hl=en" style="color:rgb(119,119,204)">Cited by 118</a> - <a href="http://scholar.google.com/scholar?q=related:BcowrX_q0-0J:scholar.google.com/&hl=en&as_sdt=0,5" style="color:rgb(119,119,204)">Related articles</a> - <a href="http://www.worldcat.org/oclc/315430049" style="color:rgb(119,119,204)">Library Search</a> - <a href="http://scholar.google.com/scholar?cluster=17137298841162271237&hl=en&as_sdt=0,5" style="color:rgb(119,119,204)">All 12 versions</a></font></div>
</div><div class="gs_r" style="margin-top:1em;margin-right:0em;margin-bottom:1em;margin-left:0em"><h3 class="gs_rt" style="width:44.5em;font-weight:normal;margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">
<a href="http://www.springerlink.com/index/R086736518RG8172.pdf" style="color:rgb(0,0,204)"><font class="Apple-style-span" size="1">Spatial sampling and filtering of EEG with spline laplacians to estimate cortical potentials</font></a></h3>
<div class="gs_ggs gs_fl" style="white-space:nowrap"><a href="http://www.tu-ilmenau.de/fakia/fileadmin/template/startIA/bmti_neu/div/HS/neues_layout/bmt/srinivasan_BT_1996_EEG_spatial_sampling.pdf" style="color:rgb(119,119,204)"><font class="Apple-style-span" size="1"><span class="gs_ctg2" style="font-weight:bold">[PDF]</span> from tu-ilmenau.de</font></a></div>
<div class="gs_a" style="color:rgb(0,128,0)"><font class="Apple-style-span" size="1">R Srinivasan, PL Nunez, DM Tucker… - Brain Topography, 1996 - Springer</font></div><div class="gs_rs"><font class="Apple-style-span" size="1"><b>...</b> Mapping the potential field is the most typical approach in studies of EEG topogra- phy, typically<br>
recorded with less than <b>32</b> <b>electrodes</b>, and often confounded by the assumption that a <b>...</b> The potential<br>field can be mapped with respect to the <b>average</b> <b>reference</b> (Bertrand et al. <b>...</b></font></div>
<div class="gs_fl"><font class="Apple-style-span" size="1"><a href="http://scholar.google.com/scholar?cites=7605044994983867216&as_sdt=2005&sciodt=0,5&hl=en" style="color:rgb(119,119,204)">Cited by 122</a> - <a href="http://scholar.google.com/scholar?q=related:UDPgMiGMimkJ:scholar.google.com/&hl=en&as_sdt=0,5" style="color:rgb(119,119,204)">Related articles</a> - <a href="http://direct.bl.uk/research/2A/19/RN010705691.html?source=googlescholar" style="color:rgb(119,119,204)">BL Direct</a> - <a href="http://scholar.google.com/scholar?cluster=7605044994983867216&hl=en&as_sdt=0,5" style="color:rgb(119,119,204)">All 7 versions</a></font></div>
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<br><br><div class="gmail_quote">On Tue, Jan 17, 2012 at 11:52 PM, Tarik S Bel-Bahar <span dir="ltr"><<a href="mailto:tarikbelbahar@gmail.com">tarikbelbahar@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>in my opinion, average reference is a good bet when you have denser coverage of the head with enough electrode density, something like 60 and above,</div><div>preferably closer to 100 and above. But it also depends on what reference was</div>
<div>active during recording, depending on the make of your nets.</div><div>For basic introductions you can</div><div>check out the links to various</div><div>resources for your education regarding re-referencing.</div><div>
<br></div><div><a href="http://dionysus.psych.wisc.edu/lit/Topics/Psychophysiology/CacioppoText/Ch.2.pdf" target="_blank">http://dionysus.psych.wisc.edu/lit/Topics/Psychophysiology/CacioppoText/Ch.2.pdf</a></div><div><ol>
<li><span style="color:rgb(119,119,204);font-family:arial,sans-serif;line-height:19px;white-space:nowrap;font-size:medium"><span style="font-size:small;font-weight:bold">[PDF]</span> from <a href="http://uni-konstanz.de" target="_blank">uni-konstanz.de</a></span></li>
<li><a href="http://www.springerlink.com/content/6785124141026861/fulltext.pdf" target="_blank">http://www.springerlink.com/content/6785124141026861/fulltext.pdf</a></li><li><a href="http://sccn.ucsd.edu/pipermail/eeglablist/2008/002510.html" target="_blank">http://sccn.ucsd.edu/pipermail/eeglablist/2008/002510.html</a> </li>
