[Eeglablist] Re-referencing to Average Reference

[Tarik S Bel-Bahar]

 The polar *average reference *effect: a bias in estimating the head
surface integral in EEG
recording<http://www.sciencedirect.com/science/article/pii/S1388245799000449>
[PDF] from uni-konstanz.de<http://kops.ub.uni-konstanz.de/bitstream/handle/urn:nbn:de:bsz:352-opus-19025/Junghoefer_et_al_1999_PARE.pdf.pdf?sequence=1>
M Junghöfer, T Elbert, DM Tucker… - Clinical Neurophysiology, 1999 -
Elsevier
*...* that the voltage time series reflects the difference in electrical
potential between two *electrodes*. *...*
spatial derivative, such that current density measures with 19- or *32*-channel
recordings *...* The
question for practical EEG recording is whether an *average*
*reference* fulfils
the criterion *...*
Cited by 118<http://scholar.google.com/scholar?cites=17137298841162271237&as_sdt=2005&sciodt=0,5&hl=en>
 - Related articles<http://scholar.google.com/scholar?q=related:BcowrX_q0-0J:scholar.google.com/&hl=en&as_sdt=0,5>
 - Library Search <http://www.worldcat.org/oclc/315430049> - All 12
versions<http://scholar.google.com/scholar?cluster=17137298841162271237&hl=en&as_sdt=0,5>
 Spatial sampling and filtering of EEG with spline laplacians to estimate
cortical potentials <http://www.springerlink.com/index/R086736518RG8172.pdf>
[PDF] from tu-ilmenau.de<http://www.tu-ilmenau.de/fakia/fileadmin/template/startIA/bmti_neu/div/HS/neues_layout/bmt/srinivasan_BT_1996_EEG_spatial_sampling.pdf>
R Srinivasan, PL Nunez, DM Tucker… - Brain Topography, 1996 - Springer
*...* Mapping the potential field is the most typical approach in studies
of EEG topogra- phy, typically
recorded with less than *32* *electrodes*, and often confounded by the
assumption that a *...* The potential
field can be mapped with respect to the *average* *reference* (Bertrand et
al. *...*
Cited by 122<http://scholar.google.com/scholar?cites=7605044994983867216&as_sdt=2005&sciodt=0,5&hl=en>
 - Related articles<http://scholar.google.com/scholar?q=related:UDPgMiGMimkJ:scholar.google.com/&hl=en&as_sdt=0,5>
 - BL Direct<http://direct.bl.uk/research/2A/19/RN010705691.html?source=googlescholar>
 - All 7 versions<http://scholar.google.com/scholar?cluster=7605044994983867216&hl=en&as_sdt=0,5>




On Tue, Jan 17, 2012 at 11:52 PM, Tarik S Bel-Bahar <tarikbelbahar at gmail.com
> wrote:

> 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,
> preferably closer to 100 and above. But it also depends on what reference
> was
> active during recording, depending on the make of your nets.
> For basic introductions you can
> check out the links to various
> resources for your education regarding re-referencing.
>
>
> http://dionysus.psych.wisc.edu/lit/Topics/Psychophysiology/CacioppoText/Ch.2.pdf
>
>    1. [PDF] from uni-konstanz.de
>    2. http://www.springerlink.com/content/6785124141026861/fulltext.pdf
>    3. http://sccn.ucsd.edu/pipermail/eeglablist/2008/002510.html
>    4. [PDF] from tu-ilmenau.de
>    5. http://www.springerlink.com/content/6785124141026861/
>    6.
>    http://onlinelibrary.wiley.com/doi/10.1111/1469-8986.3850847/abstract
>
> *
> *
> *http://www.mrc-cbu.cam.ac.uk/research/eeg/eeg_intro.html*
> 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.
> 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).
>
>
>
>
>
>
> On Sun, Jan 15, 2012 at 10:02 AM, Marco Montalto <montaltomarco at onvol.net>wrote:
>
>> Dear all,
>>
>> 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!
>>
>> Marco Montalto
>> _______________________________________________
>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>> To unsubscribe, send an empty email to
>> eeglablist-unsubscribe at sccn.ucsd.edu
>> For digest mode, send an email with the subject "set digest mime" to
>> eeglablist-request at sccn.ucsd.edu
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20120117/85c8a65a/attachment.html>