[Eeglablist] the component direction in ASA and EEGLAB

[Arnaud Delorme]

Dear Ruud,

you may also edit the file "icadefs.m" and change the option YDIR at the beginning. However, I am not sure this parameter is taken into account in all EEGLAB ERP plotting functions. Most ERP function also have an optional 'ydir' option you can use to reverse ERP polarity. On the EEGLAB graphic interface, you can usually enter 'ydir',-1 to obtain the desired effect in the optional parameter window.

Best,

Arno

On May 7, 2012, at 4:20 AM, Ruud Kalis wrote:

> 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 
> 
> 
> 
> _______________________________________________
> 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
> 
> -- 
> 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
> ===
> This message, including attachments, may contain confidential information that is proprietary and/or legally privileged. If you are not an intended recipient, or a person responsible for delivering it to the intended recipient, please notify the sender and then delete and destroy the original message and all copies. You should not copy, forward, or disclose this message, in whole or in part, without permission of the sender. Thank you for helping us to maintain the confidentiality of this information.
> _______________________________________________
> 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