[Eeglablist] the component direction in ASA and EEGLAB

[Ruud Kalis]

Dear Malahat, 

The visualization of ERP / EEG traces in the ASA software uses the convention that negative signals are plotted on the positive y-axis. This convention is quite standard for biosignals. ASA has an button in the EEG toolbar to switch the polarity. Please contact support at ant-neuro.com if you need more information about how to do this.

In EEGLAB / Matlab data is generally plotted in the "normal" way where negative signals are plotted on the negative y-axis. Multiplying your EEG.data matrix with -1 would flip the signals so they will look the same as in ASA. But the values would not be correct anymore. Please keep this in mind. I assume that it is possible to flip an axis in Matlab rather then multiplying with -1. Something like: set(gca, 'YDir', 'reverse'). 

Some of the reason why ERPs are plotted with negative upwards were explained by Frank Duffy, M.D. on the EEGLAB mailinglist:
http://sccn.ucsd.edu/pipermail/eeglablist/2011/004094.html

Best regards,
Ruud Kalis

----- Original Message -----
From: "malahat akbarfahimi" <malahatfahimi at gmail.com>
To: eeglablist at sccn.ucsd.edu
Sent: Saturday, 5 May, 2012 7:58:48 PM
Subject: [Eeglablist] the component direction in ASA and EEGLAB



Hi, 
I am working on ERP by ANT -ASAlab -and because of some problem I have imported my data in EEGLAB.In the .cnt in ASA , the positive component is down and vise verse, but when I opened the files in EEGLAB the direction were opposite, it means the positive components seems were in the up , so my question is , is it possible that in EEGLAB the direction were changed by multipleing negative, I am lookforward, 
regard 
-- 

Malahat Akbarfahimi 
Occupational Therapist-Ph.D Student of cognitive neuroscience 
Faculty Member 
Occupational Therapy Department-Rehabilitation Faculty 
Tehran University of Medical Science 
Iran-Tehran 



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-- 
Ruud Kalis
Sales and Support Germany
ANT (Advanced Neuro Technology)
eemagine GmbH, Berlin, Germany
T: +49 (0) 163 79 16 114
F: +31 (0)53 430 3795
I: www.ant-neuro.com
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