Multi‐command SSAEP‐based BCI system with training sessions for SSVEP during an eye fatigue state

This paper proposes a steady‐state auditory stimulus modality and a detection algorithm to replace steady‐state visual evoked potential (SSVEP )‐based brain–computer interface (BCI ) systems during visual fatigue periods. The optimal speaker position for the steady‐state auditory evoked potential (SSAEP )‐based BCI system and possible electrode positions are investigated. Using the proposed system, an accuracy of 85% for two commands was achieved based on the T3–T5 and T4–T6 electrode positions using only one speaker. SSAEP is a promising BCI modality for mitigating the problem of eye fatigue that often occurs during the use of SSVEP ‐based BCI systems. However, SSAEP ‐based BCI systems suffer from low accuracy. To increase accuracy, we propose a new enhanced SSAEP training method. The training process was enhanced by instructing users to control their attention levels while simultaneously detecting an auditory stimulus frequency. Furthermore, we propose a corresponding single‐frequency, multi‐command BCI paradigm for the proposed training method. With the proposed paradigm, four commands can be detected using only one auditory stimulus frequency. The proposed training system yielded an accuracy of ∼81% compared to 66% for sessions performed without the proposed training method. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

结合表面肌电与稳态视觉诱发电位的混合脑机接口关键技术研究

脑-机接口技术旨在大脑与外部环境之间建立一种全新的不依赖于外周神经和肌肉的交流与控制通道。基于稳态视觉诱发电位的脑-机接口是目前信息传输率最高的无创脑 机接口范式，但是仍低于传统的交互方式。提出一种结合表面肌电与稳态视觉诱发电位的混合脑 机接口，以进一步提高系统的信息传输率。通过不同频率的高频稳态视觉诱发电位结合sEMG编码，实现二者混合脑 机接口系统。利用典型相关分析方法对SSVEP信号进行频率识别，sEMG的检测则采用频域分析方法。来自8名健康受试者的离线结果表明该系统能够获得8428% 的平均准确率，平均信息传输率为7263 bits/min。这些结果为结合表面肌电与稳态视觉诱发电位的混合脑 机接口研究奠定了基础。     

Image‐based visual target following for a nonholonomic wheeled mobile robot with a single fixed camera

This paper addresses the problem of visual target following for a nonholonomic wheeled mobile robot with a single fixed camera. For the problem, we propose a control scheme composed of vision‐based trajectory planning and tracking control. We present online trajectory planning based on image‐based visual servoing. The key idea is to compensate the target object motion. In particular, we focus on visual feature motion resulting from the target object motion. Tracking control to the generated trajectory can therefore achieve visual target following precisely even if the target object is moving. Our proposed scheme can be applied to, e.g. robotic systems for autonomous guard and observation. The effectiveness of the control system is evaluated experimentally. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

视觉通路下闪光刺激对SSVEP影响的仿真研究

稳态视觉诱发电位(steady-state visual evoked potentials,SSVEP)是一种在频率固定的重复视觉刺激下出现的大脑皮层稳态响应。针对目前不同学者在不同实验条件下测试闪光刺激的参数(占空比、频率)对SSVEP影响结果差异较大而难以归纳其共性规律问题,本文基于集总参数模型法,将光刺激下视觉通路的同一类神经元等效为一个单元,利用单元间的耦合系数建立视觉通路计算模型,并通过该模型仿真研究闪光刺激的占空比和频率对SSVEP影响的初步规律,为刺激参数的选择提供有价值的理论依据。最后通过实验验证了模型的可靠性及结论的有效性。     

A wavelet‐based piecewise approach for steady‐state analysis of power electronics circuits

Simulation of steady‐state waveforms is important to the design of power electronics circuits, as it reveals the maximum voltage and current stresses being imposed upon specific devices and components. This paper proposes an improved approach to finding steady‐state waveforms of power electronics circuits based on wavelet approximation. The proposed method exploits the time‐domain piecewise property of power electronics circuits in order to improve the accuracy and computational efficiency. Instead of applying one wavelet approximation to the whole period, several wavelet approximations are applied in a piecewise manner to fit the entire waveform. This wavelet‐based piecewise approximation approach can provide very accurate and efficient solution, with much less number of wavelet terms, for approximating steady‐state waveforms of power electronics circuits. Copyright © 2006 John Wiley & Sons, Ltd.     

Adaptive harmonic steady‐state control for rejection of sinusoidal disturbances acting on a completely unknown system

This paper presents an adaptive harmonic steady‐state (AHSS) controller that addresses the problem of rejecting sinusoids with known frequencies that act on a completely unknown asymptotically stable linear time‐invariant system. We analyze the stability and closed‐loop performance of AHSS for multi‐input multi‐output systems that are square (ie, the number of controls equals the number of performance measurements). In this case, we show that AHSS asymptotically rejects disturbances, that is, the performance measurement tends to 0. We also present a numerical study of the steady‐state and transient performance of AHSS for square and nonsquare systems.     

