Abstract
Recent advances in electroencephalographic (EEG) acquisition allow for recordings using wet and dry sensors during whole-body motion. The large variety of commercially available EEG systems contrasts with the lack of established methods for objectively describing their performance during whole-body motion. Therefore, the aim of this study was to introduce methods for benchmarking the suitability of new EEG technologies for that context. Subjects performed an auditory oddball task using three different EEG systems (Biosemi wet—BSM, Cognionics Wet—Cwet, Conionics Dry—Cdry). Nine subjects performed the oddball task while seated and walking on a treadmill. We calculated EEG epoch rejection rate, pre-stimulus noise (PSN), signal-to-noise ratio (SNR) and EEG amplitude variance across the P300 event window (CVERP) from a subset of 12 channels common to all systems. We also calculated test-retest reliability and the subject’s level of comfort while using each system. Our results showed that using the traditional 75 μV rejection threshold BSM and Cwet epoch rejection rates are ~25% and ~47% in the seated and walking conditions respectively. However, this threshold rejects ~63% of epochs for Cdry in the seated condition and excludes 100% of epochs for the majority of subjects during walking. BSM showed predominantly no statistical differences between seated and walking condition for all metrics, whereas Cwet showed increases in PSN and CVERP, as well as reduced SNR in the walking condition. Data quality from Cdry in seated conditions were predominantly inferior in comparison to the wet systems. Test-retest reliability was mostly moderate/good for these variables, especially in seated conditions. In addition, subjects felt less discomfort and were motivated for longer recording periods while using wet EEG systems in comparison to the dry system. The proposed method was successful in identifying differences across systems that are mostly caused by motion-related artifacts and usability issues. We conclude that the extraction of the selected metrics from an auditory oddball paradigm may be used as a benchmark method for testing the performance of different EEG systems in mobile conditions. Moreover dry EEG systems may need substantial improvements to meet the quality standards of wet electrodes.
Highlights
Descriptions of brain activity using non-invasive electroencephalographic (EEG) have become an important topic in recent years
Varying the amplitude of cutoff thresholds showed that a traditional threshold at 75 μV may remove ∼30% of the seated epochs for BSM and Cognionics wet (Cwet) (Figure 2B), and this same threshold may remove ∼68% of the seated epochs for Cognionics dry (Cdry)
The results revealed interaction between EEG system and condition (F(1,192) = 55.78, p < 0.001), showing that Cdry in seated condition had significantly higher CVERP in comparison to other EEG systems in the same condition (Figure 5B, data from all channels combined in the boxplots)
Summary
Descriptions of brain activity using non-invasive electroencephalographic (EEG) have become an important topic in recent years. Due to the high dynamic range and low signal-to-noise in these types of situations, acquiring reliable records of brain electrical activity in these motion conditions requires robust EEG acquisition systems beyond what has been conventionally used in more restricted laboratory or medical scenarios. Such achievement can contribute substantially to advance many research areas, such as psychology, motor rehabilitation, aging, robotics, and user-system interaction (Lance et al, 2012; McDowell et al, 2013; Kranczioch et al, 2014)
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