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Choi SI, Lee JY, Lim KM, Hwang HJ. Evaluation of Real-Time Endogenous Brain-Computer Interface Developed Using Ear-Electroencephalography. Front Neurosci 2022; 16:842635. [PMID: 35401092 PMCID: PMC8987155 DOI: 10.3389/fnins.2022.842635] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 03/03/2022] [Indexed: 11/13/2022] Open
Abstract
While previous studies have demonstrated the feasibility of using ear-electroencephalography (ear-EEG) for the development of brain-computer interfaces (BCIs), most of them have been performed using exogenous paradigms in offline environments. To verify the reliable feasibility of constructing ear-EEG-based BCIs, the feasibility of using ear-EEG should be further demonstrated using another BCI paradigm, namely the endogenous paradigm, in real-time online environments. Exogenous and endogenous BCIs are to use the EEG evoked by external stimuli and induced by self-modulation, respectively. In this study, we investigated whether an endogenous ear-EEG-based BCI with reasonable performance can be implemented in online environments that mimic real-world scenarios. To this end, we used three different mental tasks, i.e., mental arithmetic, word association, and mental singing, and performed BCI experiments with fourteen subjects on three different days to investigate not only the reliability of a real-time endogenous ear-EEG-based BCI, but also its test-retest reliability. The mean online classification accuracy was almost 70%, which was equivalent to a marginal accuracy for a practical two-class BCI (70%), demonstrating the feasibility of using ear-EEG for the development of real-time endogenous BCIs, but further studies should follow to improve its performance enough to be used for practical ear-EEG-based BCI applications.
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Affiliation(s)
- Soo-In Choi
- Department of Medical IT Convergence Engineering, Kumoh National Institute of Technology, Gumi-si, South Korea
| | - Ji-Yoon Lee
- Department of Electronics and Information Engineering, Korea University, Sejong City, South Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University, Sejong City, South Korea
| | - Ki Moo Lim
- Department of Medical IT Convergence Engineering, Kumoh National Institute of Technology, Gumi-si, South Korea
- Department of IT Convergence Engineering, Kumoh National Institute of Technology, Gumi-si, South Korea
| | - Han-Jeong Hwang
- Department of Electronics and Information Engineering, Korea University, Sejong City, South Korea
- Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University, Sejong City, South Korea
- *Correspondence: Han-Jeong Hwang,
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Mandekar S, Holland A, Thielen M, Behbahani M, Melnykowycz M. Advancing towards Ubiquitous EEG, Correlation of In-Ear EEG with Forehead EEG. SENSORS 2022; 22:s22041568. [PMID: 35214468 PMCID: PMC8879675 DOI: 10.3390/s22041568] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 01/09/2022] [Accepted: 02/14/2022] [Indexed: 11/16/2022]
Abstract
Wearable EEG has gained popularity in recent years driven by promising uses outside of clinics and research. The ubiquitous application of continuous EEG requires unobtrusive form-factors that are easily acceptable by the end-users. In this progression, wearable EEG systems have been moving from full scalp to forehead and recently to the ear. The aim of this study is to demonstrate that emerging ear-EEG provides similar impedance and signal properties as established forehead EEG. EEG data using eyes-open and closed alpha paradigm were acquired from ten healthy subjects using generic earpieces fitted with three custom-made electrodes and a forehead electrode (at Fpx) after impedance analysis. Inter-subject variability in in-ear electrode impedance ranged from 20 kΩ to 25 kΩ at 10 Hz. Signal quality was comparable with an SNR of 6 for in-ear and 8 for forehead electrodes. Alpha attenuation was significant during the eyes-open condition in all in-ear electrodes, and it followed the structure of power spectral density plots of forehead electrodes, with the Pearson correlation coefficient of 0.92 between in-ear locations ELE (Left Ear Superior) and ERE (Right Ear Superior) and forehead locations, Fp1 and Fp2, respectively. The results indicate that in-ear EEG is an unobtrusive alternative in terms of impedance, signal properties and information content to established forehead EEG.
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Affiliation(s)
- Swati Mandekar
- Institute for Bioengineering, University of Applied Sciences Aachen, 52005 Aachen, Germany; (S.M.); (M.B.)
- IDUN Technologies AG, Alpenstrasse 3, 8152 Glattpark, Switzerland; (A.H.); (M.T.)
| | - Abigail Holland
- IDUN Technologies AG, Alpenstrasse 3, 8152 Glattpark, Switzerland; (A.H.); (M.T.)
| | - Moritz Thielen
- IDUN Technologies AG, Alpenstrasse 3, 8152 Glattpark, Switzerland; (A.H.); (M.T.)
| | - Mehdi Behbahani
- Institute for Bioengineering, University of Applied Sciences Aachen, 52005 Aachen, Germany; (S.M.); (M.B.)
| | - Mark Melnykowycz
- IDUN Technologies AG, Alpenstrasse 3, 8152 Glattpark, Switzerland; (A.H.); (M.T.)
