Experimental Psychology, University College London, 26 Bedford Way, London, WC1H 0AP, UK.
Experimental Psychology, University College London, 26 Bedford Way, London, WC1H 0AP, UK.
Neuroimage. 2020 Oct 15;220:116926. doi: 10.1016/j.neuroimage.2020.116926. Epub 2020 May 19.
Our visual system readily groups dynamic fragmented input into global objects. How the brain represents global object perception remains however unclear. To address this question, we recorded brain responses using functional magnetic resonance imaging whilst observers viewed a dynamic bistable stimulus that could either be perceived globally (i.e., as a grouped and coherently moving shape) or locally (i.e., as ungrouped and incoherently moving elements). We further estimated population receptive fields and used these to back-project the brain activity measured during stimulus perception into visual space via a searchlight procedure. Global perception resulted in universal suppression of responses in lower visual cortex accompanied by wide-spread enhancement in higher object-sensitive cortex. However, follow-up experiments indicated that higher object-sensitive cortex is suppressed if global perception lacks shape grouping, and that grouping-related suppression can be diffusely confined to stimulated sites and accompanied by background enhancement once stimulus size is reduced. These results speak to a non-generic involvement of higher object-sensitive cortex in perceptual grouping and point to an enhancement-suppression mechanism mediating the perception of figure and ground.
我们的视觉系统能够轻易地将动态碎片化的输入组合成整体对象。然而，大脑如何表示整体对象感知仍然不清楚。为了解决这个问题，我们在观察者观看动态双稳态刺激时使用功能磁共振成像记录大脑反应，该刺激可以整体感知（即，作为一个分组且连贯运动的形状）或局部感知（即，作为未分组且非连贯运动的元素）。我们进一步估计了群体感受野，并使用这些感受野通过搜索灯程序将在刺激感知期间测量的大脑活动反向投影到视觉空间中。整体感知导致下视皮质的反应普遍受到抑制，同时在更高的物体敏感皮质中广泛增强。然而，后续实验表明，如果全局感知缺乏形状分组，则更高的物体敏感皮质会受到抑制，并且一旦刺激大小减小，分组相关的抑制就可以扩散到刺激部位，并伴有背景增强。这些结果表明，更高的物体敏感皮质参与了知觉分组，并且指向了一种增强-抑制机制，该机制调节了图形和背景的感知。
