稳态视觉诱发电位及其在视觉选择性注意研究中的应用

Steady-state visual evoked potential and its applications in studying visual selective attention

以固定频率发生周期性变化的视觉刺激信号进入大脑后,将会诱发一系列与之频率相同的周期性脑电位,这个电位叫做稳态视觉诱发电位(steady-state visual evoked potentials,SSVEP).SSVEP广泛应用于脑机接口和人类认知研究中.相同频率下,SSVEP的振幅高低与视觉注意资源分配具有相关性,因此在视觉选择性注意研究中常常使用SSVEP作为表征注意分配的电生理指标.以SSVEP为指标进行视觉选择性注意研究时,主要的应用手段是频率标记.频率标记是指让被标记刺激发生特定频率的周期性变化,从而诱发与之频率相同的SSVEP,并以每个刺激诱发的SSVEP的振幅作为注意资源分配水平的指标.根据研究目的不同,在频率标记的基础上进一步发展出了快速周期性视觉刺激范式和随机运动点阵范式用于视觉注意的研究.视觉选择性注意中,SSVEP适用于基于空间的注意和基于特征的注意研究.今后使用SSVEP对视觉选择性注意进行研究时,可以试图增加如情绪诱发、奖励和惩罚、工作记忆表征等影响视觉选择性注意的研究变量,也可以以SSVEP为指标,建立基于特征的注意和基于空间的注意之间的联系.此外,脑机接口研究中开发的针对SSVEP的算法也许可引入视觉选择性注意研究中.

Steady-state visual evoked potentials(SSVEP),an evoked brain potential,possesses the same frequency as periodic visual stimuli evoking potentials.It is extensively utilized in Brain-Computer Interface and human cognitive research.Moreover,the amplitude of SSVEP is sensitive to resources allocation of visual selective attention,and therefore can always serve as a corresponding electrophysiological indicator.In comparison with event-related potentials(ERPs)presented by P300 and N2 pc,SSVEP index can be flexibly applied to a variety of paradigms and avoid errors caused by the brain lateralization as different items can be present in the center or in the same region of the view.Furthermore,SSVEP can reflect attention variation because of its continuity and sensibility to attention fluctuation.Besides,ERPs and SSVEP may reflect diverse attentive stages,and certain evidence suggests the attentive stage that SSVEP reflects is earlier compared with ERPs.Specifically,SSVEP may reflect the regulation that brain regions in charge of advanced cognitive function act on the visual cortex or the earlier stage of visual attention.Nevertheless,ERPs might reveal a later stage accomplished by brain regions responsible for higher-order cognitive processes such as the parietal lobe.In the study of visual selective attention,the frequency tagging is primarily employed to induce SSVEP.Visual stimuli are presented periodically at various frequencies to evoke SSVEP so that the stimuli are frequency tagged.We are able to figure out the allocation of attentive resources in those conditions by means of comparing SSVEP amplitude that the same stimulus evokes in a wide range of conditions.The frequency tagging is particularly appropriate to visual selective attention,especially feature-based and space-based attention.Benefiting from its accurate and sensitive reflection of attentive spatial distribution,SSVEP-based frequency tagging is widely adopted in space-based attention and directly proves the attention focus is shape-flexible and dividable but not always a solid circle.On the other hand,researchers developed the random dot kinematograms(RDK)paradigm for feature-based attention,which prolongs instantaneous feature-based attention process so that SSVEP can detect it.With RDK paradigm,researchers find strong evidence that feature-based attention does exist and has a global attentive activation.However,the other kind of visual selective attention,object-based attention,cannot be explored by frequency tagging because periodic flicker will be a highlighted feature so that participants will consider it as an object recognition marker and further destroy the integrity of the object.In the future,researchers can attempt to add emotion,reward and punishment,and working memory representations as research variables,or to build connections between feature-based attention and spatial-based attention in the process of using SSVEP to explore visual selective attention.In addition,the results of BCI algorithms for SSVEP have a potential for being a new visual selective attention index.