Toward a common circle: Interhemispheric contextual modulation in human early visual areas
Toward a common circle: Interhemispheric contextual modulation in human early visual areas
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DOI：
10.1523/jneurosci.1765-06.2006
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发表时间：
2006-08-23
影响因子：
5.3
通讯作者：
Ejima, Yoshimichi
中科院分区：
文献类型：
--
作者：
Ban, Hiroshi;Yamamoto, Hiroki;Ejima, Yoshimichi
人类可以毫不费力地从复杂的视觉场景中感知到丰富、稳定、统一的视觉世界。然而，我们对视觉对象的内部表征似乎是稀疏和碎片化的。在大脑中，这些碎片化的表象是如何以及在哪里被组织成一个完整的感知的？近年来的研究表明，在视觉加工的早期阶段，某些整体特征整合是介导的。然而，一体化的空间运行范围仍不明确。目前的人类功能磁共振成像研究支持了早期视觉区域的整体整合过程，甚至包括初级视觉区域V1，是通过从固定物的左右两侧的视觉半球分离投射到对侧大脑半球的视觉皮层而介导的。当另一个目标同时出现在非相关视野象限的点对称位置时，视觉目标对应的视网膜定位神经反应显著增强。这一结果令人信服地证明，上下文效应涉及来自较高区域的反馈，因为没有直接的胼胝体连接允许这种半球间的上下文调制。这种来自同侧半球的增强可能有助于快速检测圆形图案的位置和大小不变，圆形图案在视觉结构中可能是特殊的，因为它在自然场景中无处不在。早期视觉区域和高级视觉区域可能在感知现实世界的统一性方面发挥着比以前认为的更重要的作用。
Humans can readily and effortlessly perceive a rich, stable, and unified visual world from a complex visual scene. Yet our internal representation of a visual object appears to be sparse and fragmented. How and where in the brain are such fragmented representations organized into a whole percept? Recent studies have accumulated evidence that some global feature integration is mediated at the early stage of visual processing. However, the spatial operating range of the integration still remains unclear. The present human functional magnetic resonance imaging study provides support that the global integration process in early visual areas, including even the primary visual area V1, is mediated beyond the separated projection of visual hemifields from right and left sides of the fixation to the visual cortex of the contralateral cerebral hemisphere. Retinotopic neural responses corresponding to a visual target were significantly enhanced when another target was simultaneously presented at the point-symmetrical position in the nonassociated visual field quadrant. The result makes a convincing case that the contextual effects involve feedback from higher areas, because there are no direct callosal connections that allow such interhemispheric contextual modulation. This enhancement from the ipsilateral hemifield may help rapid position-and-size-invariant detection of a circular pattern, which may be special among visual structures because of its ubiquity in natural scenes. Early visual areas as well as higher ones may play a more essential role in perceiving the unity of the real world than previously thought.