From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2001-12-04 20:57:06
Dear Andreas:
I am so glad that program worked for you. I was not sure about how to upload and download stuff.
It has been a few years so bear with me. The one channel looks at F1 and O1 and the other looks at F2 and O2. The ground reference is on each templeon the hair line. The placement follows the Mind Mirror convention exceptthey use the middle of the forehead as the ground.
This system is a sort of active electrode as discussed by Doug. The preamp. is attached to a belt at the waist. The input is shielded audio RCA cable going to a headband with Velcro fasteners. The electrodes are also shielded. The output is run through standard 6 conductor unshielded telephone wire to the HC11 module. With this setup you can walk around the house andnot have to lie down and be still. There are no wire movement artifacts.
The 60 Hz pickup you see is a minor annoyance and I have spent considerabletime to eliminate it. I did not choose the conventional solution of a notch filter at 60 Hz or a steep roll-off of the high frequency end because I did not want to throw away possibly valuable data. I was exploring alteredstates and not just bio feedback training Alpha.
What you call muscle artifacts may be much more than you think. I had to DC coupled the input stage so I could get clean and accurate .5 to 2 Hz signals. Look at the Downey file. These are the brain waves of a very gifted and quite accurate medium. I am a real doubting Thomas and it takes a lot to convince me. He had access to information that I had to call my mother to confirm. Very impressive and quite humble. He allowed me to test him several times. When he was in his mediumistic state he produced massive high amplitude Delta waves.
There is a problem with common mode rejection. The circuit that I use allows you to get infinite common mode rejection by adjusting the balance pot. BUT that assumes a balanced source resistance. Logic would tell you that if you had a very high input impedance input amp that would not be a problem. After a lot of experimenting, I had to install a 10 Meg ohm input resistor to ground. The other problem is the electrode source impedance. When you start it is easy to get 10 K ohm with conductive paste. For medical orclinical settings that is no problem. But if the person tested goes into an altered state, the skin resistance changes and the conductive paste has no effect. This is why you saw the 60 Hz effect change during the session.The other problem that the theorist on the group don't realize is that the best common mode rejection amps only cancel common mode noise. The electrodes are actually connected to two "antennas", meaning the body. Unless both antennas pick up exactly the same noise, there is no cancellation and you get the difference of the two noise sources. In a meditative state the skin resistance will rise to 100 K ohms and sometimes several meg ohms. The two differential electrodes do not see the same source. Therefore the common mode specs may be meaningless.
Please tell me more about your application, maybe I can help.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: sleeper75se_at_yahoo.se
To: buildcheapeeg_at_yahoogroups.com
Sent: Tuesday, December 04, 2001 2:17 PM
Subject: [buildcheapeeg] Re: Group feedback
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Andreas:
>
> Were you able to get my software (slink12r) to run on your computer?
>
Hello Jim,
yes it worked without any problems whatsoever. Gave me a DOS-
flashback. :-)
Just curious, what were the circumstances for the sessions? Was the
subject (you, I presume) lying down etc. and how were the electrodes
placed? There was a fair bit of muscle noise periodically, and at
some points, the 60Hz hum changed in amplitude a bit. I'm trying to
get a handle on how to minimize those kinds of problems for my
particular application (meditation training).
/Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:32 BST