Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Daniel Ansari


Developmental dyscalculia (DD) is a specific learning disorder of calculation abilities. In the present thesis I report a series behavioural and functional neuroimaging studies to further elucidate the core numerical deficits underlying DD. I recruited a sample of children with DD who demonstrated persistent impairments in arithmetic. In Chapter 2, to validate the selection criteria, I compared the performance of children with and without persistent DD on a test of numerical magnitude processing. The data showed that only children with persistent DD presented with deficits in numerical magnitude processing, while those with inconsistent DD perform at the level of age-matched typically developing (TD) controls.

In Chapter 3, I compared the performance of children with persistent DD on tasks assessing symbolic (e.g. Arabic digits) and non-symbolic (e.g. dot arrays) processing skills. Children with DD performed significantly worse on symbolic but not non-symbolic numerical magnitude processing tasks. These findings suggest that DD arises not from a format-independent magnitude processing deficit, but rather from difficulties in processing symbolic number representations.

In Chapter 4, I investigated the influence of non-numerical variables (e.g. size) on non-symbolic numerical magnitude processing in children with and without DD. Children with DD were found to exhibit deficits in non-symbolic processing only when the visual perceptual cues were anticorrelated with numerical magnitude. When numerical magnitude and area were congruent no group differences in performance emerged. Therefore, rather than presenting with a core deficit in non-symbolic processing, children with DD have difficulties in disentangling numerical and non-numerical cues.

In Chapter 5, I used functional neuroimaging to investigate whether children with DD exhibit atypical brain activation during numerical magnitude processing (symbolic, non-symbolic and mixed comparison). The data from this study revealed atypical cortical activity in the Intraparietal Sulcus (IPS) during symbolic and mixed format (comparing symbolic with non-symbolic) tasks. In contrast, children with DD did not exhibit differences in the IPS during non-symbolic numerical magnitude processing. These neuroimaging findings complement the behavioral data in Chapter 3 and 4 by suggesting that children with DD have a deficit in semantic representation of symbolic numerical magnitudes rather than a core deficit in representing both symbolic and non-symbolic numerical magnitudes. The findings from these studies provide converging evidence to support a core deficit in processing the semantic meaning of symbolic numerals in children with persistent DD.