刺激视野面积对稳态视觉诱发电位的影响

基于稳态视觉诱发电位（SSVEP）的脑-机接口（BCI）系统通常采用占据较大视野面积的闪烁刺激以诱发更明显的脑电特征,但容易造成使用者疲劳、紧张和头痛,限制了SSVEP-BCI的实际应用。针对此问题,该文以幅值、信噪比、典型相关系数和任务相关系数为指标,探究了不同刺激视野面积（以角度尺寸进行衡量,范围为0.1°至13°）对诱发SSVEP信号特征强度的影响。分析结果表明,SSVEP信号的强度最初随刺激角度尺寸的增大而增大,但在角度尺寸达到3°左右后增长开始变缓并保持平稳。综合考虑系统舒适度和特征强度两个因素后得出结论,SSVEP-BCI系统的刺激角度尺寸约为3°时能够达到最佳性能。该文为SSVEP-BCI的最佳刺激角度尺寸选择提供了依据,相关研究成果在舒适友好型BCI方面具有潜在的应用价值。      

不同占空比光刺激对稳态视觉诱发电位的影响研究

目前稳态视觉诱发电位(Steady-State Visual Evoked Potentials, SSVEP)被广泛应用于脑机接口技术和医学临床检测和治疗.了解影响SSVEP参数及其规律非常必要.针对目前不同学者在不同实验条件下测试闪烁光脉冲占空比对SSVEP影响的结果差异较大而难以归纳其共性规律问题, 将光脉冲刺激下产生神经冲动的视觉皮层细胞沿内外膜流动的电流等效为一磁偶极子, 在此基础上建立了人头部空间电场及SSVEP计算模型.采用该模型对光脉冲占空比影响SSVEP的规律进行了分析, 并开展了相关实验.研究结果表明:在闪烁光频率和强度相同条件下, 光脉冲占空比对SSVEP各次谐波振幅及其平均功率的影响呈现多“窗口”效应.实验数据与理论研究结果一致.     

面向中高频SSVEP脑机接口的编解码算法研究

基于稳态视觉诱发电位（steady-state visual evoked potentials,SSVEPs）的脑-机接口系统（brain-computer interface,BCI）通常使用低频强闪烁刺激诱发强特征脑电信号。尽管相关数据处理技术日臻成熟,但是系统使用舒适度差,训练时间较长。提高刺激频率能够有效缓解受试者的视觉疲劳,提高系统友好度,然而现有中高频SSVEP系统又存在指令集数量少、信息传输率（information transfer rate,ITR）低等缺陷。针对以上问题,本文基于中高频SSVEP脑电特征,提出并使用了包含空码的Code Words编码范式与集成任务相关成分分析（ensemble task-related component analysis, eTRCA）解码算法,并研究了该套编解码方法的适用性与可扩展性。本研究选择中高频段的4个频率（20、24、30、40 Hz）分别构建脑控字符拼写系统,单个频率的闪烁刺激可独立构建多达6个控制指令,联合多个频率理论上可实现指令集数量的成倍扩增。共有10位健康受试者参与了离线脑电实验,利用18~60 Hz带通滤波对脑电数据进行预处理,使用eTRCA算法进行特征识别。18指令集系统的理论平均分类准确率为96.71±1.69 %,理论平均ITR达86.94±6.07 bits/min。以上结果表明,本研究提出的编解码算法能够有效诱发并准确识别中高频SSVEP的时-频-相多维特征,在此基础上通过增加编码单元频率种类、提高有效编码率、改进解码算法等方式有希望进一步提升系统性能。      

基于LED电流、温度光谱模型的照明系统研究

电流、温度的改变都会影响LED光谱分布,从而影响光源的视觉和非视觉参数。文中从基于LED芯片发光材料中光子能级分布规律的光谱模型出发,对RGBY四色LED建立电流、温度模型,拟合的R-square可达到0.99。在此基础上,通过遗传算法对昼夜节律因子和辐射发光效率进行多目标优化,在照度为300 lx时,设计8组兼顾视觉参数（显色指数和蓝光危害效率）以及非视觉参数（昼夜节律刺激）的照明方案,通过这些方案验证了该模型的可行性。接着,探究两种非视觉参数和温度的关系,结果表明昼夜节律因子均随温度的增加而升高,但昼夜节律刺激却随温度的增加而减小。这种情况的原因是两种参数受照度的影响不同,对照度补偿后,发现两种非视觉参数均随温度的升高而增大,二者呈现一定的正相关性。该研究从光源光谱的角度入手,为LED照明光源设计中非视觉效应的考量提供参考依据。     

基于单片机和Android系统的智能LED光闪烁系统的设计和实现

神经科学领域利用一定频率的闪光刺激调控阿尔茨海默病(AD)模型动物的Aβ淀粉样蛋白沉积。因此,频率可调的LED光源在AD的发病机制和神经调控中有很好的应用。文中根据频率可调的需求,设计基于Android的频率可调LED光源。使用Android客户端,通过蓝牙模块与底层MCU SRC89C52进行通信,底层MCU负责执行命令,控制LED驱动电路的开关,实现LED的频率可调控制。实验结果表明,该装置具有成本低、操作简单等特点。     

