University of Chicago, Chicago, Illinois 60637, and Department of Psychology, University of Western Ontario, London, Ontario N6A 3K7, Canada.
J Neurosci. 2013 Oct 23;33(43):17052-61. doi: 10.1523/JNEUROSCI.1775-13.2013.
The view that representations of symbolic and nonsymbolic numbers are closely tied to one another is widespread. However, the link between symbolic and nonsymbolic numbers is almost always inferred from cardinal processing tasks. In the current work, we show that considering ordinality instead points to striking differences between symbolic and nonsymbolic numbers. Human behavioral and neural data show that ordinal processing of symbolic numbers (Are three Indo-Arabic numerals in numerical order?) is distinct from symbolic cardinal processing (Which of two numerals represents the greater quantity?) and nonsymbolic number processing (ordinal and cardinal judgments of dot-arrays). Behaviorally, distance-effects were reversed when assessing ordinality in symbolic numbers, but canonical distance-effects were observed for cardinal judgments of symbolic numbers and all nonsymbolic judgments. At the neural level, symbolic number-ordering was the only numerical task that did not show number-specific activity (greater than control) in the intraparietal sulcus. Only activity in left premotor cortex was specifically associated with symbolic number-ordering. For nonsymbolic numbers, activation in cognitive-control areas during ordinal processing and a high degree of overlap between ordinal and cardinal processing networks indicate that nonsymbolic ordinality is assessed via iterative cardinality judgments. This contrasts with a striking lack of neural overlap between ordinal and cardinal judgments anywhere in the brain for symbolic numbers, suggesting that symbolic number processing varies substantially with computational context. Ordinal processing sheds light on key differences between symbolic and nonsymbolic number processing both behaviorally and in the brain. Ordinality may prove important for understanding the power of representing numbers symbolically.
符号和非符号数字之间的表示紧密相关的观点是广泛存在的。然而，符号和非符号数字之间的联系几乎总是从基数处理任务中推断出来的。在当前的工作中，我们表明，考虑顺序性会指向符号和非符号数字之间的显著差异。人类行为和神经数据表明，符号数字的顺序处理（三个印度-阿拉伯数字是否按数字顺序排列？）与符号基数处理（两个数字中哪一个表示更大的数量？）和非符号数字处理（点数组的顺序和基数判断）不同。行为上，在评估符号数字的顺序性时，距离效应被反转，但在符号数字的基数判断和所有非符号判断中都观察到了典型的距离效应。在神经水平上，符号数字排序是唯一一项在顶内沟中没有表现出数字特异性活动（大于控制）的数值任务。只有左前运动皮层的活动与符号数字排序特异性相关。对于非符号数字，在顺序处理期间认知控制区域的激活以及顺序和基数处理网络之间的高度重叠表明，非符号顺序性是通过迭代基数判断来评估的。这与符号数字在大脑中任何地方的顺序和基数判断之间都没有明显的神经重叠形成鲜明对比，这表明符号数字处理在很大程度上取决于计算上下文。顺序处理揭示了符号和非符号数字处理在行为和大脑中的关键差异。顺序性可能对理解符号表示数字的能力很重要。
