The nature of order processing deficits in developmental dyscalculia: The influences of familiarity and the count-list

Children with developmental dyscalculia often show impaired performance on number order processing tasks. Recent findings suggest these deficits are not general in nature, but instead specific to certain kinds of sequences. In particular, one proposal is that dyscalculic children struggle specifically to understand that “in order” can refer to sequences outside of the (ascending-consecutive) count-list (e.g., 1-3-5 is in order). However, previous findings in support of this view were limited by (i) only considering ascending sequences and (ii) not accounting for other factors known to influence order processing performance, such as sequence familiarity. To address this, the present study compared a control ( n = 28) and dyscalculic group ( n = 12), aged between 7-12 years, across ascending and descending sequences varying in familiarity. As expected, dyscalculic children showed impaired performance on ascending non-consecutive sequences (e.g., 1-3-5) but not on ascending consecutive sequences (e.g., 1-2-3). Notably, however, this deficit appeared to remain only for unfamiliar sequences (e.g., 2-5-8) and not familiar ones (e.g., 2-4-6), although this interaction was non-significant. Moreover, dyscalculic children displayed typical performance across both consecutive (e.g., 5-4-3) and non-consecutive (e.g., 5-3-1) descending sequences, neither of which match the traditional count-list. Accordingly, although order processing deficits in developmental dyscalculia do appear specific in nature, they are not necessarily specific to non-count-list sequences.