听觉刺激对稳态视觉诱发电位影响研究

基于稳态视觉诱发电位(steady state visual evoked potential,SSVEP)和听觉脑机接口技术目前已成为研究重点.未来的挑战是研究基于视觉和听觉联合统一系统框架的脑机接口技术.多感觉在不同脑区间存在的跨膜整合以及视听双刺激的交互作用,给该技术研究带来较大困难,故研究听觉刺激对枕区SSVEP影响很有意义.在闪光刺激频率为12 Hz,占空比分别为5％、20％、30％、40％、50％、60％、70％、80％、95％条件下,分别加入500、1 000、1 500 Hz的正弦纯音、响度为50 dB的听觉刺激,研究听觉对SSVEP的变化规律.结果表明,对同一受试者,视听双刺激条件下SSVEP随占空比变化依然呈现“窗口”效应,听觉刺激对SSVEP影响起增强或抑制作用.此外听觉刺激对SSVEP影响出现的占空比“窗口”的位置、数量以及对SSVEP增强或抑制作用的程度也因人而已.结果为更好研究视听相互作用机理及其在脑机接口技术应用提供有意义的实验依据.     

Brain-computer interfaces for 1-D and 2-D cursor control: designs using volitional control of the EEG spectrum or steady-state visual evoked potentials.

We have developed and tested two electroencephalogram (EEG)-based brain-computer interfaces (BCI) for users to control a cursor on a computer display. Our system uses an adaptive algorithm, based on kernel partial least squares classification (KPLS), to associate patterns in multichannel EEG frequency spectra with cursor controls. Our first BCI, Target Practice, is a system for one-dimensional device control, in which participants use biofeedback to learn voluntary control of their EEG spectra. Target Practice uses a KPLS classifier to map power spectra of 62-electrode EEG signals to rightward or leftward position of a moving cursor on a computer display. Three subjects learned to control motion of a cursor on a video display in multiple blocks of 60 trials over periods of up to six weeks. The best subject's average skill in correct selection of the cursor direction grew from 58% to 88% after 13 training sessions. Target Practice also implements online control of two artifact sources: 1) removal of ocular artifact by linear subtraction of wavelet-smoothed vertical and horizontal electrooculograms (EOG) signals, 2) control of muscle artifact by inhibition of BCI training during periods of relatively high power in the 40-64 Hz band. The second BCI, Think Pointer, is a system for two-dimensional cursor control. Steady-state visual evoked potentials (SSVEP) are triggered by four flickering checkerboard stimuli located in narrow strips at each edge of the display. The user attends to one of the four beacons to initiate motion in the desired direction. The SSVEP signals are recorded from 12 electrodes located over the occipital region. A KPLS classifier is individually calibrated to map multichannel frequency bands of the SSVEP signals to right-left or up-down motion of a cursor on a computer display. The display stops moving when the user attends to a central fixation point. As for Target Practice, Think Pointer also implements wavelet-based online removal of ocular artifact; however, in Think Pointer muscle artifact is controlled via adaptive normalization of the SSVEP. Training of the classifier requires about 3 min. We have tested our system in real-time operation in three human subjects. Across subjects and sessions, control accuracy ranged from 80% to 100% correct with lags of 1-5 s for movement initiation and turning. We have also developed a realistic demonstration of our system for control of a moving map display (http://ti.arc.nasa.gov/).     

Visual spatial attention tracking using high-density SSVEP data for independent brain-computer communication.

The steady-state visual evoked potential (SSVEP) has been employed successfully in brain-computer interface (BCI) research, but its use in a design entirely independent of eye movement has until recently not been reported. This paper presents strong evidence suggesting that the SSVEP can be used as an electrophysiological correlate of visual spatial attention that may be harnessed on its own or in conjunction with other correlates to achieve control in an independent BCI. In this study, 64-channel electroencephalography data were recorded from subjects who covertly attended to one of two bilateral flicker stimuli with superimposed letter sequences. Offline classification of left/right spatial attention was attempted by extracting SSVEPs at optimal channels selected for each subject on the basis of the scalp distribution of SSVEP magnitudes. This yielded an average accuracy of approximately 71% across ten subjects (highest 86%) comparable across two separate cases in which flicker frequencies were set within and outside the alpha range respectively. Further, combining SSVEP features with attention-dependent parieto-occipital alpha band modulations resulted in an average accuracy of 79% (highest 87%).     

