Guo Bingbing, Meng Ming
Dartmouth College, Department of Psychological and Brain Sciences, 6207 Moore Hall, Hanover, NH 03755, USA.
Dartmouth College, Department of Psychological and Brain Sciences, 6207 Moore Hall, Hanover, NH 03755, USA.
Neuroimage. 2015 Aug 1;116:240-7. doi: 10.1016/j.neuroimage.2015.04.006. Epub 2015 Apr 11.
Several brain areas in the inferior temporal (IT) cortex, such as the fusiform face area (FFA) and parahippocampal place area (PPA), are hypothesized to be selectively responsive to a particular category of visual objects. However, how category-specific and nonspecific information may be encoded at this level of visual processing is still unclear. Using fMRI, we compared averaged BOLD activity as well as multi-voxel activation patterns in the FFA and PPA corresponding to high-contrast and low-contrast face and house images. The averaged BOLD activity in the FFA and PPA was modulated by the image contrast regardless of the stimulus category. Interestingly, unlike the univariate averaged BOLD activity, multi-voxel activation patterns in the FFA and PPA were barely affected by variations in stimulus contrast. In both the FFA and PPA, decoding the categorical information about whether participants saw faces or houses was independent of stimulus contrast. Moreover, the multivariate pattern analysis (MVPA) results were highly stable when either the voxels that were more sensitive to stimulus contrast or the voxels that were less sensitive were used. Taken together, these findings demonstrate that both category-specific (face versus house) information and nonspecific (image contrast) information are available to be decoded orthogonally in the same brain areas (FFA and PPA), suggesting that complementary neural mechanisms for processing visual features and categorical information may occur in the same brain areas but respectively be revealed by averaged activity and multi-voxel activation patterns. Whereas stimulus strength, such as contrast, modulates overall activity amplitudes in these brain areas, activity patterns across populations of neurons appear to underlie the representation of object category.
颞下回（IT）皮质中的几个脑区，如梭状面孔区（FFA）和海马旁位置区（PPA），被认为对特定类别的视觉对象具有选择性反应。然而，在这个视觉处理水平上，类别特异性和非特异性信息是如何编码的仍不清楚。我们使用功能磁共振成像（fMRI），比较了FFA和PPA中对应于高对比度和低对比度面部及房屋图像的平均血氧水平依赖（BOLD）活动以及多体素激活模式。FFA和PPA中的平均BOLD活动受到图像对比度的调制，而与刺激类别无关。有趣的是，与单变量平均BOLD活动不同，FFA和PPA中的多体素激活模式几乎不受刺激对比度变化的影响。在FFA和PPA中，解码参与者看到的是面孔还是房屋的类别信息均与刺激对比度无关。此外，当使用对刺激对比度更敏感或较不敏感的体素时，多变量模式分析（MVPA）结果都高度稳定。综上所述，这些发现表明，类别特异性（面孔与房屋）信息和非特异性（图像对比度）信息在同一脑区（FFA和PPA）中均可被正交解码，这表明处理视觉特征和类别信息的互补神经机制可能发生在同一脑区，但分别由平均活动和多体素激活模式揭示。虽然刺激强度，如对比度，会调制这些脑区的整体活动幅度，但神经元群体的活动模式似乎是对象类别的表征基础。