LED引线键合机中的双光路成像系统

引线键合机是半导体后封装设备中的关键技术产品,LED芯片和引脚的高度差较大,表面反光特性不同,一组镜头和光源很难获得清晰的图像,为了满足图像识别的需要,设计了一种适用于LED全自动引线键合机的双光路成像系统。识别芯片和引脚时通过一个电子切换装置自动切换到不同倍率,并配合光源的变化,大大提高了视觉系统的精确性。     

荧光粉预沉淀对COB白光LED光色参数的影响

制作了高光效高显指COB封装LED光源,研究了点涂荧光胶后光通量、色坐标、光谱等光色参数随荧光粉预沉淀时间的变化关系。研究结果表明,在预沉淀初期(约5min),LED光源光色参数随预沉淀时间变化较大,之后进入一个缓慢变化的阶段。研究认为这一现象的出现是因为粒径不同的荧光粉颗粒沉淀速度不同造成的,预沉淀初期,大粒径的荧光粉颗粒迅速沉淀,造成LED光源光色参数剧烈变化,之后小粒径的荧光粉缓慢沉淀,LED光源光色参数也呈现缓慢变化的趋势。在实际生产中,将预沉淀时间控制在15～25min,取得了良好的效果,主货率(颜色在一个档位的比例)达到98%以上。     

MSI和CCA算法对稳态视觉诱发电位信号分类的比较研究

脑机接口（Brain Computer Interface, BCI）系统能让那些有运动障碍的病人用脑信号与外界设备交互。稳态视觉诱发电位（Steady State Visual Evoked Potential,SSVEP）具有分析正确率高,不用训练等优点而倍受重视。如何高效地对SSVEP信号频率识别是SSVEP-BCI的关键问题,并关系到BCI的系统优劣。本文采用多变量同步指数与典型相关分析方法对SSVEP信号分类进行比较研究,探讨了两种方法在数据长度、导联数量、导联位置以及参考信号的谐波数量对SSVEP信号分类效果的影响。六位被试者参与实验采集数据,实验结果证实,在时间窗较小,数据长度较少的条件下,多变量同步指数方法较典型相关分析方法性能更优。而对于SSVEP信号分析来说,导联位置的准确性是影响频率分析算法的最根本因素。      

基于双谱的稳态视觉诱发电位脑机接口导联选择算法

基于稳态视觉诱发电位(SSVEP)的脑机接口中,识别算法所用的导联通常是固定的.然而,被试间存在个体性差异,针对不同被试使用个性化导联组合有助于提升算法识别SSVEP的性能.本文提出了一种基于双谱的导联选择算法,它利用SSVEP双谱和参考信号双谱之间的欧氏距离作为度量指标,对所有导联进行排序,并使用模糊系统融合SSVEP产生区域的先验知识,自主决定是否使用个性化导联.实验结果表明,被试使用本算法选择的个性化导联组合能够实现更高的SSVEP分类准确率和信息传输速率.     

基于稳态视觉诱发电位的脑机接口元素尺寸和间距工效学研究

针对基于稳态视觉诱发电位(SSVEP)的脑机接口系统,该文开展了屏显刺激界面元素尺寸和间距对识别效率和用户体验影响的工效学实验研究.该工效学实验使用红色正方形作为频闪刺激元素,刺激元素位于上、下、左、右等4个位置,自变量包含尺寸和间距两个因素.因素1为尺寸即正方形边长,分为100px,150px,200px3个水平;因...     

An SSVEP-based BCI using high duty-cycle visual flicker

Steady-state visual-evoked potential (SSVEP)-based brain-computer interfaces (BCIs) have generated significant interest due to their high information transfer rate (ITR). Due to the amplitude-frequency characteristic of the SSVEP, the flickering frequency of an SSVEP-based BCI is typically lower than 20 Hz to achieve a high SNR. However, a visual flicker with a flashing frequency below the critical flicker-fusion frequency often makes subjects feel flicker jerky and causes visual discomfort. This study presents a novel technique using high duty-cycle visual flicker to decrease user's visual discomfort. The proposed design uses LEDs flashing at 13.16 Hz, driven by flickering sequences consisting of repetitive stimulus cycles with a duration T (T = 76 ms). Each stimulus cycle included an ON state with a duration T(ON) and an OFF state with a duration T(OFF) (T = T(ON) + T(OFF)), and the duty cycle, defined as T(ON)/T, varied from 10.5% to 89.5%. This study also includes a questionnaire survey and analyzes the SSVEPs induced by different duty-cycle flickers. An 89.5% duty-cycle flicker, reported as a comfortable flicker, was adopted in a phase-tagged SSVEP system. Six subjects were asked to sequentially input a sequence of cursor commands with the 25.08-bits/min ITR.     

