Functional Anatomy Of Perceptual And Memory Systems In T

一个典型的场景包含许多不同的对象，由于视觉系统的处理能力有限，这些对象竞争神经表示。在神经水平上，多个刺激之间的竞争表现为它们的视觉诱发反应的相互抑制，并且最强烈地发生在接受野水平。多个对象之间的竞争可能会受到自下而上的感官驱动机制和自上而下的影响(如选择性注意)的影响。脑功能成像研究表明，选择性注意引起的偏向信号不仅在有视觉刺激的情况下，而且在没有视觉刺激的情况下，都可以调节视觉皮质的神经活动。虽然刺激之间对表征的竞争最终在视觉皮质内解决，但自上而下的偏向信号的来源可能来自额叶和顶叶皮质区域的分布网络。这种有偏见的注意力竞争模型表明，一旦注意力资源耗尽，就不可能进行进一步的处理。然而，现有的数据表明，情绪刺激“自动”激活大脑区域，很大程度上不受注意力控制。我们测试了另一种可能性，即对带有情绪内容的刺激的神经处理不是自动的，相反需要一定程度的注意。我们的结果显示，与流行的观点相反，所有对情绪面孔做出不同反应的大脑区域，包括杏仁核，只有在有足够的注意力资源来处理面孔时才会这样做。因此，与其他刺激类别的加工类似，面部表情的加工是自上而下控制的。

A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies reveal that biasing signals due to selective attention can modulate neural activity in visual cortex not only in the presence but also in the absence of visual stimulation. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. This biased competition model of attention suggests that once attentional resources are depleted, no further processing is possible. Yet, existing data suggest that emotional stimuli activate brain regions "automatically," largely immune from attentional control. We tested the alternative possibility, namely, that the neural processing of stimuli with emotional content is not automatic and instead requires some degree of attention. Our results revealed that, contrary to the prevailing view, all brain regions responding differentially to emotional faces, including the amygdala, did so only when sufficient attentional resources were available to process the faces. Thus, similar to the processing of other stimulus categories, the processing of facial expression is under top-down control.