Fixed‐point steady‐state analysis of adaptive filters

The steady‐state performance of adaptive filters can vary significantly when they are implemented in finite precision arithmetic, which makes it vital to analyse their performance in a quantized environment. Such analyses can become difficult for adaptive algorithms with non‐linear update equations. This paper develops a feedback and energy‐conservation approach to the steady‐state analysis of quantized adaptive algorithms that bypasses some of the difficulties encountered by traditional approaches. Copyright © 2003 John Wiley & Sons, Ltd.     

Studies on steady‐state stability of looped power systems and stabilization by SMES

With the increasing number of dispersed power sources interconnected to the power supply system, power systems can take a form similar to that of a longitudinal system. Also, they can become looped, with both ends of the longitudinal system connected to each other. In the present paper, the steady‐state stability of longitudinal power systems and looped power systems is analyzed by means of the mode analysis method via eigenvalue and eigenvector calculation, and power system stabilization by SMES (Superconducting Magnetic Energy Storage) for looped systems is examined relative to that for longitudinal systems. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 48–54, 2000     

Time domain and steady‐state sensitivity of periodic switched networks to element changes

Switched periodic networks are widely used in power engineering and sensitivities of their steady‐state to element changes are of interest to the designers. The paper develops a method to obtain steady‐state sensitivities for networks in which semiconductor and other switching devices are modelled as ideal short circuits without additional elements. Such modelling has the advantage that switching transients need not be calculated and correct initial conditions after switching are obtained with only four integration steps. It is also shown that sensitivities need not be calculated during the process of reaching the steady‐state. Once the steady‐state is available, integration over two additional periods is sufficient to provide time domain steady state sensitivity to the element changes. Copyright © 1999 John Wiley & Sons, Ltd.     

Independence of amplitude-frequency and phase calibrations in an SSVEP-based BCI using stepping delay flickering sequences

This study proposes a steady-state visual evoked potential (SSVEP)-based brain-computer interface (BCI) independent of amplitude-frequency and phase calibrations. Six stepping delay flickering sequences (SDFSs) at 32-Hz flickering frequency were used to implement a six-command BCI system. EEG signals recorded from Oz position were first filtered within 29-35 Hz, segmented based on trigger events of SDFSs to obtain SDFS epochs, and then stored separately in epoch registers. An epoch-average process suppressed the inter-SDFS interference. For each detection point, the latest six SDFS epochs in each epoch register were averaged and the normalized power of averaged responses was calculated. The visual target that induced the maximum normalized power was identified as the visual target. Eight subjects were recruited in this study. All subjects were requested to produce the "563241" command sequence four times. The averaged accuracy, command transfer interval, and information transfer rate (mean ± std.) values for all eight subjects were 97.38 ± 5.97%, 3.56 ± 0.68 s, and 42.46 ± 11.17 bits/min, respectively. The proposed system requires no calibration in either the amplitude-frequency characteristic or the reference phase of SSVEP which may provide an efficient and reliable channel for the neuromuscular disabled to communicate with external environments.     

A new hybrid state estimation based on pseudo‐voltage measurements

This paper presents a new hybrid state estimation method based on the concept of pseudo‐voltage measurements for a power system containing both conventional and synchronizing phasor measurements. Actual measurement data is employed to calculate the magnitude and phase of the pseudo‐voltage. In the proposed formulation, the measurement matrix describing the relations between the measured data and the state variables contains only 0 or 1. Then the state estimation problem is formulated based on the weighted least‐squares criterion, and its solution can be obtained without using iterative procedures. Comparisons with previous hybrid state estimation methods have been performed on IEEE 14‐bus, 57‐bus, and 118‐bus systems. Numerical experimental results indicate that the proposed approach yields solutions of comparable accuracy with other methods but with shorter computation times. Moreover, the proposed method also provides superior results in the presence of bad data. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于Hilbert Huang变换的SSVEP相位提取

稳态视觉诱发电位(steady-state visual evoked potential,SSVEP)被广泛应用于脑-机接口和大脑的认知研究,相位信息是其重要的特征指标之一.针对快速傅里叶变换在SSVEP相位提取中受不确定性原理约束的特点,提出了一种基于Hilbert-Huang变换的SSVEP相位提取方法.该方法通过经验模态分解将脑电信号分解为一系列固有模态函数(intrinsic mode functions,IMF),并通过分析各模态函数瞬时频率的均值判断该IMF分量是否属于噪声.若为噪声则将其从原始信号中滤除,再对滤波后的各IMF分量进行Hilbert变换,并与基准信号做运算即可求得SSVEP相位.实验结果表明,与快速傅里叶法相比该方法可在去除噪声分量的同时提取SSVEP的相位信息,且具有较高的准确率、精度和自适应性.     

