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

Renato Paredes1*, Christihan Laurel2, Francisco Cuellar2 and Alex Davila3
  • 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.

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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

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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