<li><span style="color:rgb(119,119,204);font-family:arial,sans-serif;line-height:19px;white-space:nowrap;font-size:medium"><span style="font-size:small;font-weight:bold">[PDF]</span> from <a href="http://tu-ilmenau.de" target="_blank">tu-ilmenau.de</a></span></li>
<li><a href="http://www.springerlink.com/content/6785124141026861/" target="_blank">http://www.springerlink.com/content/6785124141026861/</a></li><li><a href="http://onlinelibrary.wiley.com/doi/10.1111/1469-8986.3850847/abstract" target="_blank">http://onlinelibrary.wiley.com/doi/10.1111/1469-8986.3850847/abstract</a></li>
</ol></div><div><span style="color:rgb(68,68,68);font-family:verdana,arial,helvetica,sans-serif;font-size:11px;line-height:16px"><em><br></em></span></div><div><span style="color:rgb(68,68,68);font-family:verdana,arial,helvetica,sans-serif;font-size:11px;line-height:16px"><em><a href="http://www.mrc-cbu.cam.ac.uk/research/eeg/eeg_intro.html" target="_blank">http://www.mrc-cbu.cam.ac.uk/research/eeg/eeg_intro.html</a></em></span></div>
<div><span style="color:rgb(68,68,68);font-family:verdana,arial,helvetica,sans-serif;font-size:11px;line-height:16px">Electric potentials are only defined with respect to a reference, i.e. an arbitrarily chosen "zero level". The choice of the reference may differ depending on the purpose of the recording. This is similar to measures of height, where the zero level can be at sea level for the height of mountains, or at ground level for the height of a building, for example.</span><span style="color:rgb(68,68,68);font-family:verdana,arial,helvetica,sans-serif;font-size:11px;line-height:16px"><br>
</span><span style="color:rgb(68,68,68);font-family:verdana,arial,helvetica,sans-serif;font-size:11px;line-height:16px">For each EEG recording, a "reference electrode" has to be selected in advance. Ideally, this electrode would be affected by global voltage changes in the same manner as all the other electrodes, such that brain unspecific activity is subtracted out by the referencing (e.g. slow voltage shifts due to sweating). Also, the reference should not pick up signals which are not intended to be recorded, like heart activity, which would be "subtracted in" by the referencing. In most studies, a reference on the head but at some distance from the other recording electrodes is chosen. Such a reference can be the ear-lobes, the nose, or the mastoids (i.e. the bone behind the ears). With multi-channel recordings (e.g. >32 channels), it is common to compute the "average reference", i.e. to subtract the average over all electrodes from each electrodes for each time point. This distributes the "responsibility" over all electrodes, rather than assigning it to only one of them. If a single reference electrode was used during the recording, it is always possible to re-reference the data to any of the recording electrodes (or combinations of them, like their average) at a later stage of processing. In some cases "bipolar" recordings are carried out, where electrode pairs are applied and referenced against each other for each pair (e.g. left-right symmetrical electrodes).</span></div>
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<div><br></div><div><br></div><div><br></div><div><br></div><br><br><div class="gmail_quote">On Sun, Jan 15, 2012 at 10:02 AM, Marco Montalto <span dir="ltr"><<a href="mailto:montaltomarco@onvol.net" target="_blank">montaltomarco@onvol.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear all,<br>
<br>
I have collected data using a 32-channel EEG system. The electrodes were spread evenly on both hemispheres. These are the electrode locations: FPz, FP1, FP2, Fz, F1, F2, F3, F4, FCz, FC1, FC2, Cz, C1, C2, C3, C4, C5, C6, T7, T8, Pz, P1, P2, P3, P4, P5, P6, PO7, PO8, Oz, O1 and O2. The electrodes were referenced to left earlobe. In EEGLAB I have re-refrenced the data to average reference. I have reviewed the literature and found conflicting opinions as to whether re-referecing to average reference when using 32 channels is justifiable and defendable. Can anyone share his/her views regarding this matter? I am rather new to EEG so any help would be immensely appreciated. Thanks!<br>
<span><font color="#888888"><br>
Marco Montalto<br>
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