Headgear for Mobile Neurotechnology: looking into Alternatives for EEG and NIRS probes

Brain-computer interfaces are now entering real-life environments. Particular hybrid systems using more than one input signal, e.g. electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS), offer a broad spectrum of applications in basic research and clinical neuroscience. Here, we provide an overview of recent EEG-electrode and fNIRSoptode approaches that aim to improve usability. We include our new multi-function clip-on design that allows the use of conventional gel-based ring electrodes with water. For EEG electrode approaches (conventional gel, solid gel, new custom water-based) we compared impedances and frequency response over multi-hour recordings. While the water-based solutions showed comparable performance in terms of signal quality, applicability and comfort, solid-gel electrodes on hairy skin required additional contact pressure. Overall, however, all tested EEG electrode types were well compatible with concurrent fNIRS recordings using a novel hybrid fNIRS/EEG headgear, paving the way for cognitive workload experiments under real-life conditions.