Center for Mind and Brain, University of California, Davis, California 95616,
Escuela de Psicología, Facultad de Ciencias Sociales, Pontificia Universidad Católica de Chile, Santiago, Chile.
J Neurosci. 2019 Jan 30;39(5):900-917. doi: 10.1523/JNEUROSCI.0183-18.2018. Epub 2018 Dec 6.
Alpha-band (8-12 Hz) EEG activity has been linked to visual attention since the earliest EEG studies. More recent studies using spatial cuing paradigms have shown that alpha is suppressed over the hemisphere contralateral to a to-be-attended location, suggesting that alpha serves as a mechanism of preparatory attention. Here, we demonstrate that alpha also plays a role in active target processing. EEG activity was recorded from a group of healthy male and female human subjects in two visual search experiments. In addition to alpha activity, we also assessed the N2pc event-related potential component, a lateralized transient EEG response that has been tightly linked with the focusing of attention on visual targets. We found that the visual search targets triggered both an N2pc component and a suppression of alpha-band activity that was greatest over the hemisphere contralateral to the target (which we call "target-elicited lateralized alpha suppression" or TELAS). In Experiment 1, both N2pc and TELAS were observed for targets presented in the lower visual field but were absent for upper-field targets. However, these two lateralized effects had different time courses and they responded differently to manipulations of crowding in Experiment 2. These results indicate that lateralized alpha-band activity is involved in active target processing and is not solely a preparatory mechanism and also that TELAS and N2pc reflect a related but separable neural mechanism of visuospatial attention. The very first EEG studies demonstrated that alpha-band (8-12 Hz) EEG oscillations are suppressed when people attend to visual information and more recent research has shown that cuing an individual to expect a target at a specific location produces lateralized suppression in the contralateral hemisphere. Therefore, lateralized alpha may serve as a preparatory mechanism. In the present study, we found that a similar lateralized alpha effect is triggered by the appearance of a visual target even though the location could not be anticipated, demonstrating that alpha also serves as an active mechanism of target processing. Moreover, we found that alpha lateralization can be dissociated from other lateralized measures of target selection, indicating that it reflects a distinct mechanism of attention.
alpha 波段（8-12Hz）脑电活动自最早的脑电研究以来就与视觉注意力有关。最近使用空间提示范式的研究表明，alpha 波在即将被注意的位置的对侧半球受到抑制，这表明 alpha 波作为预备注意的机制。在这里，我们证明 alpha 波也在主动目标处理中发挥作用。我们在两个视觉搜索实验中记录了一组健康男性和女性人类受试者的脑电图活动。除了 alpha 活动，我们还评估了 N2pc 事件相关电位成分，这是一种与视觉目标注意力集中紧密相关的侧化瞬态脑电反应。我们发现，视觉搜索目标既引发了 N2pc 成分，也引发了 alpha 波段活动的抑制，这种抑制在目标对侧的半球最大（我们称之为“目标诱发的侧化 alpha 抑制”或 TELAS）。在实验 1 中，在较低的视觉场中呈现目标时观察到 N2pc 和 TELAS，但在较高的视觉场中没有观察到目标。然而，这两种侧化效应具有不同的时间过程，并且它们对实验 2 中拥挤的操纵反应不同。这些结果表明，侧化 alpha 波段活动参与主动目标处理，而不仅仅是预备机制，并且 TELAS 和 N2pc 反映了一种相关但可分离的视觉空间注意力神经机制。最早的 EEG 研究表明，当人们关注视觉信息时，alpha 波段（8-12Hz）脑电波振荡会被抑制，而最近的研究表明，提示个体在特定位置期待目标会导致对侧半球的侧化抑制。因此，侧化 alpha 可能作为一种预备机制。在本研究中，我们发现即使位置无法预测，视觉目标的出现也会引发类似的侧化 alpha 效应，这表明 alpha 波也作为目标处理的主动机制。此外，我们发现 alpha 侧化可以与其他侧化的目标选择测量分开，表明它反映了一种不同的注意力机制。
