视觉拥挤效应的神经机制

Visual crowding effect is the identification difficulty for a target in the presence of nearby flankers. It is not only an essential bottleneck for object recognition, but also associated with some clinical diseases (e.g. amblyopia and degeneration). As a hot research topic, visual crowding effect is on the cutting edge of cognitive neuroscience research. However, we still know little about its neural mechanisms though the existence of so many theoretical debates. A major reason is that visual crowding research is difficult to perform, thus not much brain imaging and neurophysiological data available. Here, we will combine psychophysics, functional magnetic resonance imaging and transcranial magnetic stimulation to study visual crowding effect systematically and comprehensively. Previous studies have demonstrated that visual crowding manifested as an attention-dependent suppressive cortical interaction between the target and flankers in early visual areas, which suggested that crowding might occur at both low-level and high-level areas in the visual system. Thus, this project contains two parts: (1) In early visual areas, where and how do visual crowding occur? (2) In the attention network, which areas play critical roles in visual crowding effect? How do they interact with the early visual areas? The project will contribute to our understanding of the neural mechanisms of visual crowding effect systematically and comprehensively.

视觉拥挤效应是指当一个物体被其它物体包围时，对该物体的识别会受到周围物体的影响。视觉拥挤效应不仅被认为是视觉系统进行物体识别的重要瓶颈，而且还与弱视、黄斑变性等多种临床疾病有关。视觉拥挤效应是目前认知神经科学研究的前沿问题和热点问题，对它的神经机制研究具有理论争议多、研究难度大、脑成像数据少等特点。我们将结合心理物理学、功能性磁共振成像技术以及经颅磁刺激技术对视觉拥挤效应的神经机制进行系统的探讨。基于已有的发现，视觉拥挤效应不仅与视觉加工阶段有关，也受到注意的影响，本项目分为两个研究部分。第一个部分研究在视觉加工阶段，哪些早期视觉皮层是视觉拥挤效应的关键脑区，以及它们参与视觉拥挤过程的机制；第二个部分研究在注意阶段，哪些高级皮层是视觉拥挤效应的关键脑区，这些高级皮层与早期视觉皮层之间有怎样的相互作用机制。本项目将力图系统地、全面地揭示视觉拥挤效应的神经机制。

视觉拥挤效应是指当一个物体被其它物体包围时，对该物体的识别会受到周围物体的影响。视觉拥挤效应被认为是视觉系统进行物体识别的重要瓶颈，对它的神经机制研究具有理论争议多、研究难度大、脑成像数据少等特点。本项目结合心理物理学、功能性磁共振成像技术以及经颅电刺激技术对视觉拥挤效应的神经机制进行系统的探讨。本项目分为两个研究部分。第一个部分利用基于功能磁共振成像的群感受野技术研究视觉朝向拥挤发生的皮层位置及神经机制，发现视觉皮层V2的群感受野大小在视觉朝向拥挤过程中起着关键性的作用；第二个部分探讨在视皮层施加经颅直流电刺激对拥挤效应的影响，发现在枕叶施加阳极直流电刺激之后，拥挤效应被显著削弱，并且这种削弱作用不局限与特定的空间位置或任务类型。本项目为视觉拥挤效应的认知神经机制从心理物理层面到脑成像和神经调控层面提供了原创的、系统性的实验与理论证据。

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