独立式脑—计算机接口的离线实验及分析

Off-line Experiments and Analysis of Independent Brain—Computer Interface

设计两个实验以研究自主运动的事件相关去同步模式的特征。实验一:要求未经训练的被试者在提示出现后开始想像用食指按键的动作,并在1 s后实际按键;实验二:作为参照,要求被试者对提示立即反应,使动作想像的时间尽量缩短。通过分析提示与实际动作之间的自发脑电信号,预测被试者用左手或右手按键。在实验一的连续测试中,预测率随测试进行由85%下降到71%;而实验二的预测率近乎随机猜测。结果表明:(1)运动想像的有效持续时间对事件相关去同步模式有显著影响;(2)被试者有效动作想像时间的不自觉地缩短会导致预测率的明显下降。如何保证被试者的有效动作想像时间是后续实验设计中应该重视的问题。

In order to study event-related desynchronization （ERD） related to voluntary movement, we designed two experiments. In the first experiment, untrained subjects were required to imagine the action of typing with left or right index finger for about 1 second before real action, whereas they were required to type instantly after instruction in the second experiment. By analyzing spontaneous EEG singals between the instruction and the action, we predicted which finger was used. The prediction accuracy in the first experiment fell from 85% to 71% with the progress of experiment, the average accuracy being 78%, whereas the prediction result was almost random guess in the second experiment. The results demonstrate that （1） ERD patterns are significantly affected by the effective duration of motion imagination, （2） unconscious reduction of this duration can decrease the prediction accuracy. Therefore, when designing subsequent BCI experiments, we should devote our attention to the question of how to keep the effective duration of motion imagination.