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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
cite="mid:557D1652-0689-4111-B147-EA89068E4F08@ucdavis.edu"
type="cite">
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<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">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">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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<div style="margin: 0px;">--------------------------------------------------------------------</div>
<div style="margin: 0px;">Steven
J. Luck, Ph.D.</div>
<div style="margin: 0px;">Director,
Center for Mind &
Brain</div>
<div style="margin: 0px;">Professor,
Department of Psychology</div>
<div style="margin: 0px;">University
of California, Davis</div>
<div style="margin: 0px;">Room
109</div>
<div style="margin: 0px;">267
Cousteau Place</div>
<div style="margin: 0px;">Davis,
CA 95618</div>
<div style="margin: 0px;">(530)
297-4424</div>
<div style="margin: 0px;">E-Mail: <a
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<div style="margin: 0px;">Web: <a
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