Dry and noncontact EEG sensors for mobile brain-computer interfaces

Dry and noncontact electroencephalographic (EEG) electrodes, which do not require gel or even direct scalp coupling, have been considered as an enabler of practical, real-world, brain-computer interface (BCI) platforms. This study compares wet electrodes to dry and through hair, noncontact electrodes within a steady state visual evoked potential (SSVEP) BCI paradigm. The construction of a dry contact electrode, featuring fingered contact posts and active buffering circuitry is presented. Additionally, the development of a new, noncontact, capacitive electrode that utilizes a custom integrated, high-impedance analog front-end is introduced. Offline tests on 10 subjects characterize the signal quality from the different electrodes and demonstrate that acquisition of small amplitude, SSVEP signals is possible, even through hair using the new integrated noncontact sensor. Online BCI experiments demonstrate that the information transfer rate (ITR) with the dry electrodes is comparable to that of wet electrodes, completely without the need for gel or other conductive media. In addition, data from the noncontact electrode, operating on the top of hair, show a maximum ITR in excess of 19 bits/min at 100% accuracy (versus 29.2 bits/min for wet electrodes and 34.4 bits/min for dry electrodes), a level that has never been demonstrated before. The results of these experiments show that both dry and noncontact electrodes, with further development, may become a viable tool for both future mobile BCI and general EEG applications.     

基于Resinv-Unet的图像特征点检测方法

针对传统特征点检测算法需人为制定检测机制和基于深度学习的特征点检测网络泛化能力不强的问题,引入灰度不变量和残差结构,设计并实现具备像素级特征点检测能力的残差不变量神经网络(residual-invariant neural network, Resinv-Unet)。采用自标注的方式,在真实场景图像数据集的基础上构建用于训练神经网络的数据集。实验结果表明,Resinv-Unet相较于现有的特征点检测算法和特征点检测网络,在真实场景图像上具有更强的泛化能力和鲁棒性,在平均精确度、精确度和召回率上均取得更好的性能指标,其中,平均精确度达到0.715 5、精确度达到0.776 2、召回率达到0.713 7。     

Parallel processing of steady‐state analysis for a power electronic system by PVM3

It is important to get a steady‐state operation of a power electronic circuit for its design. The shooting method, which is one of the steady‐state analysis methods, solves a boundary value condition which equates initial values to final values after one‐period transient. This paper proposes how to process the analysis in parallel by using a Parallel Virtual Machine (PVM3) system. In particular, the multiple shooting method (MSM) which divides the shooting time into subsections is suitable because it can parallel numerical processes for the divided shooting times by using multiple CPU units independently. This parallel method is applied to converter examples which are processes by PVM3. The computed results are investigated for their convergence and CPU times to check their parallel effects. According to the MSM algorithm, CPU times are reduced almost to one‐fifth by using five computer units from a PVM3 system example. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 69–76, 2001     

Calculation of steady‐state solution of parallel‐connected buck converters with active current sharing and its parameter sensitivity

In this paper, the effect of active current‐sharing control on the steady‐state operation of parallel‐connected buck converters is investigated. The system under study consists of N voltage‐mode‐controlled buck converters connected in parallel. Three kinds of active current‐sharing schemes are considered, namely, master–slave scheme with automatic master, master–slave scheme with dedicated master, and democratic scheme. Using the principle of charge balance, the mechanism of the operating point drift arising from active current sharing is examined. A general formulation of the steady‐state solution under active current sharing is derived. Moreover, detailed parameter sensitivity analysis is performed to evaluate the effect of parameters' variation on the operating point. The results from sensitivity analysis can be used to categorize parameters for facilitating practical design. Computer simulations are presented to verify the analytical results. Copyright © 2010 John Wiley & Sons, Ltd.     

Data‐driven bounded‐error fault detection

In this paper, a new data‐driven fault‐detection method is proposed. This method is based on a new nonparametric system identification approach, which constitutes the principal contribution to this work. The fault‐detection method is a parametric model‐free approach that can be applied to nonlinear systems that work at various operating points. Not only can the fault‐detection process be applied to the steady state of each operating point, but it can also be applied to the transient state resulting from a change in the operating point. In order to detect faults, the proposed method uses an interval predictor based on bounded‐error techniques. The utilization of techniques based on bounded error enables system uncertainties to be included in an explicit way. This in turn leads to the possibility of obtaining interval predictions of the behaviour of the system, which include information on the reliability of the prediction itself. In order to show the effectiveness of the fault‐detection method, two examples are presented: in the form of a simulated process (counter‐flow shell‐and‐tube heat‐exchanger system) and an example of a real application (two‐tanks system). A comparison with two fault‐detection methods has also been included. Copyright © 2013 John Wiley & Sons, Ltd.