Introduction

What is EEG? What is EEG? what do you know?
"Newcomer Technician's Electroencephalogram Measurement Notes", where newcomer engineers who started in such a situation post what they felt when they actually touched the EEG.

I'm going to tell you a raw voice that challenges without prior knowledge.

Eye movement 2: Close and open one eye at a time

Last time (eye movement 1), we observed the electroencephalograph output during voluntary blinking, and explained how voluntary blinking affects the electroencephalograph and how to deal with it.
This was the act of closing and opening the left and right eyes at the same time.
Then, what kind of waveform can be observed when one side is closed and one side is opened?

Let's start measuring.

The measurement procedure was to close/open the eyes in the order of left eye, right eye, left eye, and right eye, and observed the electroencephalograph voltage at that time.
From the previous article (eye movement 1), the effect of eye movement becomes smaller as the distance from the eyeball increases.

From Graph 1, when the left eye is closed/opened, a remarkable voltage change is seen in the F3 electroencephalograph, and from Graph 2, when the right eye is closed/opened, a remarkable voltage change is seen in the F4 electroencephalograph.

Graph 3 is the superimposed EEG outputs of F3 and F4.
Since the experiment was conducted so that the left and right closing and opening timings are almost the same, the signals appear at equal intervals as intended.
The large and small signals are seen because the experiment was conducted one eye at a time.
As I introduced last time, this signal comes from the structure of the eye.

1. Structure of the eyeball
A structure in which the retina has a negative charge due to its resting potential, and the cornea consequently has a positive charge

2. Eye movement during blinking
The structure of the eyeball that faces upward when the eye is closed and faces forward when the eye is opened

Due to the above characteristics, when you close your eyes, electricity flows through your eyelids and propagates through your skin to your head.
Since an electroencephalograph, which is intended to observe only electroencephalograms, observes electrical signals, it captures artifacts caused by the opening and closing of the eyes, which are the same electrical signals.
The effect is large, and the voltage is more than 100 times that of the electroencephalogram signal.

Countermeasures/Requirement of countermeasures/Difficulty of countermeasures

【measures】
Since the magnitude and frequency of the signal change from time to time, try to remove it with a general-purpose filter, etc. If it is still difficult to remove it, discard the data for that period.
As a preliminary experiment, we asked the subjects to intentionally blink, and used it for the above measures.

[Necessity of measures]
Required

[Countermeasure difficulty]
During ~

Related information

New Technician's Electroencephalogram Measurement Record ~Artifact ② Eye Movement 1 Blink~

How to choose an electroencephalograph (EEG)

New Technician's Electroencephalogram Measurement Notes Extra Edition (Supplement)

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