EEG
MEG
Information for MEG experimenters. (by Yuval)
Try to take participants who do not have metalic implants
(including dental). Do not run MRI before MEG on the same day.
Participants should not wear the following:
electronic / metalic devices: watch, phone,
keys, coins, buttons, zippers etc. (mainly on the shirt), shoes, belts,
bras with metallic parts, hair spray, make-up.
Experimental setting
The participant can talk and hear the experimenter, he can
activate an alarm if is in fear, or get out of the room by pressing a
big
red button near the door. A video monitor enables the experimenter to
see the participant throughout the experiment (even in a dark room
by using an IR camera).
Measurements can be taken in seated or supine position. The projector
screen can be adjusted for both positions. Ear phones (air tubes)
can be used for auditory stimulation.
EEG can be recorded in addition to the MEG, it requires about an hour
preparation time in addition to the 20min preparation time of the MEG.
The EEG system can be used for EMG,EOG or ECG recordings.
Other optional facilities:
- Eye tracker
- video recorder (not synchronized with the time series data)
- finger tactile stimulator (4 fingers per acquisition)
- response boxes (10 buttons)
- light detector on the screen to define the onset time of visual stimuli
- line power measuring device, for later cleaning of the 50Hz noise
We use E-prime to control stimuli, though other software can be used from a laptop or other computer with a parallel port.
Acquisition parameters
Sampling rate: There is no difficulty with 2kHz or less. Depending on the number of channels to be recorded, the sampling rate can be as high as 8kHz.Online filters and weights: acquisition is possible with 1Hz highpass (recommended for reducing low frequency effects of elevators) or with no highpass filter (DC). Lowpass filtering is flexible and depends on the sampling rate.
Reference channels which are located away from the head can sense environmental noise. Online cleaning of the data before digitization of the signal is recommended (analog weights). Digital weights can also be applied online though we recommend to apply digital weights offline, based on a noise measurement, taken with no subject in the room.
