Department of Cognitive Biology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria; Language Research Laboratory, Lisbon Faculty of Medicine, Av. Professor Egas Moniz, 1649-028 Lisboa, Portugal.
Medical University of Vienna, Department of Neurology, High-Field MR Center of Excellence, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
Neuroimage. 2014 Aug 1;96:300-8. doi: 10.1016/j.neuroimage.2014.03.064. Epub 2014 Mar 31.
Hierarchical structures play a central role in many aspects of human cognition, prominently including both language and music. In this study we addressed hierarchy in the visual domain, using a novel paradigm based on fractal images. Fractals are self-similar patterns generated by repeating the same simple rule at multiple hierarchical levels. Our hypothesis was that the brain uses different resources for processing hierarchies depending on whether it applies a "fractal" or a "non-fractal" cognitive strategy. We analyzed the neural circuits activated by these complex hierarchical patterns in an event-related fMRI study of 40 healthy subjects. Brain activation was compared across three different tasks: a similarity task, and two hierarchical tasks in which subjects were asked to recognize the repetition of a rule operating transformations either within an existing hierarchical level, or generating new hierarchical levels. Similar hierarchical images were generated by both rules and target images were identical. We found that when processing visual hierarchies, engagement in both hierarchical tasks activated the visual dorsal stream (occipito-parietal cortex, intraparietal sulcus and dorsolateral prefrontal cortex). In addition, the level-generating task specifically activated circuits related to the integration of spatial and categorical information, and with the integration of items in contexts (posterior cingulate cortex, retrosplenial cortex, and medial, ventral and anterior regions of temporal cortex). These findings provide interesting new clues about the cognitive mechanisms involved in the generation of new hierarchical levels as required for fractals.
层次结构在人类认知的许多方面都起着核心作用，特别是包括语言和音乐。在这项研究中，我们使用基于分形图像的新范式来研究视觉领域的层次结构。分形是通过在多个层次上重复相同的简单规则生成的自相似模式。我们的假设是，大脑根据其使用的是“分形”还是“非分形”认知策略，来处理不同的层次结构。我们分析了 40 名健康受试者进行的事件相关 fMRI 研究中这些复杂层次模式激活的神经回路。通过三个不同的任务比较大脑激活情况：相似性任务，以及两个层次任务，要求受试者识别在现有层次内或生成新层次的规则操作转换的重复。相似的层次图像由两种规则生成，而目标图像则相同。我们发现，在处理视觉层次结构时，参与这两个层次任务会激活视觉背侧流（枕顶叶皮层、顶内沟和背外侧前额叶皮层）。此外，生成层次的任务特别激活了与空间和类别信息整合以及在上下文中整合项目有关的回路（后扣带皮层、后扣带回皮层以及颞叶的内侧、腹侧和前区）。这些发现为分形所需的新层次生成所涉及的认知机制提供了有趣的新线索。
