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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Dear Neha,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I have recently been dealing with exactly the same problems as
you describe. I am running an attention experiment that requires subjects to
maintain fixation at the center of the screen, so I am using the EOG to measure
eye movements in order to throw away trials where central fixation is not
maintained. I’ve been using a paper on biofeedback systems to assist with
this.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Barea et al (2002) , writing in IEEE, state that the the
following:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>The EOG signal changes
approximately 20 microvolts for each<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>degree of eye movement. In
our system, the signals are sampled<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>10 times per second. The EOG
signal is a result of a number of<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>factors, including eyeball
rotation and movement, eyelid movement,<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>different sources of artifact
such as EEG, electrode placement,<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>head movements, influence of
the illumination, etc. It is<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>therefore necessary to
eliminate the shifting resting potential<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>(mean value) because this
value changes. To avoid this problem<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>an ac high-gain differential
amplifier (1000–5000) is used, together with a high pass filter with
cutoff frequency at 0.05 Hz<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>and relatively long time
constant and a lowpass filter with cutoff<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>frequency at 35 Hz. Ag-AgCl
floating metal body-surface electrodes<o:p></o:p></span></p>
<p class=MsoNormal style='text-autospace:none'><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'>are also used.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I am currently trying to determine how tightly coupled the
magnitude of change in the EOG channels and the actual change in eye fixation,
measured in degrees, and whether I can determine precisely where the eyes are
given the EOG amplitudes.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Anyone else have other suggestions or literature recommendations
that could be helpful?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><br>
Thanks<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Andre<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> eeglablist-bounces@sccn.ucsd.edu
[mailto:eeglablist-bounces@sccn.ucsd.edu] <b>On Behalf Of </b>neha bhutani<br>
<b>Sent:</b> Sunday, October 21, 2007 9:00 PM<br>
<b>To:</b> eglablist-bounces@sccn.ucsd.edu; eeglablist@sccn.ucsd.edu<br>
<b>Subject:</b> [Eeglablist] Baseline problem<o:p></o:p></span></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><br>
<br>
<o:p></o:p></p>
<div>
<p class=MsoNormal>Dear users,<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> I am very new to the EEG recordings. I am working on
the presaccadic potentials and am not able to understand some of the very basic
problems. It would be of great help if any one of you can kindly help me with
it. In my recordings after a saccade is over the hEOG channel activity doesnot
come to the baseline. When I plotted the whole hEOG channel in MATLAB I found a
constant drift in the hEOG channel. Is this normal to happen? Or if not, then
what measures should I take to remove this drift? <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> Moreover when I try to analyze my data I find most of
my channels being contaminated with the very high saccadic potentials. How
should I proceed to ensure that I am able to correctly remove this
contamination from the other channels and still get the presaccadic potentials?
<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>One more thing which I want to ask is, that since in my
recordings, there is no input to the system when the subject is making a
response (in the dat file) how should I proceed to calculate the reaction
times, as I want to separate my trials based on slow and fast reaction times? <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>I would be happy if any one can give comments and
suggestions regarding my problems. <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>Thanks in advance.<br clear=all>
<br>
-- <br>
Neha Bhutani<br>
Graduate Student<br>
Cognitive Neuroscience<br>
National Brain Research Centre<br>
Manesar, India <o:p></o:p></p>
</div>
<p class=MsoNormal><br clear=all>
<br>
-- <br>
Neha Bhutani<br>
Graduate Student <br>
Cognitive Neuroscience<br>
National Brain Research Centre<br>
Manesar, India <o:p></o:p></p>
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