6.
A ppl y ing t he Headset and Opt imizing Sensor Cont act
6.2 Optimizing Sensor Contact
After properly positioning the headset on the subject, the next step is to obtain
su
#
cient contact on all sensors before proceeding with the EEG recording. For
this step, you will need to bring up the impedance check in the Cognionics Data
Acquisition software under the Channels tab. The impedance check presents
a color coded map of the sensors in the headset. The color on each position
corresponds to the level of contact:
•
Red
- Unacceptable impedance (
>
5,000
k
!
)
•
Light Green
- Marginal impedance (2,500-5,000
k
!
)
•
Dark Green
- Acceptable impedance (
<
2,500
k
!
)
The range of impedances with dry electrodes may be much higher than what
you are accustomed to when working with conventional wet electrode amplifiers.
Cognionics headsets utilize a combination of advanced electronics, shielding and
mechanics to obtain EEG signals even when the contact is poor and can tolerate
electrode impedance of up to a few megaohms.
When setting up the headset, focus first on bringing all of the sensors in the
array to at least a marginal (light green) level of impedance, which means that
all of the electrodes are physically touching the scalp. Then focus on specific
positions until all of the impedances are at a fully acceptable level (dark green).
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