Article summary with No evidence for a core deficit in developmental dyscalculia or mathematical learning disabilities by Mammarella a.o. - 2021

What is a mathematical learning disability (MLD)?

The DSM-5 defines mathematical learning disability (MLD) as a specific learning disorder with impairment in mathematics. To diagnose MLD, psychometric cut-offs should be met as well as the other criteria (for example the persistence of symptoms for at least six months despite specific interventions targeting the issue). Performing bad in math at one moment in time does not necessarily mean that a child has MLD.

What are the two main hypotheses with regards to developmental dyscalculia?

The literature has been dominated by two hypotheses:

• The core deficit hypothesis of domain-specific numerical acuity, magnitude representation or number sense.
• The domain-general hypothesis assumes that cognitive impairments in attention, working memory, short-term memory, or executive functions contribute to explaining mathematical difficulties. 

How are these two hypotheses used in this study to test differences between typically-developing children and those with MLD?

Based on the two main hypotheses of developmental dyscalculia two hypotheses were tested in this study:

• Dimensional hypothesis: Do differences between typically-developing children and those with MLD reflect global characteristics of the population considered as a whole?
• Core deficit hypothesis: Is the MLD group characterized by core deficits that cannot be inferred from the global parameters that describe the rest of the population?

Does a mathematical learning disability coincide with a core deficit in cognitive skills?

None of the measures of basic number processing or domain-general abilities identified core deficits in children with MLD. All the differences between MLD and control groups reflected the global characteristics of the sample population. Discrepancy between the MLD and the control group was the largest in symbolic magnitude comparison accuracy and in working memory measures (especially verbal working memory).

Why is looking for a core deficit in children with MLD simplistic?

Children with MLD may have deficits in both basic number processing and domain-general cognitive skills, but neither of these are necessarily present. Also, math performance may correlate differently with various basic number processing and domain-general measures in the general population. The cognitive profile then seen in MLD could just be a reflection of this set of correlations after specific psychometric selection criteria have been applied.

How can research into the core deficit hypothesis and the domain-general hypothesis be improved?

Children should be positioned in a multi-dimensional measurement space that includes both domain-general and domain-specific measures. In a multi-dimensional space, children with MLD should occupy different moderate to extreme positions, without the abrupt changes that are predicted by core deficit models. This also lends the opportunity for further investigating other moderating factors, such as comorbidity, age, and severity of the disorder.