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1189Re: [buildcheapeeg] Re: Alpha/Theta feedback

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  • Joerg Hansmann
    Sep 10, 2001
      Hi,

      ----- Original Message -----
      From: <peterson@...>
      To: <buildcheapeeg@yahoogroups.com>
      Sent: Wednesday, September 05, 2001 3:34 AM
      Subject: [buildcheapeeg] Re: Alpha/Theta feedback


      > Joerg--Glad to hear you are playing with alpha-theta. Yes. A2
      > (actually Au2) would be the right earlobe. If your other electrode
      > is at Cz I imagine you could use your left earlobe (Au1) instead if
      > you wanted to, with no particular difference in effect.

      That would be interesting to verify with a 2 channel device.
      (ch1:Cz-Au1, ch2:Cz-Au2)

      I have heard that often Au1 and Au2 are tied together.

      > Many people--I suppose most--are able to produce stronger alpha than
      > theta. You should set the theta threshold separately, not use the
      > same one as for alpha.

      I have now implemented this feature in the comEEG SW.

      > You will need to experiment to get the right
      > threshold, but it should be one that provides feedback about 25% of
      > the time for theta.

      How is this threshold adjustment done in professional NFB SW ?
      At the moment I can only imagine 2 ways to do this:
      1) manual threshold adjustment by trial and error.
      2) automatic adjustment at program start: For a defined period (a few minutes)
      the SW samples EEG-data and calculates the threshold to meet the 25%
      criterion.

      > Also as you get better at producing either alpha
      > or theta, you can set the threshold for that band up higher. If
      > you're exceeding an alpha threshold of 25 uV 90% of the time, set it
      > up a few microvolts til you're only exceeding threshold 50 or 60% of
      > the time.


      I will do this.

      With the fixed thresholds my NFB-experiments are getting boring and ineffective.


      > Also, traditionally, alpha-theta is usually trained at O1, which is
      > on the back of the head.

      I could imagine that in lying position O1 is susceptible for
      artifacts caused by varying pressure (head on cushion) on
      the electrodes.

      > Both the Greens and Peniston use(d) this
      > site. Find a bony bump at the back of your head about 3 or 4 cm from
      > the top of your neck. This bump is called the inion, and is a
      > beginning-point for locating EEG sites. O1 will be about 2.5 cm up
      > and 2.5 cm to the left of that bony protrusion.
      >
      > Actually, though, since you started training at Cz, there is probably
      > no reason to change now. At least one published alpha-theta study
      > used (if I remember correctly) C3 and got perfectly good results, so
      > probably anywhere from Cz back is OK.
      >
      > If you just want to train alpha, Pz is probably the best site, but
      > again Cz would be OK. Since you apparently aren't getting much
      > feedback on theta, you are probably actually doing alpha training in
      > effect.

      I do not know, how much Theta I would get with correctly adjusted thresholds.

      Therefore the next thing I will implement is some session statistics.
      This seems very important to me for tracking progress and to
      find the right adjustment for the feedback thresholds.



      Regards,

      Joerg
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