Are numbers special? Comparing the generation of verbal materials from ordered categories (months) to numbers and other categories (animals) in an fMRI study

Abstract

Months, days of the week, and numbers differ from other verbal concepts because they are ordered in a sequence, whereas no order is imposed on members of other categories, such as animals or tools. Recent studies suggest that numbers activate a representation of their quantity within the intraparietal sulcus (IPS) automatically, that is, in tasks that do not require the processing of quantity. It is unclear, however, whether ordered verbal materials in general and not only numbers activate the IPS in such tasks. In the present functional magnetic resonance imaging study word generation of months, numbers, and animals were compared. Word generation of numbers and nonnumerical materials from an ordered category (months) activated the IPS more strongly than generating items from a not-ordered category such as animals or the verbal control conditions. An ROI analysis of three subregions within the anterior IPS revealed that the most anterior and lateral of these regions, human intraparietal area hIP2, shows a greater sensitivity to ordered materials than the other two areas, hIP1 and hIP3. Interestingly, no difference in activation was observed within the IPS between numbers and months suggesting that the activation of the IPS might not be modulated by the additional quantity information carried by numbers.

Distinct representations of numerical and non-numerical order in the human intraparietal sulcus revealed by multivariate pattern recognition

“…It is worth noting that Eger et al (2003) found stronger activation of hIPS for number processing than for letter processing but their simple identification task did not involve processing the ordinal dimension of letters. Further support to the hypothesis that hIPS is involved in the representation and processing of non-numerical ordered sequences (Fias et al, 2007) is provided by the study of Ischebeck et al (2008), who found no significant difference in IPS between ordered generation of months and numbers, compared to the generation of non-ordered names of animals.…”

“…However, there is a third possible interpretation. The results of Fias et al (2007) and Ischebeck et al (2008), though suggestive, do not necessarily imply that the same neuronal populations within hIPS are involved in processing both numerical and non-numerical ordered sequences (see Jacob and Nieder, 2008, for a similar argument). The results might be an artefact due to the limited spatial resolution of fMRI and/or the limitations imposed by the conventional univariate fMRI data analysis (general linear model).…”

“…In summary, the fact that hIPS activation during number comparison cannot be distinguished from activation during comparison of non-numerical ordered sequences can be interpreted in two ways: either hIPS is coding abstract order information, common to all ordered sequences (Fias et al, 2007;Ischebeck et al, 2008), or hIPS activation reflects a shared comparison mechanism that operates on any type of conceptual information (Cappelletti et al, 2010). However, there is a third possible interpretation.…”

When time is space: Evidence for a mental time line

“…It should be noted that the specificity of hIPS for numerical processing has been criticized by some authors, who found similar patterns of activation while processing numerical and nonnumerical ordered sequences (Fias et al, 2007;Ischebeck et al, 2008), as if hIPS activation in tasks that involve the processing of numerical magnitude would be induced by the ordinal (rather than cardinal) dimension. This raises again the question of whether ordinality might be the common feature subtending the similarity between number and time and whether time is processed in the same network devoted to numbers.…”

Revisiting von Restorff’s early isolation effect

“…Digits are both visually and conceptually different from verbal materials. Brain-imaging studies have shown that processing numbers and other ordered categories (e.g., months) engages a different part of the brain than processing conceptual categories (e.g., animals; see Ischebeck et al, 2008). Young children failed to show a midlist isolation effect with digits isolated in a series of pictures (Howe, Courage, Vernescu, & Hunt, 2000).…”