The representation of ordinal information: domain specific or domain general ?

Ordinal processing involves processing of the sequential relations between stimuli of a stimulus set. This crucial ability has been studied extensively and separately in different domains such as working memory (WM) and numerical cognition. Several behavioural and neuroimaging studies suggest the possibility of common ordinal coding mechanisms across different domains. This fMRI study assessed the hypothesis of common ordinal representational mechanisms across the WM, the number and the letter domains. We administered three ordinal judgement tasks (for alphabetical, numerical, and verbal WM judgment) with further manipulation of ordinal distance, and a luminance judgment control task. Our results demonstrated between-task predictions of ordinal distance in fronto-parietal cortices were robust between serial order WM, alphabetical order judgment tasks as well as a luminance judgment control task but not when involving the numerical order judgment tasks. They suggest that common neural substrates characterize processing of ordinal information in WM and alphabetical but not numerical domains. Moreover, additional results suggest that the commonality may reflect attentional control processes involved in judging ordinal distances rather than the intervention of domain-general ordinal codes.