Department of Neurology, Otto-von-Guericke University and Leibniz Institute for Neurobiology, Magdeburg 39120, Germany.
J Neurosci. 2011 Apr 6;31(14):5213-24. doi: 10.1523/JNEUROSCI.6406-10.2011.
Visual attention biases relevant processing in the visual system by amplifying relevant or attenuating irrelevant sensory input. A potential signature of the latter operation, referred to as surround attenuation, has recently been identified in the electromagnetic brain response of human observers performing visual search. It was found that a zone of attenuated cortical excitability surrounds the target when the search required increased spatial resolution for item discrimination. Here we address the obvious hypothesis that surround attenuation serves distractor suppression in the vicinity of the target where interference from irrelevant search items is maximal. To test this hypothesis, surround attenuation was assessed under conditions when the target was presented in isolation versus when it was surrounded by distractors. Surprisingly, substantial and indistinguishable surround attenuation was seen under both conditions, indicating that it reflects an attentional operation independent of the presence of distractors. Adding distractors in the target's surround, however, increased the amplitude of the N2pc--an evoked response known to index distractor competition in visual search. Moreover, adding distractors led to a topographical change of source activity underlying the N2pc toward earlier extrastriate areas. In contrast, the topography of reduced source activity due to surround attenuation remained unaltered with and without distractors in the target's surround. We conclude that surround attenuation is not a direct consequence of the attenuation of distractors in visual search and that it dissociates from attentional operations reflected by the N2pc. A theoretical framework is proposed that links both operations in a common model of top-down attentional selection in visual cortex.
视觉注意力通过放大相关或衰减不相关的感觉输入来偏向视觉系统中的相关处理。最近，在人类观察者进行视觉搜索时的电磁脑反应中，已经确定了后一种操作（称为环绕衰减）的潜在特征。当搜索需要增加项目辨别力的空间分辨率时，发现目标周围存在衰减的皮质兴奋性区域。在这里，我们提出了一个明显的假设，即环绕衰减在目标附近的干扰最大的情况下抑制分心物。为了检验这一假设，我们评估了在目标单独呈现与目标周围存在分心物时的环绕衰减情况。令人惊讶的是，在这两种情况下都观察到了大量且无法区分的环绕衰减，这表明它反映了一种与分心物存在无关的注意力操作。然而，在目标周围添加分心物会增加 N2pc 的振幅——这是一种在视觉搜索中指示分心物竞争的诱发反应。此外，添加分心物导致 N2pc 下源活动的地形图发生变化，向早期的外纹状体区域移动。相比之下，由于环绕衰减导致的源活动减少的地形图在目标周围有或没有分心物时保持不变。我们得出结论，环绕衰减不是视觉搜索中分心物衰减的直接结果，它与 N2pc 反映的注意力操作是分离的。我们提出了一个理论框架，将这两种操作链接到一个共同的视觉皮层自上而下注意选择模型中。
