Fischer Jason, Whitney David
The Department of Psychology, and The Center for Mind and Brain, The University of California, Davis, Davis, CA 95616, USA.
Curr Biol. 2009 Aug 25;19(16):1356-61. doi: 10.1016/j.cub.2009.06.059. Epub 2009 Jul 23.
When attention is directed to a region of space, visual resolution at that location flexibly adapts, becoming sharper to resolve fine-scale details or coarser to reflect large-scale texture and surface properties. By what mechanism does attention improve spatial resolution? An improved signal-to-noise ratio (SNR) at the attended location contributes, because of retinotopically specific signal gain. Additionally, attention could sharpen position tuning at the neural population level, so that adjacent objects activate more distinct regions of the visual cortex. A dual mechanism involving both signal gain and sharpened position tuning would be highly efficient at improving visual resolution, but there is no direct evidence that attention can narrow the position tuning of population responses. Here, we compared the spatial spread of the fMRI BOLD response for attended versus ignored stimuli. The activity produced by adjacent stimuli overlapped less when subjects were attending at their locations versus attending elsewhere, despite a stronger peak response with attention. Our results show that even as early as primary visual cortex (V1), spatially directed attention narrows the tuning of population-coded position representations.
当注意力指向空间中的某个区域时，该位置的视觉分辨率会灵活调整，变得更敏锐以分辨精细细节，或更粗糙以反映大规模纹理和表面属性。注意力通过何种机制提高空间分辨率呢？由于视网膜拓扑特异性信号增益，被关注位置处改善的信噪比（SNR）起了作用。此外，注意力可能会在神经群体水平上锐化位置调谐，使得相邻物体激活视觉皮层中更不同的区域。涉及信号增益和锐化位置调谐的双重机制在提高视觉分辨率方面将非常高效，但尚无直接证据表明注意力能够缩小群体反应的位置调谐。在此，我们比较了被关注与被忽略刺激的功能磁共振成像（fMRI）血氧水平依赖（BOLD）反应的空间扩展。尽管注意力会使峰值反应更强，但当受试者关注刺激的位置而非其他位置时，相邻刺激产生的活动重叠更少。我们的结果表明，即使早在初级视觉皮层（V1），空间定向注意力也会缩小群体编码位置表征的调谐。
