[Eeglablist] EEG amplifier and alternative input

[Jack Shelley-Tremblay]

Also, don't forget that you are introducing all of the artifact associated with

speaking (EMG, movement, etc...).

If you are trying to correlate EEG with ongoing speech you must

address the EEG artifact issues first, I would say.

Also, with any decent digital recording software, even shareware, you

will get a time code, and this could be sequenced to your EEG time code

quite easily. Probably would be better to record speech in a separate program, in

my opinion.


There are two major issues, both related to the differences in EEG and 
voice spectral content:

1. EEG amplifiers typically record from 0.5 -100 Hz but may be able to 
open to 500Hz for EP data collection. However, voice typically requires, 
for telephone-like reproduction, a 500 Hz to 3000 Hz band pass. Thus the 
EEG amplifiers would likely reject and/or severly distort audio inputs.
2. As most EEG machines are digital these days, they time sample 
(digitize) EEG signals. As a minimum they must use a rate that is 
slightly more than twice the highest desired input signal, e.g., 200 H 
samplige rate for 100 Hz EEG.  For voice one would require a 
digitization rate of at least 2x 3000Hz; typically one wants a minimum 
of 10000 Hz for voice.  So the EEG devices typical sampling rates of 
200-1024 Hz would not reasonably sample voice signals.

So, no, voice over EEG amplifiers won't work. It would take a complex, 
parallel EEG and separate voice amplifier and A-D converter setups to 
match voice to EEG. This can be done. Indeed some EEG machines match 
both voice and video to EEG. However, there is a lot of engineering to 
make the EEG and voice/video follow the same clock time.

Best of luck.

Frank Duffy, MD  fhd at sover.net 
For the above discussion also BSEE and ham (k1moq)
On 8/3/2010 8:10 AM, Marc wrote:
> Hi.
>
> This is not directly related to EEGLab. But I thought someone may be
> able to give some pointers.
>
> We're doing some experiments measuring scalp EEG of participants. One
> of the variables we intend to record is the participant's voice reply.
> We're wondering if it is possible to use the same EEG hardware
> amplifier to record the voice reply? Have anyone tried that before?
> That is, instead of connecting the electrodes to the one of the 64
> channels of the amplifier, we connect a microphone to the input
> channel. I assume we will be able to record as good a signal as any
> audio amplifier? Is there any thing else to watch out for?
>
> Thanks for any advise.
>
> Marc.
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John Shelley-Tremblay, PhD
Associate Professor
Department of Psychology
307 University Blvd. North
University of South Alabama
Mobile, AL 36688-0002
251-460-6883

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