Event Abstract

Implementation of Synchronization Triggers in an open-source EEG system for Visual Evoked Potentials measurement

  • 1 PUCP, Faculty of Arts & Humanities, Peru
  • 2 PUCP, Engineering Department, Peru
  • 3 PUCP, Psychology Department, Peru

Introduction The increasing use of low-cost consumer-grade EEG devices in neuroscience research and brain computer interface research and development, generates the requirement to assess these systems in terms of their suitability for research purposes (Badcock et. al, 2013; Badcock et. al, 2015; Debener, Minow, Emkes, Gandras & Vos, 2012; Maskeliunas, Damasevicius, Martisius & Vasiljevas, 2016; Ries, Touryan, Vettel, McDowell & Hairston, 2014; Suryotrisongko & Samopa, 2015) . One crucial aspect for cognitive oriented electroencephalographic research is synchronization between data acquisition and stimulus presentation: It has been reported that low-cost consumer-grade EEG devices may present timing accuracy problems (Hairston, 2012; Hairston et. al, 2014) and to our knowledge, conclusive solutions to these problems have not been reported yet. Therefore, the aim of this work is to synchronize by a customized conversion circuit, the onset of a single, discrete and iterative computer monitor event and the onset of visual evoked potential signals. Methods A right-handed 21 years old male participant with no neurological or psychiatric disorders was recruited for this experiment. Verbal informed consent was given. Stimulus presentation to elicit visual evoked potentials was performed with PsychoPy2 v.1.83.04 (Peirce, 2007). A 4x4 checkerboard was employed to perform 500 reversals at a rate of 0.5 Hz. The monitor event was the change of color from white to black and from black to white of a square sector of the monitor. The square sector was located to the right and to the bottom of the monitor. The critical function of the circuit was to work as a voltage divider to acquire first a voltage depending on the color changes of the square by a photoresistor and a resistor, and then feed an operational amplifier to produce a logical voltage output to mark events in the EEG system data output (Fig. 1). Visual evoked potential signals were acquired with OpenBCI Ultracortex Mark III “Supernova” (V3 - 32-bit board) from Oz and referenced to Pz location according to the 10-20 system. The system had a sampling rate of 250 Hz, 24-bit channel resolution, dry electrodes and an ADS1299 analog to digital converter. An ear-clip electrode attached to the right earlobe was used as ground. No notch filters were applied and impedance was kept below 10KOhm. Collected EEG data was processed offline according to VEP clinical standards (Odom et. al, 2010) using EEGLAB v.13.5.4b (Delorme & Makeig, 2004). Data was epoched from 0 to 250ms after stimulus and band pass FIR filters from 1 Hz to 100Hz were employed. For artifact removal, epochs with ± 50uV were discarded. Results and Discussion Channel event related potentials results show a N135 peak and hardly distinguishable N75 and P100 peaks (Fig. 2). No clearly distinguishable peaks may be due to insufficient sampling rate, which according to clinical standards should be at least 500Hz (Odom et. al, 2010). However, these results provide initial evidence that the implemented synchronization triggers may be used as a simple and elegant solution for measuring visual evoked potential with the OpenBCI EEG system. Further research should consider using a larger sampling rate within the same hardware, increase the number of participants and employ acquired signals in a BCI environment (Bashashati, Fatourechi, Ward & Birch, 2007; Gao, Wang, Gao & Hong, 2014; Wang, Gao, Hong, Jia & Gao, 2008; Yoshimura & Itakura, 2011). Additionally, a comparison between the implemented system and professional grade equipment is advised.

Figure 1
Figure 2


Badcock, N. A., Mousikou, P., Mahajan, Y., de Lissa, P., Thie, J., & McArthur, G. (2013). Validation of the Emotiv EPOC® EEG gaming system for measuring research quality auditory ERPs. PeerJ, 1, e38. doi: 10.7717/peerj.38

Badcock NA, Preece KA, de Wit B, Glenn K, Fieder N, Thie J, McArthur G. (2015)Validation of the Emotiv EPOC EEG system for research quality auditory event-related potentials in children. PeerJ 3:e907. Doi: 10.7717/peerj.907

