[Eeglablist] Positive "direction" switches between envtopo and erpimage?

[Scott Makeig]

Keith -

envtopo() shows the component polarity expressed in the data at the
indicated time point...
erpimage() by default shows the default component polarity (arbitrary but as
decomposed).

Reverse the indicated scalp map polarity in erpimage by specifying
-1*scalp_map. But then you should also reverse the polarity of the
activations (-1*data) -- *unless* you use the 'projchan' option to
pop_erpimage(), which plots (actual) uV at the requested scalp channel.
Clear?

Scott Makeig

On Mon, Sep 14, 2009 at 11:55 AM, Keith Yoder <kjyoder at gmail.com> wrote:

> Hi all,
> Sometimes it seems that envtopo and erpimage have different conventions for
> specifying which direction is positive when generate plots.  For example,
> I've attached two images generated from the same dataset.  In
> 'S01_PCA3.png', the third component is registering as "positive-up" i.e. the
> positive topography is oriented towards the top of the head.  However, the
> ERP plot for component 3 seems to have switched 'S01_PCA3_ERP_Comp3.png.'
>  This has proven to be inconvenient when examining multiple components in
> multiple conditions.  Has anyone encountered this before?  Is there a way to
> force envtopo and erpimage to produce plots with positive oriented in the
> same direction?
> Thanks,
> Keith
> --
> Research Aide
> Belmonte Autism Lab
> Cornell University
>
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation, University of
California San Diego, La Jolla CA 92093-0961, http://sccn.ucsd.edu/~scott
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