A High-Speed SSVEP-Based BCI Using Dry EEG Electrodes

Abstract

A high-speed steady-state visual evoked potentials (SSVEP)-based brain-computer interface (BCI) system using dry EEG electrodes was demonstrated in this study. The dry electrode was fabricated in our laboratory. It was designed as claw-like structure with a diameter of 14 mm, featuring 8 small fingers of 6 mm length and 2 mm diameter. The structure and elasticity can help the fingers pass through the hair and contact the scalp when the electrode is placed on head. The electrode was capable of recording spontaneous EEG and evoked brain activities such as SSVEP with high signal-to-noise ratio. This study implemented a twelve-class SSVEP-based BCI system with eight electrodes embedded in a headband. Subjects also completed a comfort level questionnaire with the dry electrodes. Using a preprocessing algorithm of filter bank analysis (FBA) and a classification algorithm based on task-related component analysis (TRCA), the average classification accuracy of eleven participants was 93.2% using 1-second-long SSVEPs, leading to an average information transfer rate (ITR) of 92.35 bits/min. All subjects did not report obvious discomfort with the dry electrodes. This result represented the highest communication speed in the dry-electrode based BCI systems. The proposed system could provide a comfortable user experience and a stable control method for developing practical BCIs.

Flexible Sensors—From Materials to Applications

“…Therefore one of the most important parameters for electropotential sensors is contact resistance. Flexible resistive coupled electrodes were fabricated using Ag/AgCl conductive inks [542,543], Au [539,544,545], graphene [357], CNTs [540,546], AgNPs [546], and PEDOT:PSS [340,355,356,547]. Dry electrodes based on PDMS had a contact impedance of <4 kΩ and remained stable for 5 h [548].…”

“…The sensor had an average accuracy of 70.63%. A dry electrode presenting an accuracy of 93.2% was fabricated by coating thermoplastic PU with Ag and Ag/Cl conductive inks [542]. The impedance of the dry electrodes was 1.72 kΩ at 10 Hz and, when positioned on the scalp, it recorded a value of 38.6 kΩ at 10 Hz.…”

“…In conclusion, most of the polymer and conductive ink-based electrodes have a higher contact impedance when compared to standard Ag/AgCl electrodes. Researchers have built resistively coupled electrodes that had an accuracy of 93.2% and an impedance of 1.72 kΩ at 10 Hz [542]. Flexible signal acquisition electronics for resistively coupled electrodes were able to provide amplification factors of ≈200 for electropotential signals [540].…”

“…EEG acquisition systems have been produced using flexible electronics by combining flexible, thin-film electronics with external readout electronics [205]. Flexible electronics attempt to address practical issues such as conformability of EEG electrodes to hairy and irregular skin surfaces [548], and unobtrusive and wearable ambulatory approaches have been explored such as wearable EEG sensors (Figure 17e) [542,544].…”

A Dry Electrode Cap and Its Application in a Steady-State Visual Evoked Potential-Based Brain–Computer Interface

“…Dry electrodes need no gel nor cleaning after use. It might be an ideal EEG sensor device if it had electrical characteristic as good as a wet electrode [2][3][4]. However, the electrical connection between the dry electrode and scalp is not good due to the absence of the conductive paste buffer layer.…”