Green Michael F, Glahn David, Engel Stephen A, Nuechterlein Keith H, Sabb Fred, Strojwas Magda, Cohen Mark S
Department of Psychiatry and Behavioral Sciences, Geffen School of Medicine at University of California, Los Angeles, CA 90095-6968, USA.
J Cogn Neurosci. 2005 Jan;17(1):13-23. doi: 10.1162/0898929052880011.
In visual backward masking, the visibility of a briefly presented visual target is disrupted by a mask that is presented shortly thereafter. The goal of the current study was to identify regions in the human cortex that may provide the neural basis of visual masking. We searched for areas whose activity correlated with perception as we systematically varied the strength of masking. A total of 13 subjects performed a backward masking task during functional magnetic resonance imaging. Target and mask were presented at three delay intervals (34, 68, and 102 msec) and behavioral measures confirmed that the targets were more visible at longer masking intervals. Two sets of regions of interest were identified: Distinct regions in the visual cortex (V1/V2, LO, hMT+) were segregated using scans to localize visual processing drawn from the existing literature. Additional cortical regions were selected in a data-driven approach based on their activity during the backward masking task. For each set, we determined the regions whose magnitude of activation increased at longer masking intervals. Nine of the subjects provided valid behavioral performance data on the visual masking task and imaging data from these subjects were used for subsequent analysis. The scans of visual processing areas identified four regions, including: early visual areas (V1 and V2), the motion-sensitive regions in the lateral occipital (LO) lobe (hMT+), and two components (dorsal and ventral) of the object-sensitive region, LO. Of these, the ventral and dorsal LO regions were sensitive to the strength of the mask. For the data-driven approach, six regions were identified on the basis of a difference map in which all masking intervals were contrasted with rest. These included the inferior parietal, anterior cingulate, precentral, insula, thalamic, and occipital areas. The predicted effects of more activity with weaker masking were seen in the thalamus, inferior parietal, and anterior cingulate. This study isolated three types of visual processing areas. The first included regions that subserve key stages of vision (including object and motion processing). The second type responded to the presentation of brief ly presented visual stimuli, regardless of masking interval. The third type (selected from the first two) included regions sensitive to the interval between the target and mask. These latter regions (including ventral LO, inferior parietal, anterior cingulate, and thalamus) may form the neural substrate of backward masking.
在视觉后向掩蔽中，一个短暂呈现的视觉目标的可见性会被随后不久呈现的掩蔽物所干扰。本研究的目的是确定人类皮层中可能为视觉掩蔽提供神经基础的区域。当我们系统地改变掩蔽强度时，我们寻找其活动与感知相关的区域。共有13名受试者在功能磁共振成像期间执行了一项后向掩蔽任务。目标和掩蔽物在三个延迟间隔（34、68和102毫秒）呈现，行为测量结果证实，在较长的掩蔽间隔下目标更易被看见。确定了两组感兴趣区域：利用从现有文献中获取的扫描来定位视觉处理，从而分离出视觉皮层中的不同区域（V1/V2、LO、hMT+）。基于它们在后向掩蔽任务期间的活动，通过数据驱动的方法选择了其他皮层区域。对于每组区域，我们确定了那些激活幅度在较长掩蔽间隔时增加的区域。九名受试者提供了关于视觉掩蔽任务的有效行为表现数据，这些受试者的成像数据用于后续分析。视觉处理区域的扫描确定了四个区域，包括：早期视觉区域（V1和V）、枕叶外侧（LO）叶中的运动敏感区域（hMT+）以及物体敏感区域LO的两个部分（背侧和腹侧）。其中，腹侧和背侧LO区域对掩蔽物的强度敏感。对于数据驱动的方法，基于一个差异图确定了六个区域，在该差异图中所有掩蔽间隔都与静息状态进行了对比。这些区域包括顶下小叶、前扣带回、中央前回、岛叶、丘脑和枕叶区域。在丘脑、顶下小叶和前扣带回中可以看到掩蔽较弱时活动增加的预测效应。本研究分离出了三种类型的视觉处理区域。第一种包括服务于视觉关键阶段的区域（包括物体和运动处理）。第二种类型对短暂呈现的视觉刺激的呈现做出反应，而不考虑掩蔽间隔。第三种类型（从前两种中选择）包括对目标和掩蔽物之间的间隔敏感的区域。这些后一种区域（包括腹侧LO、顶下小叶、前扣带回和丘脑）可能构成后向掩蔽 的神经基础。
