Burrows Brittany E, Moore Tirin
Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305, USA.
J Neurosci. 2009 Dec 2;29(48):15169-77. doi: 10.1523/JNEUROSCI.3710-09.2009.
The neural mechanism of bottom-up attention and its relationship to top-down attention are poorly understood. Visual stimuli that differ from others in their component features are salient and tend to draw attention in a bottom-up manner. "Popout" stimuli differ uniformly from surrounding items and are more easily detected than stimuli composed of a conjunction of surrounding features. We compared the responses of single area V4 neurons to popout and conjunction stimuli appearing within the classical receptive field (CRF) and found that their responses are modulated by popout. This selectivity was more robust when larger numbers of surrounding items and multiple features were included in the display, and it was absent when only a few items were presented immediately outside the CRF. In addition, the popout modulation of V4 activity was eliminated when top-down attention was directed to locations outside of the CRFs during saccade preparation, indicating that the salience of popout stimuli is not sufficient to drive selection by V4 neurons. These results demonstrate that neurons in feature-selective cortex are influenced by bottom-up attention, but that this influence is limited by top-down attention.
自下而上的注意力的神经机制及其与自上而下的注意力的关系目前还知之甚少。在组成特征上与其他刺激不同的视觉刺激是显著的，并且倾向于以自下而上的方式吸引注意力。“突现”刺激与周围项目均匀不同，并且比由周围特征组合而成的刺激更容易被检测到。我们比较了单个V4区神经元对出现在经典感受野（CRF）内的突现刺激和组合刺激的反应，发现它们的反应受到突现的调节。当显示中包含更多数量的周围项目和多种特征时，这种选择性更强；而当仅在CRF之外紧邻呈现少数项目时，这种选择性则不存在。此外，在扫视准备期间，当自上而下的注意力指向CRF之外的位置时，V4活动的突现调制被消除，这表明突现刺激的显著性不足以驱动V4神经元进行选择。这些结果表明，特征选择性皮层中的神经元受到自下而上的注意力的影响，但这种影响受到自上而下的注意力的限制。
