Check Your Signal: Step by Step

by Tonny Mulder

CHECK SIGNAL

Introduction

In this tutorial you will check the quality of your signal and examine the artifacts that may reside in your recording.



Select what you want to do, by clicking on the pictures of your choice

CHECK SIGNAL

Connecting your participant.

To use this tutotial it is first necessary to connect a participant.

Setup a recording for Fz, Pz and Oz locations. Fill the cap with the three red recording electrodes, one yellow ground electrode on Cz and connect the blue earlobe reference when the cap is on the head of the participant. If necessary, use the setup page for reference

placement

Fitting the cap.

gelling

Select the cap size that fits your subject. 

The blue cap is the largest, the red one has a medium fit and the green one is the smallest. The cap should be tight enough so the electrodes are close to the scalp but still comfortable for the subject to wear. Let the subject put on the cap.

Orienting the cap

  1. Measure the head size of the subject from nasion to inion, and from the left tip of the ear to the tip of the right ear.
  2. The location of the Cz electrode should be in the center of these measures.
  3. Move the cap around if necessary and make sure it fits tight and symmetrical.
  4. Let the subject place the chin band.
  5. Now you are ready to gel the electrodes.

Gelling electrodes.

gelling gellingref

Gelling the electrodes

  1. Fill the curved syringe with electrode gel.
  2. Place the tip of the syringe through the electrode on the skull. Ask the subject whether he/she feels the tip.
  3. Apply the gel while retracting the syringe.
  4. Apply the gel while retracting the syringe.
  5. The reference electrode (blue clip) is gelled by appying a drop of gel on the metal electrode disk and place it on one of the ear lobes.
CHECK SIGNAL

Introduction

Use this signal check pipeline when you have a participant hooked up and you are ready to record.

In this tutorial you will check the quality of your signal and examine the artifacts that may reside in your recording.


PRESS START in the EEG_Recorder Window.

What Happened?

NO CONNECTION

No Connection with the MobiLab.

The Situation Diagnosis Solution
1 The MobiLab is not plugged in Cable is not connected Press Clear, Plug MobiLab in, Press Start
2 The MobiLab is not switched ON The MobiLab is not switched ON Press Clear, Switch MobiLab ON, Press Start
3 The MobiLab is switched ON but LED is blinking red The MobiLab batteries are dead Press Clear, Change MobiLab Batteries, Press Start
4 The MobiLab is switched ON and LED is blinking green Driver issue Restart Matlab and EEG_Recorder and try again
5 None of the above HELP! Contact the assistant

Now the recording should start

Continue with section: Recording started!

RECORDING STARTS

Recording Starts.

The Situation Diagnosis Solution
1 ALL channels are bad GammaBox is still OFF Switch GammaBox ON
GammaBox is ON but no Green light Change the battery for the GammaBox
Yellow ground electrode and/or blue reference electrode are not connected Connect Ground and reference electrodes. Dont forget the GEL
No Gel into red recording electrodes GEL all electrodes, make sure no air is trapped between the gel and the skull
ALL Electrode Plugs not properly connected to GammaBox Push Plugs in to the hilt
Still none of the recording electrodes work Change the Yellow grond and/or the Blue reference electrode
2 A few channels are bad, the rest is okay! Ground and reference electrodes work, some recording electrodes don't. GEL the faulty recording electrodes
Still a few recording electrodes don't work properly Push Plugs of faulty electrodes into the GammaBox
Still a few recording electrodes don't work properly Change the electrode (s) in question

Now that all channels provide a signal, it is time to start finetuning

Continue with section: Fine Tuning

Now that all channels provide a signal, it is time to start your first EEG recording

Continue here with the demo experiment

Go to the demo-experiment

Fine Tuning your signal

Fine Tuning your Signal.

During the recording, your EEG signal can become contaminated by sources other than from the brain, such as the mains grid (our electricity network), all kinds of muscle tension artifacts and various other interferences. The first produces a high-amplitude 50 Hz artifact (60 Hz in the USA), often ‘repeated’ at the multiples of the frequency (at 100 Hz, 150 Hz and so on). Furthermore, low frequency drifts can obscure your data.

The first step in getting a clean recording is to get rid of these contaminations. There are a few ways to do this.

Discuss with your teaching assistent how to get the best results.