Bi Taiyong, Cai Peng, Zhou Tiangang, Fang Fang
Department of Psychology and Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing, PR China.
J Vis. 2009 Oct 14;9(11):13.1-10. doi: 10.1167/9.11.13.
Crowding is the identification difficulty for a target in the presence of nearby flankers. Based on psychophysical findings, many theories have been proposed to explain crowding at multiple levels. However, little is known about its neural mechanism. In this study, we combined psychophysical and fMRI adaptation techniques to search for the cortical locus of crowding. In the psychophysical experiment, when subjects' attention was controlled, we found that the threshold elevation aftereffect (TEAE) was not affected by crowding, regardless of the contrast level of adapting stimulus. In the fMRI experiment, the orientation-selective fMRI adaptation in V1 was not affected by crowding either. However, downstream from V1, we found that crowding weakened the adaptation effect in V2 and V3. Our results demonstrate that crowding occurs beyond V1 and provide one of the first pieces of direct evidence supporting the two-stage model of crowding (D. M. Levi, 2008).
拥挤效应是指在存在附近侧翼干扰物的情况下对目标的识别困难。基于心理物理学研究结果，人们提出了许多理论来在多个层面解释拥挤效应。然而，对于其神经机制却知之甚少。在本研究中，我们结合心理物理学和功能磁共振成像适应技术来寻找拥挤效应的皮层位点。在心理物理学实验中，当控制受试者的注意力时，我们发现阈值升高后效（TEAE）不受拥挤效应的影响，无论适应刺激的对比度水平如何。在功能磁共振成像实验中，V1区的方向选择性功能磁共振成像适应也不受拥挤效应的影响。然而，在V1区的下游，我们发现拥挤效应减弱了V2区和V3区的适应效果。我们的结果表明，拥挤效应发生在V1区之外，并提供了支持拥挤效应两阶段模型（D. M. Levi，2008）的首批直接证据之一。
