[Eeglablist] EEG amplifier and alternative input

Ross Fulham Ross.Fulham at newcastle.edu.au
Tue Aug 3 17:47:04 PDT 2010


Marc,

The first question is what do you intend doing with the voice response? Are you hoping to measure reaction time; Do you want to be able to play it back and understand what was said?

(a) EEG is typically recorded at 500-1000 Hz. This is way below the sampling rate used to record hi-fidelity voice/music (44000Hz). With 1000Hz sampling the recorded voice will be uninterpretable, though you might be able to rectify the signal; obtain the envelope of the voice waveform; and extract a reaction time measure. The most accurate way to do this is to use an electronic circuit to rectify the signal coming from the microphone, then low-pass filter it before feeding it into the EEG headbox.

(b) Connecting any inputs into the EEG headbox other than the electrode wires (1) causes safety issues if the device is not properly electrically isolated; (2) may introduce electrical artifacts into the EEG recordings.  If your microphone setup requires any type of electrical power, make sure it is battery powered and not connected to the mains supply.

(c) having subjects make a vocal response is going to introduce all manner of movement related artifacts into the EEG recordings, some of which will be time-locked to your stimuli.

If all you want is to measure voice related reaction times, there are devices available that are designed for this purpose and are connected to the stimulus generation system in the same way a push-button response is recorded.

Ross
 

>>> Marc <maarcc at gmail.com> 04/08/10 4:12 AM >>>
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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