Complex-Valued Spatial Filters for SSVEP-Based BCIs With Phase Coding

Brain-computer interface (BCI) systems based on steady-state visual evoked potentials (SSVEPs) have gained considerable popularity because of the robustness and high information transfer rate these can provide. Typical SSVEP setups make use of visual targets flashing at different frequencies, where a user's choice is determined from the SSVEPs elicited by the user gazing at a specific target. The range of stimulus frequencies available for such setups is limited by a variety of factors, including the strength of the evoked potentials as well as user comfort and safety with light stimuli flashing at those frequencies. One way to tackle this limitation is by introducing targets flickering at the same frequency but with different phases. In this paper, we propose the use of the analytic common spatial patterns (ACSPs) method to discriminate between phase coded SSVEP targets, and we demonstrate that the complex-valued spatial filters used for discrimination can exceed the performance of existing techniques. Furthermore, the ACSP method also yields a set of spatial patterns, separable into amplitude and phase components, that provide insight into the underlying brain activity.     

天幕靶人工光源的设计

针对天幕靶在使用时必须有非常稳定的光源,为了实现天幕靶能够全天候测量以及在室内测量,设计采用LED作为天幕靶的人工光源;分析了LED的特性,提出用超高亮度平头发光二极管作为人工光源,通过器材设计半径为5m的扇形形状LED光源。采用恒压供电,经过试验,该光源满足天幕靶在阴天或室内光线比较暗时测速的要求,而且对天幕靶的灵敏度有大幅度的提高。     

室内照明用白光LED光源照度对人眼视网膜的影响研究

针对白光LED光源对视功能影响进行医学实验研究,对不同照度下的各组大鼠视网膜电图进行检测,并比较不同光源照度对典型视网膜电图数据特征指标的影响.相对于正常对照组,300 lux照度的白光LED光源照射下,大鼠视网膜电图数据基本无异常,个别特征出现差异趋势;1 000 lux照度的白光LED光源照射下,鼠视网膜电图数据异常,个别特征出现明显差异,因此,可以初步确定白光LED光源的安全阈值照度为300 lux,LED光源照射下视网膜安全性的实验研究将为其进入室内照明应用提供理论基础.     

Accounting for phase drifts in SSVEP-based BCIs by means of biphasic stimulation

This study proposes a novel biphasic stimulation technique to solve the issue of phase drifts in steady-state visual evoked potential (SSVEPs) in phase-tagged systems. Phase calibration was embedded in stimulus sequences using a biphasic flicker, which is driven by a sequence with alternating reference and phase-shift states. Nine subjects were recruited to participate in off-line and online tests. Signals were bandpass filtered and segmented by trigger signals into reference and phase-shift epochs. Frequency components of SSVEP in the reference and phase-shift epochs were extracted using the Fourier method with a 50% overlapped sliding window. The real and imaginary parts of the SSVEP frequency components were organized into complex vectors in each epoch. Hotelling's t-square test was used to determine the significances of nonzero mean vectors. The rejection of noisy data segments and the validation of gaze detections were made based on p values. The phase difference between the valid mean vectors of reference and phase-shift epochs was used to identify user's gazed targets in this system. Data showed an average information transfer rate of 44.55 and 38.21 bits/min in off-line and online tests, respectively.     

视觉检测系统LED光源照度优化方法

针对当前视觉检测系统LED光源照度优化研究中存在的照度效果评价因素单一、照度优化方法通用性不足等问题,以芯片封装质量视觉检测为例,提出一种基于改进樽海鞘算法的LED光源照度优化方法。该方法在单个LED光源照度数学模型基础上,建立标准条形LED阵列光源照度数学模型,获取条形LED阵列在任意空间位姿与被测面的照度值;基于照度均匀度、照度梯度变化与对中度、平均照度、目标与背景区分度等因素建立平面照度效果评价函数;提出改进樽海鞘算法,通过改进算法收敛系数、速度、领导者与追随者位置等更新策略,增强区域搜索的多样性;应用改进樽海鞘算法对平面照度效果评价函数进行优化求解,获取具有最优照度效果的空间位姿参数。实验结果表明:考察优化区域的相对照度分布,文中提出的LED光源照度优化方法所得照度分布与实际测量所得照度分布结果基本一致,目标区域理论照度均匀度在98.78%以上,误差在5.57%以内。因此文中提出方法优化目标合理,可用于视觉检测系统具有最优照度效果时光源位姿信息参数的获取。     

Effects of Saccade Length and Target Luminance on the Refresh Frequency Threshold for the Visibility of Color Break-Up

Field-sequential color displays are susceptible to a visual artefact called color break-up, which is an image-quality problem and may also cause visual discomfort. However, the effect can be greatly reduced by increasing the refresh frequency of the display. In this study, we measured refresh frequency thresholds for color break-up visibility by using a two-alternative forced choice staircase method. Subjects made controlled horizontal saccades so that the gaze followed a white target which abruptly changed position. The white target was a red, green, and blue (RGB) light-emitting diode (LED), in which the red, green, and blue colors were shown sequentially. Saccade length (2, 4, 8, and 14 deg) and target luminance level (2, 31.5, and 500 cd/m) were varied. The contrast between stimulus and background and the size of the stimulus were held constant. The results showed that a refresh frequency as high as 1200 Hz would be needed to completely eliminate the phenomenon. Further, the threshold value increased with saccade length and target luminance. However, the effect of luminance saturated relatively early.