Bashashati, A., Fatourechi, M., Ward, R. K., & Birch, G. E. (2007). A survey of signal processing algorithms in brain–computer interfaces based on electrical brain signals. Journal of Neural engineering, 4(2), R32-R57. doi: 10.1088/1741-2560/4/2/R03

Delorme, A., & Makeig, S. (2004). EEGLAB: an open source toolbox for analysis of single-trial EEG dynamics including independent component analysis. Journal of neuroscience methods, 134(1), 9-21. Doi: 10.1016/j.jneumeth.2003.10.009

Debener, S., Minow, F., Emkes, R., Gandras, K., & Vos, M. (2012). How about taking a low‐cost, small, and wireless EEG for a walk?. Psychophysiology,49(11), 1617-1621. Doi: 10.1111/j.1469-8986.2012.01471.x

Hairston, W. D. (2012). Accounting for timing drift and variability in contemporary electroencepholography (EEG) systems (Aberdeen Proving Ground, MD: US Army Research Laboratory) Report ARL-TR-5945.

Hairston, W. D., Whitaker, K. W., Ries, A. J., Vettel, J. M., Bradford, J. C., Kerick, S. E., & McDowell, K. (2014). Usability of four commercially-oriented EEG systems. Journal of neural engineering, 11(4), 046018. doi:10.1088/1741-2560/11/4/046018

Gao, S., Wang, Y., Gao, X., & Hong, B. (2014). Visual and auditory brain–computer interfaces. IEEE Transactions on Biomedical Engineering, 61(5), 1436-1447. doi: 10.1109/TBME.2014.2300164

Maskeliunas, R., Damasevicius, R., Martisius, I., & Vasiljevas, M. (2016). Consumer-grade EEG devices: are they usable for control tasks?. PeerJ, 4, e1746. Doi: 10.7717/peerj.1746

Odom, J. V., Bach, M., Brigell, M., Holder, G. E., McCulloch, D. L., & Tormene, A. P. (2010). ISCEV standard for clinical visual evoked potentials (2009 update). Documenta ophthalmologica, 120(1), 111-119. doi: 10.1007/s10633-009-9195-4

Peirce, J. W. (2007). PsychoPy—psychophysics software in Python. Journal of neuroscience methods, 162(1), 8-13. Doi: 10.1016/j.jneumeth.2006.11.017.

Ries, A. J., Touryan, J., Vettel, J., McDowell, K., & Hairston, W. D. (2014). A comparison of electroencephalography signals acquired from conventional and mobile systems. Journal of Neuroscience and Neuroengineering, 3(1), 10-20. Doi: 10.1166/jnsne.2014.1092

Suryotrisongko, H., & Samopa, F. (2015). Evaluating OpenBCI Spiderclaw V1 Headwear's Electrodes Placements for Brain-Computer Interface (BCI) Motor Imagery Application. Procedia Computer Science, 72, 398-405. doi: 10.1016/j.procs.2015.12.155

Ultracortex Mark III "Supernova" (n.d.). Retrieved June 22, 2016, from http://openbci.com/

Wang, Y., Gao, X., Hong, B., Jia, C., & Gao, S. (2008). Brain-computer interfaces based on visual evoked potentials. IEEE Engineering in medicine and biology magazine, 27(5), 64-71. doi: 10.1109/MEMB.2008.923958

Yoshimura, N., & Itakura, N. (2011). Usability of Transient VEPs in BCIs. INTECH Open Access Publisher. doi: 10.5772/14171

Keywords: EEG, Event Related Potentials (ERPs), visual evoked potential (VEP), open source implementation, Syncrhonization

Conference: SAN2016 Meeting, Corfu, Greece, 6 Oct - 9 Oct, 2016.

Presentation Type: Oral Presentation in SAN 2016 Conference

Topic: Oral Presentations

Citation: Paredes R, Laurel C, Cuellar F and Davila A (2016). Implementation of Synchronization Triggers in an open-source EEG system for Visual Evoked Potentials measurement. Conference Abstract: SAN2016 Meeting. doi: 10.3389/conf.fnhum.2016.220.00007

Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.

The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.

Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.

For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.

Received: 29 Jul 2016; Published Online: 30 Jul 2016.

* Correspondence: Mr. Renato Paredes, PUCP, Faculty of Arts & Humanities, Lima, Lima, Lima 32, Peru, renato.paredes@pucp.edu.pe