Dipartimento di Psicologia Generale, Università di Padova, Padova, Italy.
Neuroimage. 2011 May 15;56(2):674-80. doi: 10.1016/j.neuroimage.2010.06.035. Epub 2010 Jun 19.
Neuroimaging studies of numerical cognition have pointed to the horizontal segment of the intraparietal sulcus (hIPS) as the neural correlate of numerical representations in humans. However, the specificity of hIPS for numbers remains controversial. For example, its activation during numerical comparison cannot be distinguished from activation during ordinal judgments on non-numerical sequences such as letters (Fias et al., 2007, J. Neuroscience). Based on the hypothesis that the fine-grained distinction between representations of numerical vs. letter order in hIPS might simply be invisible to conventional fMRI data analysis, we used support vector machines (SVM) to reanalyse the data of Fias et al. (2007). We show that classifiers trained on hIPS voxels can discriminate between number comparison and letter comparison, even though the two tasks produce the same metric of behaviour. Voxels discriminating between the two conditions were consistent across subjects and contribution analysis revealed maps of distinct sets of voxels implicated in the processing of numerical vs. alphabetical order in bilateral hIPS. These results reconcile the neuroimaging data with the neuropsychological evidence suggesting dissociations between numbers and other non-numerical ordered sequences, and demonstrate that multivariate analyses are fundamental to address fine-grained theoretical issues with fMRI studies.
神经影像学研究表明，人类的数字认知与顶内沟的水平段（hIPS）有关。然而，hIPS 对数字的特异性仍然存在争议。例如，在对非数字序列（如字母）进行序数判断时，其激活不能与数字比较期间的激活区分开来（Fias 等人，2007 年，《神经科学杂志》）。基于这样的假设，即 hIPS 中数字与字母顺序表示之间的细微区别可能根本无法通过常规 fMRI 数据分析来识别，我们使用支持向量机（SVM）重新分析了 Fias 等人（2007 年）的数据。我们表明，在 hIPS 体素上训练的分类器可以区分数字比较和字母比较，尽管这两个任务产生了相同的行为度量。在不同的受试者中，区分这两种条件的体素是一致的，并且贡献分析揭示了双侧 hIPS 中涉及数字与字母顺序处理的不同体素集的映射。这些结果将神经影像学数据与神经心理学证据相协调，表明数字和其他非数字有序序列之间存在分离，并证明多元分析对于解决 fMRI 研究中的细粒度理论问题至关重要。
