Fang Fang, Boyaci Huseyin, Kersten Daniel, Murray Scott O
Department of Psychology, Peking University, Beijing 100871, People's Republic of China.
Curr Biol. 2008 Nov 11;18(21):1707-12. doi: 10.1016/j.cub.2008.09.025.
One of the most fundamental properties of human primary visual cortex (V1) is its retinotopic organization, which makes it an ideal candidate for encoding spatial properties, such as size, of objects. However, three-dimensional (3D) contextual information can lead to size illusions that are reflected in the spatial pattern of activity in V1 [1]. A critical question is how complex 3D contextual information can influence spatial activity patterns in V1. Here, we assessed whether changes in the spatial distribution of activity in V1 depend on the focus of attention, which would be suggestive of feedback of 3D contextual information from higher visual areas. We presented two 3D rings at close and far apparent depths in a 3D scene. When subjects fixated its center, the far ring appeared to be larger and occupy a more eccentric portion of the visual field, relative to the close ring. Using functional magnetic resonance imaging, we found that the spatial distribution of V1 activity induced by the far ring was also shifted toward a more eccentric representation of the visual field, whereas that induced by the close ring was shifted toward the foveal representation, consistent with their perceptual appearances. This effect was significantly reduced when the focus of spatial attention was narrowed with a demanding central fixation task. We reason that focusing attention on the fixation task resulted in reduced activity in--and therefore reduced feedback from--higher visual areas that process the 3D depth cues.
人类初级视觉皮层（V1）最基本的特性之一是其视网膜拓扑组织，这使其成为编码物体空间属性（如大小）的理想候选者。然而，三维（3D）上下文信息会导致大小错觉，这在V1的空间活动模式中有所体现[1]。一个关键问题是复杂的3D上下文信息如何影响V1中的空间活动模式。在这里，我们评估了V1中活动的空间分布变化是否取决于注意力焦点，这将暗示来自更高视觉区域的3D上下文信息的反馈。我们在一个3D场景中呈现了两个处于近和远视深度的3D环。当受试者注视环的中心时，相对于近环，远环看起来更大且占据视野中更偏心的部分。使用功能磁共振成像，我们发现远环诱导的V1活动的空间分布也向视野中更偏心的表征转移，而近环诱导的则向中央凹表征转移，这与它们的感知外观一致。当通过一项要求较高的中央注视任务使空间注意力焦点变窄时，这种效应会显著降低。我们推断，将注意力集中在注视任务上会导致处理3D深度线索的更高视觉区域的活动减少，从而减少反馈。
