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Dear Teresa,<br>
<br>
Scalp potentials were usually not related to dipoles at the time the
convention originated.<br>
<br>
Early texts are, for instance, Caspers H Speckmann EJ Lehmenkuehler
A (1987, Rev Physiol Biochem Pharmacol 106:127-178), and Birbaumer
N, Elbert T Canavan AGM Rockstroh B (1990, Psysiol Rev 70:1-41)<br>
<br>
Later texts (e.g. the PIzzagalli chapter in the Handbook of
Psychophysiology 3rd Ed) are usually less explicit on this issue.<br>
<br>
Best,<br>
Geert<br>
<br>
Op 17-06-11 22:03, Teresa Hawkes schreef:
<blockquote
cite="mid:BANLkTimowVrSbwsk23+enit_YJvHm7ja5A@mail.gmail.com"
type="cite">
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Dear List,
<div><br>
</div>
<div>I was under the impression that positive deflections reflect
dipoles moving toward an electrode and negative deflections
reflect dipoles moving away from an electrode. I would be
interested in seeing the evidence correlating negative
potentials with cortical activation and positive potentials with
cortical inhibition.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Teresa Hawkes</div>
<div>University of Oregon<br>
<br>
<div class="gmail_quote">On Thu, Jun 16, 2011 at 6:55 PM, Geert
van Boxtel <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:G.J.M.vBoxtel@uvt.nl">G.J.M.vBoxtel@uvt.nl</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;">
<div text="#000000" bgcolor="#ffffff"> Dear list,<br>
<br>
The historical "accidents" that Steve describes actually
had a sound basis in neurophysiology in that negativity
measured at the scalp was supposed to reflect cortical
activation, whereas positivity measured at the scalp was
thought to reflect cortical inhibition, both at the level
of postsynaptic potentials (EPSPs and IPSPs,
respectively). Much research in the 1960s focused on three
types of ERPs: the negative Contingent Negative Variation
(CNV) and Readiness Potential (RP), and the positive P300.
For the CNV and RP, an increase in negativity meant an
increase in cortical activity, so it made perfect sense to
plot these potentials negative-up.<br>
<br>
Nowadays, the convention originating from physics to plot
positivity upwards is becoming more and more current. Of
course, polarity depends on the reference used in the
recording, so it should be considered good science to be
able to think both negative-up and positive-up.<br>
<br>
Best regards,<br>
Geert<br>
<br>
<br>
<br>
Op 16-6-2011 21:42, Steve Luck schreef:
<blockquote type="cite">
<div>
<div class="h5">
<div>Mehmet-</div>
<div><br>
</div>
<div>The polarity conventions in ERP research are
arbitrary and partially reflect historical
accidents. You can plot negative upward if you
mainly want to communicate your results to people
who are used to looking at ERPs with negative
upward. You should plot positive upward if you
mainly want to communicate your results to the
99.999999% of scientists who use the Cartesian
convention of plotting positive upward.</div>
<div><br>
</div>
<div>Steve</div>
<div><br>
</div>
<div><br>
<blockquote type="cite"><br>
<div style="margin: 0px;"><span
style="font-family: 'Helvetica'; font-size:
medium; color: rgb(127, 127, 127);"><b>From:
</b></span><span style="font-family:
'Helvetica'; font-size: medium;">mehmet ali
<<a moz-do-not-send="true"
href="mailto:theretinaguy@gmail.com"
target="_blank">theretinaguy@gmail.com</a>><br>
</span></div>
<div style="margin: 0px;"><span
style="font-family: 'Helvetica'; font-size:
medium; color: rgb(127, 127, 127);"><b>Date:
</b></span><span style="font-family:
'Helvetica'; font-size: medium;">June 16,
2011 5:29:38 AM PDT<br>
</span></div>
<div style="margin: 0px;"><span
style="font-family: 'Helvetica'; font-size:
medium; color: rgb(127, 127, 127);"><b>To: </b></span><span
style="font-family: 'Helvetica'; font-size:
medium;"><a moz-do-not-send="true"
href="mailto:eeglablist@sccn.ucsd.edu"
target="_blank">eeglablist@sccn.ucsd.edu</a><br>
</span></div>
<div style="margin: 0px;"><span
style="font-family: 'Helvetica'; font-size:
medium; color: rgb(127, 127, 127);"><b>Subject:
</b></span><span style="font-family:
'Helvetica'; font-size: medium;"><b>[Eeglablist]
p300 convention</b><br>
</span></div>
<br>
<br>
Hi all,<br>
<br>
p300 is conventionally plotted on an inverted
axis( positive potentials to down), is there a
reason to end up with this convention?<br>
<br>
Best,<br>
<br>
<br>
<br>
<br>
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Center for
Mind &
Brain</div>
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Department of
Psychology</div>
<div
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<br>
<br clear="all">
<br>
-- <br>
Teresa D. Hawkes, B.F.A.<br>
Ph.D. Candidate<br>
Department of Human Physiology<br>
University of Oregon<br>
348 Gerlinger Hall,<br>
1240 University of Oregon<br>
Eugene, Oregon 97403-1240<br>
Phone: 541-337-9443 (cell) or 541-346-0275 (laboratory)<br>
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