Liu Zhongming, Zhang Nanyin, Chen Wei, He Bin
Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
Neuroimage. 2009 Jul 15;46(4):989-97. doi: 10.1016/j.neuroimage.2009.03.028. Epub 2009 Mar 20.
In the human visual system, the internal representation of the left and right visual hemifields is split at the midline of the two cerebral hemispheres. The present study aims to address the questions of when and where the lateralized cortical visual representations are merged to form an intact percept by using a multimodal neuroimaging approach. Visual evoked potential (VEP) and functional magnetic resonance imaging (fMRI) data were acquired from a group of healthy subjects presented with unilateral versus bilateral visual stimuli. Cortical activities involved in processing bilateral visual information are expected to be equally responsive to ipsilateral and contralateral stimuli, and demonstrate spatial nonlinearity in the response to bilateral stimuli. Utilizing these features, we performed integrative as well as separate analyses for both VEP and fMRI data. The present results suggest that i) the majority of cortical activity that integrates visual information across hemifields takes place at extrastriate areas during late visual processing, and that ii) the lateral occipito-temporal (LOT) regions (likely the MT+ complex) and the medial occipital cortex (i.e. V1) may contribute to bilateral visual integration during early visual processing. Our findings are generally in agreement with the bottom-up visual hierarchy, with the exception of the evidence suggesting an early activation of the higher-tier LOT areas and the influence from ipsilateral visual inputs upon the V1 response.
在人类视觉系统中，左右视觉半视野的内部表征在两个大脑半球的中线处分开。本研究旨在通过使用多模态神经成像方法来解决侧向化的皮质视觉表征何时以及在何处合并以形成完整感知的问题。从一组接受单侧与双侧视觉刺激的健康受试者获取视觉诱发电位（VEP）和功能磁共振成像（fMRI）数据。处理双侧视觉信息所涉及的皮质活动预计对同侧和对侧刺激具有同等反应，并在对双侧刺激的反应中表现出空间非线性。利用这些特征，我们对VEP和fMRI数据进行了综合分析以及单独分析。目前的结果表明：i）在晚期视觉处理过程中，跨半视野整合视觉信息的大部分皮质活动发生在纹外区域；ii）外侧枕颞（LOT）区域（可能是MT +复合体）和内侧枕叶皮质（即V1）可能在早期视觉处理过程中有助于双侧视觉整合。我们的发现总体上与自下而上的视觉层级一致，但有证据表明较高层级的LOT区域早期激活以及同侧视觉输入对V1反应的影响除外。
