Harvey Ben M, Fracasso Alessio, Petridou Natalia, Dumoulin Serge O
Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht 3584 CS, The Netherlands; Faculty of Psychology and Education Sciences, University of Coimbra, 3001-802 Coimbra, Portugal;
Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht 3584 CS, The Netherlands; Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht 3584 CX, The Netherlands.
Proc Natl Acad Sci U S A. 2015 Nov 3;112(44):13525-30. doi: 10.1073/pnas.1515414112. Epub 2015 Oct 19.
Humans and many animals analyze sensory information to estimate quantities that guide behavior and decisions. These quantities include numerosity (object number) and object size. Having recently demonstrated topographic maps of numerosity, we ask whether the brain also contains maps of object size. Using ultra-high-field (7T) functional MRI and population receptive field modeling, we describe tuned responses to visual object size in bilateral human posterior parietal cortex. Tuning follows linear Gaussian functions and shows surround suppression, and tuning width narrows with increasing preferred object size. Object size-tuned responses are organized in bilateral topographic maps, with similar cortical extents responding to large and small objects. These properties of object size tuning and map organization all differ from the numerosity representation, suggesting that object size and numerosity tuning result from distinct mechanisms. However, their maps largely overlap and object size preferences correlate with numerosity preferences, suggesting associated representations of these two quantities. Object size preferences here show no discernable relation to visual position preferences found in visuospatial receptive fields. As such, object size maps (much like numerosity maps) do not reflect sensory organ structure but instead emerge within the brain. We speculate that, as in sensory processing, optimization of cognitive processing using topographic maps may be a common organizing principle in association cortex. Interactions between object size and numerosity maps may associate cognitive representations of these related features, potentially allowing consideration of both quantities together when making decisions.
人类和许多动物会分析感官信息，以估算引导行为和决策的数量。这些数量包括数量（物体数量）和物体大小。鉴于最近已证实存在数量地形图，我们不禁要问，大脑中是否也存在物体大小的地图。利用超高场（7T）功能磁共振成像和群体感受野建模，我们描述了双侧人类顶叶后皮质对视觉物体大小的调谐反应。调谐遵循线性高斯函数并表现出周围抑制，且调谐宽度随着偏好物体大小的增加而变窄。物体大小调谐反应在双侧地形图中组织起来，对大物体和小物体做出反应的皮质范围相似。物体大小调谐和地图组织的这些特性均与数量表征不同，这表明物体大小和数量调谐是由不同机制产生的。然而，它们的地图在很大程度上重叠，且物体大小偏好与数量偏好相关，这表明这两个数量存在相关表征。此处的物体大小偏好与在视觉空间感受野中发现的视觉位置偏好没有明显关系。因此，物体大小地图（很像数量地图）并不反映感觉器官结构，而是在大脑中形成。我们推测，如同在感觉处理中一样，利用地形图对认知处理进行优化可能是联合皮质中的一种常见组织原则。物体大小地图和数量地图之间的相互作用可能会关联这些相关特征的认知表征，从而有可能在做出决策时同时考虑这两个数量。
