Department of Automatic Control, College of Mechatronics and Automation, National University of Defense Technology, Changsha, Hunan 410073, People's Republic of China.
Clin Neurophysiol. 2011 Jun;122(6):1127-36. doi: 10.1016/j.clinph.2010.10.049. Epub 2010 Dec 15.
Brain-computer interface (BCI) provides a mean of communication for the patients that are severely disabled by neuromuscular diseases. The performance of the classical P300 speller, however, declines noticeably in the gaze fixation condition. The speller paradigm presented in this paper aims to release the gaze dependency at the cost of an extra covert visual search task.
Clusters of characters were presented sequentially in the near-central vision as stimulation. Participants fixed their gaze on the center, searched and recognized the target character with covert shift of attention. Random position (RP) and fixed position (FP) presentation modes designed with different searching set size (6 for RP, and ≤ 2 for FP) were examined.
Online sessions using 10 stimulus sequences achieved character accuracies of 94.4% and 96.3% for RP and FP mode, respectively. For offline overall evaluation, the peak written symbol rate (WSR) of 1.38 symbols/min was obtained, with corresponding accuracies of 87.8% (RP) and 84.1% (FP). The P300 waveform of RP mode has evident longer latency and larger amplitude. Electrooculogram (EOG) analysis indicated that the performance was independent of gaze shift.
The proposed speller could be operated effectively and gaze independently by healthy participants.
The proposed gaze independent BCI approach promises reasonable communication capability for the profoundly paralyzed patients with head or ocular motor impairments.
脑机接口（BCI）为患有严重神经肌肉疾病的患者提供了一种交流方式。然而，经典 P300 拼写器的性能在注视固定条件下显著下降。本文提出的拼写器范式旨在释放对注视的依赖，代价是增加一个额外的隐蔽视觉搜索任务。
字符簇以刺激的形式顺序呈现在近中心视野中。参与者注视中心，通过隐蔽的注意力转移搜索并识别目标字符。设计了不同搜索集大小的随机位置（RP）和固定位置（FP）呈现模式（RP 为 6，FP 为 ≤2）。
使用 10 个刺激序列的在线会话，RP 和 FP 模式的字符准确率分别达到 94.4%和 96.3%。对于离线整体评估，获得的峰值书写符号率（WSR）为 1.38 个符号/分钟，相应的准确率为 RP 模式的 87.8%和 FP 模式的 84.1%。RP 模式的 P300 波形潜伏期较长，振幅较大。眼动电图（EOG）分析表明，性能与注视转移无关。
该拼写器可被健康参与者有效地、无需注视地操作。
所提出的无需注视的 BCI 方法有望为头部或眼部运动障碍的严重瘫痪患者提供合理的通信能力。
