p300 and emotiv epoc: does emotiv epoc capture real eeg? · p300 and emotiv epoc: does emotiv epoc...

P300 and Emotiv EPOC: Does Emotiv EPOC capture real EEG? By Hiran Ekanayake 2010

P300 and Emotiv EPOC: Does Emotiv EPOC capture real EEG?By Hiran Ekanayake

Important: Please note that an improved version of this document is now available at http://neurofeedback.visaduma.info/emotivresearch.htm

Part 1: Experiment and resultsPart 2: Experiment framework and tools

Part 1: Experiment and results

1. Experiment in brief

P300 (or P3) is one of the components in an ERP waveform (Illustration 2). It is a positive deflection in voltage (2-5μV) with a latency of about 300-600 ms from the stimulus onset. It is typically measured by placing electrodes covering the regions Fz, Cz and Pz (Illustration 1). Since the strength of an ERP signal is a very low it is usually hidden within the noise and not visible in a typical EEG recording. Therefore, to see the actual ERP waveform one has to bandpass filter the EEG signals (typically 1-20 Hz) and averaged over multiple trials (calls epochs, usually segments of -1000 ms and 2000 ms relative to each stimulus). The most popular experiment for obtaining P300 is called P300-speller (Illustration 3), which is a 6x6 matrix of alphanumeric characters where one of its rows or columns flashes randomly at a time in a sequence (also calls the odd-ball paradigm) while the subject is focusing on one of the characters in the matrix. Whenever the subject sees that the cell containing the character he/she is focusing flashes, the subject has to count the number of times that cell has flashed. After the experiment, the averaged epochs containing targets (flashings of focused cells) is compared against averaged epochs containing non-targets (other background flashes). What one would see is that average signal for epochs of targets forms an ERP waveform while for non-target epochs forms some kind of a random signal. However, random artifacts, such as from eye movements, within EEG recordings significantly distort the resulting ERP waveform. [1][2][3]

Experiment discussed in this document consisted of three separate sessions using one subject (male, 32).

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http://neurofeedback.visaduma.info/emotivresearch.htm


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Illustration 2: An ERP waveform and its components. Note the direction of positive signal downwards. (Wikipedia)

Illustration 1: The 64-channel electrode montage and the channel sets [1]

Illustration 3: The 6x6 matrix of characters. A row or column flashes for 125 ms and no flash duration is 475 ms. Scenario constructed using OpenViBE.

Illustration 4: Emotiv Epoc electrode positions


2. Results and findings

2.1. Session 1 (id h7): Comparing target epochs (60) and non-target epochs (298)

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Illustration 5: ERPs of targets

Illustration 6: ERPs of non-targets



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Discussion 1

• All three sessions 1-3 shows somewhat clear ERP waveforms for target stimuli and their peak powers are higher than for non-target peak powers.

• However, session 3 peak powers are relatively lower than in both session 1 and 2. So a question arises as is it because the number of epochs are higher in session 3, or in other words, when the number of epochs gets larger the averaged signals' peak powers get lower? Some other thing observed during session 3 is that about 5 minutes after the experiment the headset's battery gone dead. To clarify the fact, session 1 and 2 data can be combined to form a larger session and compare with session 3.

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2.4. Session 4 (id h8=h6+h7): Comparing target epochs (120) and non-target epochs (598)

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Discussion 2

• Session 4 ERPs clearly show that it is not the number of epochs which has weakened the peak powers of ERP waveforms. Therefore, it is safe to assume that the weakening of signal strengths has caused by the battery.

• On contrary, illustration 11 shows that when the number of epochs get larger, the resulting ERP waveforms get much clearer.

• Illustration 13 shows how ERPs for targets distributed over each scalp location (each 14 EEG channels). It is worth to find-out, which location(s) are most effective in capturing P300 signals.

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Illustration 13: ERP scalp array for targets


2.5. ERP images for each EEG channel for targets

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2.6. ERP images for left EEG channel locations for non-targets

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Discussion 3

• From the ERP images for targets for each EEG channel locations, P300 response is somewhat more clearer at locations P7 and O1, and less clearer at locations P8, O2, FC5, FC6, F3 and F4. No ERP like waveform is visible at other locations.

• Non-target ERP images show that for non-targets there is no identifiable ERP images.

Conclusion

Emotiv EPOC does capture actual EEG and the noise can be minimized using techniques like averaging. However, EEG signals captured by Emotiv EPOC is not good as professional/clinical type of EEG system. Another problem is that Emotiv headset does not cover some important locations in the scalp. From the analysis it can be seen that P7 and O1 locations are good in obtaining P300 responses. Someone can further study how this process can be improved, such as by using ICA.

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Part 2: Experiment framework and tools

1. Overall architecture

System and tools:• Dell Latitude E6400 laptop• Windows Vista• Emotiv Epoc research edition• Emotiv TestBench v1.5• OpenViBE v0.8.0• com0com null modem emulator• PortWrite serial port writer• Matlab and EEGLAB toolbox for off-line analysis

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Scenario in OpenViBE runs the experiment

TestBench records EEG data and events

com0com

Markers to TestBench via serial

port


2. OpenViBE scenario

Resources:• The OpenViBE scenario (p300-experiment-scenario.xml)• File for XML stimulation scenario player (same as one in the OpenViBE installation) Note:

change the path to the file p300-speller-stimulations-targets.xml• Configure PATH variable under Windows environment variables to include the folder

containing PortWrite.exe

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Generates all thestimulations (events)for the experiment

Keyboard eventto start theexperiment

Generates randomtargets

Shows the grid andintensity according to

stimulation

Send markers toserial port


3. The process of P300 Speller Stimulator (Approximated)

Note that the dashed lines represent the stimulations (events) issued by the component.

Blog place:

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Sequence of 12 stimuli (segments); flash duration 125 ms; no-flash duration 475 ms

Repetitions > 0 ?

Repetitions = Repetitions-1

Trials = 6Inter-trial delay = 5000 ms

Inter-repetition delay = 600 ms

Experiment start

Inter-trial delay

Inter-repetition delay

Trials = Trials-1

Trials != 0 ?

Yes No

Yes

Experiment stopNo

Repetitions = 5

ExperimentStart

ExperimentStopRestStart

RestStop

TrialStart

TrialStopSegmentStart SegmentStop

(Label Id; VisualStimulationStart; VisualStimulationStop) x 12


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References

[1] Krusienski, D.J., Sellers, E.W., McFarland, D.J., Vaughan, T.M., Wolpaw, J.R. (2008). Toward enhanced P300 speller performance. Journal of Neuroscience Methods,167:15-21. [2] L.A. Farwell and E. Donchin, "Talking off the top of your head: toward a mental prosthesis utilizing event-related brain potentials," Electroenceph. Clin. Neurophy., vol. 70, pp. 510-523, 1988.[3] A. T. Campbell et al., “NeuroPhone: Brain-Mobile Phone Interface Using a Wireless EEG Headset,” Proc. 2nd ACM SIGCOMM Wksp. Networking, Sys., and Apps. on Mobile Handhelds, New Delhi, India, Aug. 30, 2010.

Last edited: October 07, 2011Posted on: December 25, 2010

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