Department of Neurology, University of Lübeck, Lübeck, Germany.
PLoS One. 2013;8(2):e57421. doi: 10.1371/journal.pone.0057421. Epub 2013 Feb 22.
Little is known about how the hemispheres interact in processing of stimuli presented at vertical midline. Processing might be mutually independent or cooperative. Here we measured target identification and visually evoked EEG potentials while stimulus streams containing two targets, T1 and T2, were either presented at vertical midline above and below fixation, or laterally, left and right. With left and right streams, potentials evoked by filler stimuli and by T2 were earlier at the right than the left visual cortex, and T2 was better identified left than right, confirming earlier results and suggesting better capabilities of the right hemisphere in this task. With streams above and below fixation, EEG potentials evoked by filler stimuli and by T2 were likewise earlier at the right than the left hemisphere, and T2 was generally identified as well as, but not better than left T2, in one target constellation even worse (T2 in lower stream preceded by T1 in upper stream). These results suggest right-hemisphere preference for this task even with stimuli at vertical midline, and no added value through hemispheric cooperation. Lacking asymmetry for T1 amidst asymmetries for filler stimuli and for T2 might indicate alternating access of the hemispheres to midline stimuli as one means of hemispheric division of labor.
目前对于在垂直中线呈现的刺激，大脑两半球是如何相互作用进行处理的还知之甚少。这种处理可能是相互独立的，也可能是相互协作的。在这里，我们测量了当刺激流中包含两个目标 T1 和 T2 时，目标的识别和视觉诱发电位，这些刺激流分别在注视点上方和下方的垂直中线上呈现，或者在左右两侧呈现。在左右刺激流中，由填充刺激和 T2 诱发的电位在右视觉皮层比左视觉皮层更早出现，而 T2 在左侧比右侧更容易被识别，这证实了之前的结果，并表明在这个任务中右半球具有更好的能力。在注视点上方和下方的刺激流中，由填充刺激和 T2 诱发的脑电电位在右半球比左半球更早出现，并且 T2 在一个目标配置中与左侧 T2 一样容易被识别，但在另一个目标配置中（T2 在上面的流中，T1 在下面的流中）却不如左侧 T2 识别得好。这些结果表明，即使在垂直中线呈现刺激时，右半球也更倾向于执行这项任务，而且没有通过半球间的协作获得额外的优势。在填充刺激和 T2 存在不对称性的情况下，T1 缺乏不对称性可能表明，大脑半球交替地访问中线刺激，这是半球分工的一种手段。