- Correspondence:
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Evaluating the Influence of Chromatic and Luminance Stimuli on SSVEPs from Behind-the-Ears and Occipital Areas. SENSORS 2018; 18:s18020615. [PMID: 29462975 PMCID: PMC5855130 DOI: 10.3390/s18020615] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Revised: 02/05/2018] [Accepted: 02/14/2018] [Indexed: 01/23/2023]
Abstract
This work presents a study of chromatic and luminance stimuli in low-, medium-, and high-frequency stimulation to evoke steady-state visual evoked potential (SSVEP) in the behind-the-ears area. Twelve healthy subjects participated in this study. The electroencephalogram (EEG) was measured on occipital (Oz) and left and right temporal (TP9 and TP10) areas. The SSVEP was evaluated in terms of amplitude, signal-to-noise ratio (SNR), and detection accuracy using power spectral density analysis (PSDA), canonical correlation analysis (CCA), and temporally local multivariate synchronization index (TMSI) methods. It was found that stimuli based on suitable color and luminance elicited stronger SSVEP in the behind-the-ears area, and that the response of the SSVEP was related to the flickering frequency and the color of the stimuli. Thus, green-red stimulus elicited the highest SSVEP in medium-frequency range, and green-blue stimulus elicited the highest SSVEP in high-frequency range, reaching detection accuracy rates higher than 80%. These findings will aid in the development of more comfortable, accurate and stable BCIs with electrodes positioned on the behind-the-ears (hairless) areas.
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Kappel SL, Looney D, Mandic DP, Kidmose P. Physiological artifacts in scalp EEG and ear-EEG. Biomed Eng Online 2017; 16:103. [PMID: 28800744 PMCID: PMC5553928 DOI: 10.1186/s12938-017-0391-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2017] [Accepted: 08/04/2017] [Indexed: 11/25/2022] Open
Abstract
Background A problem inherent to recording EEG is the interference arising from noise and artifacts. While in a laboratory environment, artifacts and interference can, to a large extent, be avoided or controlled, in real-life scenarios this is a challenge. Ear-EEG is a concept where EEG is acquired from electrodes in the ear. Methods We present a characterization of physiological artifacts generated in a controlled environment for nine subjects. The influence of the artifacts was quantified in terms of the signal-to-noise ratio (SNR) deterioration of the auditory steady-state response. Alpha band modulation was also studied in an open/closed eyes paradigm. Results Artifacts related to jaw muscle contractions were present all over the scalp and in the ear, with the highest SNR deteriorations in the gamma band. The SNR deterioration for jaw artifacts were in general higher in the ear compared to the scalp. Whereas eye-blinking did not influence the SNR in the ear, it was significant for all groups of scalps electrodes in the delta and theta bands. Eye movements resulted in statistical significant SNR deterioration in both frontal, temporal and ear electrodes. Recordings of alpha band modulation showed increased power and coherence of the EEG for ear and scalp electrodes in the closed-eyes periods. Conclusions Ear-EEG is a method developed for unobtrusive and discreet recording over long periods of time and in real-life environments. This study investigated the influence of the most important types of physiological artifacts, and demonstrated that spontaneous activity, in terms of alpha band oscillations, could be recorded from the ear-EEG platform. In its present form ear-EEG was more prone to jaw related artifacts and less prone to eye-blinking artifacts compared to state-of-the-art scalp based systems.
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Affiliation(s)
- Simon L Kappel
- Department of Engineering, Aarhus University, Finlandsgade 22, 8200, Aarhus N, Denmark.
