[Eeglablist] EEGLab, BioSemi ActiveTwo mk2 and event markers

[Lloyd Smith]

Resending message below due to failure message...

____________

 

Hi, Bill.  I hope you don't mind that I posted this reply to the EEGLAB
list, too.  I BCC'd you to keep your e-mail private.

 

This problem is reported to me at least once a week by EEGLAB users - it
is a known issue in EEGLAB that all ActiveTwo/EEGLAB users are grappling
with one-at-a-time.

 

Triggers in ActiveTwo are stored on the Status channel.  Status is a
24-bit channel with 16 bits for the trigger input port and an additional
8 bits for internal status codes (e.g. battery low/OK, CM out-of/in
range, etc.).  The code 33536 indicates that all bits of the least
significant byte of the status channel are zero, but some bits of the
middle byte of the Status channel are high (i.e. 1000001100000000).  In
most cases, we deliver a simple 8-bit trigger cable for use with
Presentation/E-Prime that shorts the middle byte of the status channel
to zero, so a value of 33536 would not be possible.  If you are using
our standard 8-bit trigger cable, then this value is spurious (generated
by EEGLAB or BIOSIG), and you can ignore it or mask it by applying a
bitmask to the events from the MATLAB command line.  

 

FYI -- see also
http://www.sccn.ucsd.edu/pipermail/eeglablist/2005/001158.html for a
description of the BDF Status channel that explains how the valuable
status data (cm in/out-of range, battery low/OK, etc) are encoded in the
Status channel.  I believe that these useful pieces of information are
still ignored by EEGLAB, but it would be nice if they were properly read
and encoded.

 

Hope that is helpful.

 

Lloyd Smith

Owner

Cortech Solutions, LLC

 

Cell: 910-431-2811

E-mail: LSmith at cortechsolutions.com

 

321 N. Front Street, Suite 113

Wilmington, NC 28401 USA

Office: 910-362-1143

Fax: 910-362-1147

 

  _____  

From: William _
Sent: Monday, June 25, 2007 11:20 AM
To: Lloyd Smith
Subject: question about event code

 

Hi Lloyd,

 

When we read in our data using EEGLAB, we get an event code "33536" that
seems to correspond to event offsets.  I think when you were here you
told me how to avoid these, but I can't remember what you said. Does
this sound familiar?

 

Thanks,

 

Bill

 

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