IEEE Systems, Man and Cybernetics Magazine - July 2020 - 23

flat, and sticker (disposable)-depending on their location
in the HMD. Silver/silver chloride (Ag/AgCl) dry flexible
electrodes [52] were used for EEG measurement in locations with the presence of hair. Flat Ag/AgCl dry electrodes [53] were implemented in places where contact
with bare skin is needed and the electrode is physically
supported by the HMD (i.e., around the face piece to
record EOG, facial EMG, and frontal EEG). Finally, standard Ag/AgCl disposable sticker electrodes were used on
bare skin where there was no support for the electrodes,
such as at the mastoids (reference) and on the left collarbone (for ECG acquisition). The three types of electrodes
are shown in Figure 1(c)-(e), respectively.
Hardware Integration
With the aim of using the 16-channel configuration to
record EEG, EOG, ECG, and facial EMG signals, we proposed acquiring 11 EEG signals from electrodes located
in three areas: frontal (Fp1, Fpz, and Fp2), central (FC1,
FC2, Cz, CP1, and CP2), and occipital (O1, Oz, and O2).
The EOG signals were derived from the EEG electrodes
on the frontal area as well as two vertical and two horizontal electrodes placed on the face piece of the HMD.
Facial EMG signals were also acquired from the electrodes on the face piece. Moreover, one electrode was
placed on the user's collarbone with the goal of acquiring
an ECG signal. Finally, the bias and the stimulus-reference-bias (SRB) terminals were placed on the mastoids.
For this proposed 16-channel configuration, the placement of the electrodes can be seen in the layout depicted
in Figure 3(a), and the face piece sensors are further

V EOG Left

shown in Figure 3(b). The layout can be easily modified
depending on the experimental protocol. The final prototype can be seen in Figure 4. Plots of the 16 signals
collected simultaneously are available as supplementary material.
Software Integration
The open-research philosophy behind the OpenBCI product line facilitates the integration of the developed system
with myriad programming languages and communication
protocols, including lab streaming layer, as well as open
tools, such as OpenViBE, MNE, and our in-house-developed Multimedia / Multimodal Signal A nalysis and
Enhancement Lab EEG server (MuLES) [34].
Validation of the Developed BMI-HMD
To validate the developed BMI-HMD, four validation scenarios were proposed for each of the acquired modalities.
A total of five participants wore the BMI-HMD under
these scenarios. In our experiments, the VR applications
were developed with Unity3D with synchronization using
MuLES. The detailed instructions to replicate the validation scenarios are available online [54].
Validation of the EEG Signals
A common paradigm in EEG experimentation is the
recording of SSVEPs, which are elicited in the visual cortex when a user gazes at a target that flickers at a specific
frequency. The spectral content of the SSVEPs corresponds to the frequency of the flickering target. As such,
the validation scenario for the EEG modality consisted of

V EOG Right
H EOG Right

H EOG Left
Fp1

Fpz

Fp2
Fp1

FC1

CP1

ECG

CP2

Oz

H EOG
Right

H EOG
Left

Disposable Electrode
Dry Flexible Electrode
Dry Flat Electrode

O1

Fp2

FC2
Cz

BIAS

Fpz

SRB
V EOG Left

V EOG Right

O2

(a)

(b)

Figure 3. The proposed layout for the 16-channel configuration: (a) top view and (b) the electrodes on the

face piece. H: horizontal; V: vertical.

	

Ju ly 2020

IEEE SYSTEMS, MAN, & CYBERNETICS MAGAZINE	

23



IEEE Systems, Man and Cybernetics Magazine - July 2020

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