A Miniaturized SSVEP Brain-Computer Interface System
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摘要: 脑机接口(Brain-Computer Interface, BCI)正从实验室走向日常应用,其发展的核心瓶颈在于如何在不依赖笨重设备和同步线缆的前提下,实现高性能的脑电采集。现有无线系统难以在同步精度与系统微型化、无硬件束缚之间取得兼顾。为此,该文研制了一种采集端微型化且无需同步线缆的稳态视觉诱发电位(Steady-State Visual Evoked Potential, SSVEP)脑机接口系统。该系统采用分布式微型节点架构,将重量仅3.7 g、体积仅为3.05 cm3的微型采集节点隐蔽佩戴于头发间。在无需专用同步硬件、仅使用少量电极、且在非屏蔽普通室内环境下,搭建了40指令的在线SSVEP解码系统。结果显示,系统达到了(95.00±2.04)%的识别准确率与(147.24±30.52) bits/min的峰值信息传输速率。该研究为开发真正可穿戴的下一代脑机接口提供了可行的系统级解决方案。Abstract:
Objective The practical deployment of brain-computer interface (BCI) systems in daily-life scenarios is constrained by the bulkiness of acquisition hardware and the tethering cables required for reliable operation. While portable systems have been developed, achieving concurrent goals of significant device compactness, complete user mobility, and high decoding performance remains a challenge. This study aims to design, implement, and validate a wearable steady-state visual evoked potential (SSVEP) BCI system. The primary goal is to realize an integrated system featuring ultra-miniaturized, concealable acquisition hardware and a stable architecture that operates without the need for synchronization cables, and to demonstrate that this approach delivers online performance comparable to conventional laboratory systems, thereby advancing the feasibility of truly wearable BCIs. Methods A system-level solution was developed, centered on a distributed architecture to achieve wearability and hardware simplification. The core of the system is an ultra-miniaturized acquisition node. Each node, functioning as an independent EEG acquisition unit, integrates a Bluetooth Low Energy (BLE) system-on-chip (CC2640R2F), a high-precision analog-to-digital converter (ADS1291), a battery, and an electrode into a single encapsulated module. Through optimized 6-layer PCB design and a stacked assembly, the module dimensions were reduced to 15.12 mm × 14.08 mm × 14.31 mm (3.05 cm3) with a weight of 3.7 g. Each node incorporates a single active electrode, and all nodes share a common reference electrode connected via a thin, short wire. This design reduces scalp connections and enables a hair-clip structure for concealed placement within the user's hair. Multiple such nodes form a star network coordinated by a master device, which manages communication with a stimulus-presentation computer.To enable cable-free operation while maintaining data integrity, a synchronization strategy was implemented to address timing uncertainties inherent in distributed wireless systems. This strategy combines hardware-event detection with software-based clock management to align stimulus markers with the multi-channel EEG data streams without dedicated synchronization cables. The master device coordinates this process and streams the synchronized data to the computer for real-time processing.System evaluation was conducted in two phases. Foundational performance metrics included physical characteristics, key electrical parameters (input-referred noise: 3.91 μVpp; common-mode rejection ratio: 132.99 dB), and synchronization accuracy across different network scales. Application-level performance was assessed through a 40-command online SSVEP spelling experiment with six subjects in an unshielded room with common RF interference. Four nodes were placed at positions Pz, PO3, PO4, and Oz. EEG epochs (0.14–3.14 s post-stimulus) were analyzed using canonical correlation analysis (CCA) and ensemble task-related component analysis (e-TRCA) to compute recognition accuracy and information transfer rate (ITR). Results and Discussions The implemented system successfully achieved its design objectives. Each acquisition node attained an ultra-compact form factor (3.05 cm3, 3.7 g) suitable for concealed wear, with a battery life exceeding 5 hours at a 1000 Hz sampling rate. The electrical performance confirmed its capability for high-quality SSVEP acquisition.The cable-free synchronization strategy provided the necessary temporal stability for system operation. Evaluation showed that over 95% of event markers were aligned with the EEG data stream with an error of less than 1 millisecond (Fig. 4 ), meeting the requirements for SSVEP-BCI applications. This reliable synchronization contributed to the quality of the recorded neural signals. Grand-averaged SSVEP responses across subjects exhibited clear and stable waveforms with precise phase alignment (Fig. 5 ). The signal-to-noise ratio at the fundamental stimulation frequency exceeded 10 dB for all 40 commands (Fig. 6 ), confirming good signal quality.In the online spelling experiment, the system demonstrated robust decoding performance. Using the e-TRCA algorithm with a 3-second data window, an average recognition accuracy of (95.00 ± 2.04)% was achieved. The system reached a peak ITR of (147.24 ± 30.52) bits/min with a short 0.4-second data length (Fig. 7 ). A comparative analysis with existing SSVEP-BCI systems (Table 1 ) shows that the proposed system, under constraints of miniaturization, cable-free use, and a reduced number of electrodes (four channels), achieved accuracy comparable to some cable-dependent laboratory systems while demonstrating improved wearability.Conclusions This work presents the development and validation of a wearable SSVEP-BCI system that integrates ultra-miniaturized hardware with a distributed, cable-free architecture. The system demonstrates that through coordinated design at the hardware and system levels, it is possible to overcome traditional trade-offs between device size, user freedom, and decoding capability. The acquisition node, at 3.7 g and 3.05 cm3, represents a significant step toward concealable wearability. The implemented synchronization strategy supported reliable operation without dedicated cables. The overall system, evaluated in a realistic environment, delivered online performance competitive with many cable-dependent setups, achieving 95.00% recognition accuracy and a peak ITR of 147.24 bits/min in a 40-target task. Therefore, this study provides a comprehensive system-level solution, contributing a practical platform that facilitates the transition of high-performance BCIs from the laboratory toward everyday wearable applications. -
表 1 不同SSVEP-BCI系统的性能对比
序号 研究 设备 体积(cm3);重量(g) 输入噪声
(μVpp)同步方式/精度(ms) 指令数 使用电极数量(个) 算法:ITR(bits/min)(峰值时间(s));正确率(%)(样本时长(s)) 1 文献[6] Synamps2
商用台式体积834;重量 1500
(仅头盒)0.5 TTL/- 40 9(64导) CCA:267(0.5 s);
91.04%(0.5 s)2 文献[18] ESPW308
商用便携式-/- - 未提及/- 40 4 OACCA:98.46(1.4 s);
91.40%(3.0 s)3 文献[19] LinkMeR
商用便携式体积-;重量75(仅采集
主机)- 未提及/<1 9 8 FBCCA:47.01(2.0 s);
82.22%(3.0 s)4 文献[20] iRecorder W8
商用便携式体积116;重量110
(仅采集主机)<1 额外硬件/≤1 48 8 FBCCA-C:126.11(1.6 s);
85.49%(3 s)5 本研究 自研
隐蔽式体积12.2;重量16.3(4个采集设备+参考电极) 3.91 无线/≤1 40 4(可扩展8) eTRCA:147.24(0.4 s);
95.00%(3.0 s)注:对比设备的体积与重量数据为其采集主机参数,未包含电极、脑电帽等佩戴套件;本研究数据为四个采集从设备与参考电极的总和。 -
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