| | - David Looney
- Pindrop, 817 West Peachtree Street NW, Suite 770, 24105, Atlanta, GA, USA.,Department of Electrical and Electronic Engineering, Imperial College, London, SW7 2BT, UK
| | - Danilo P Mandic
- Department of Electrical and Electronic Engineering, Imperial College, London, SW7 2BT, UK
| | - Preben Kidmose
- Department of Engineering, Aarhus University, Finlandsgade 22, 8200, Aarhus N, Denmark
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Mikkelsen KB, Kidmose P, Hansen LK. On the Keyhole Hypothesis: High Mutual Information between Ear and Scalp EEG. Front Hum Neurosci 2017; 11:341. [PMID: 28713253 PMCID: PMC5492868 DOI: 10.3389/fnhum.2017.00341] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 06/13/2017] [Indexed: 11/25/2022] Open
Abstract
We propose and test the keyhole hypothesis—that measurements from low dimensional EEG, such as ear-EEG reflect a broadly distributed set of neural processes. We formulate the keyhole hypothesis in information theoretical terms. The experimental investigation is based on legacy data consisting of 10 subjects exposed to a battery of stimuli, including alpha-attenuation, auditory onset, and mismatch-negativity responses and a new medium-long EEG experiment involving data acquisition during 13 h. Linear models were estimated to lower bound the scalp-to-ear capacity, i.e., predicting ear-EEG data from simultaneously recorded scalp EEG. A cross-validation procedure was employed to ensure unbiased estimates. We present several pieces of evidence in support of the keyhole hypothesis: There is a high mutual information between data acquired at scalp electrodes and through the ear-EEG “keyhole,” furthermore we show that the view—represented as a linear mapping—is stable across both time and mental states. Specifically, we find that ear-EEG data can be predicted reliably from scalp EEG. We also address the reverse view, and demonstrate that large portions of the scalp EEG can be predicted from ear-EEG, with the highest predictability achieved in the temporal regions and when using ear-EEG electrodes with a common reference electrode.
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Affiliation(s)
| | - Preben Kidmose
- Department of Engineering, Aarhus UniversityAarhus, Denmark
| | - Lars K Hansen
- Section for Cognitive System, Department of Applied Mathematics and Computer Science, Technical University of DenmarkKongens Lyngby, Denmark
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Nakamura T, Goverdovsky V, Morrell MJ, Mandic DP. Automatic Sleep Monitoring Using Ear-EEG. IEEE JOURNAL OF TRANSLATIONAL ENGINEERING IN HEALTH AND MEDICINE-JTEHM 2017; 5:2800108. [PMID: 29018638 PMCID: PMC5515509 DOI: 10.1109/jtehm.2017.2702558] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Revised: 03/03/2017] [Accepted: 04/24/2017] [Indexed: 11/08/2022]
Abstract
The monitoring of sleep patterns without patient's inconvenience or involvement of a medical specialist is a clinical question of significant importance. To this end, we propose an automatic sleep stage monitoring system based on an affordable, unobtrusive, discreet, and long-term wearable in-ear sensor for recording the electroencephalogram (ear-EEG). The selected features for sleep pattern classification from a single ear-EEG channel include the spectral edge frequency and multi-scale fuzzy entropy, a structural complexity feature. In this preliminary study, the manually scored hypnograms from simultaneous scalp-EEG and ear-EEG recordings of four subjects are used as labels for two analysis scenarios: 1) classification of ear-EEG hypnogram labels from ear-EEG recordings; and 2) prediction of scalp-EEG hypnogram labels from ear-EEG recordings. We consider both 2-class and 4-class sleep scoring, with the achieved accuracies ranging from 78.5% to 95.2% for ear-EEG labels predicted from ear-EEG, and 76.8% to 91.8% for scalp-EEG labels predicted from ear-EEG. The corresponding Kappa coefficients range from 0.64 to 0.83 for Scenario 1, and indicate substantial to almost perfect agreement, while for Scenario 2 the range of 0.65-0.80 indicates substantial agreement, thus further supporting the feasibility of in-ear sensing for sleep monitoring in the community.
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Affiliation(s)
- Takashi Nakamura
- Department of Electrical and Electronic EngineeringImperial College London
| | | | - Mary J Morrell
- Sleep and Ventilation UnitNational Heart and Lung Institute, Imperial College London.,NIHR Respiratory Disease Biomedical Research UnitRoyal Brompton and Harefield NHS Foundation Trust, Imperial College London.,Imperial College London
| | - Danilo P Mandic
- Department of Electrical and Electronic EngineeringImperial College London
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Curran MT, Merrill N, Chuang J. Passthoughts authentication with low cost EarEEG. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2017; 2016:1979-1982. [PMID: 28268717 DOI: 10.1109/embc.2016.7591112] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Personal and wearable computing are moving toward smaller and more seamless devices. We explore how this trend could be mirrored in an authentication scheme based on electroencephalography (EEG) signals collected from the ear. We evaluate this model using a low cost, single-channel, consumer grade device for data collection. Using data from 12 study participants who performed a set of 5 mental tasks, we achieve a 44% reduction in half total error rate (HTER) compared with a random classifier, corresponding to a 72% authentication accuracy in within-participants analyses and a 60% reduction and 80% accuracy in between-participant analyses. Given our results and those of previous research, we conclude that earEEG shows potential as a uniquely convenient authentication method as it is integrable into devices like earbud headphones already commonly worn in the ear, and the mental gestures generating the signal are invisible to would-be eavesdroppers.
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