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

Until now, research about developmental dyscalculia and mathematical disabilities (MLD) have been based on two hypotheses:

1. The core deficit hypothesis of domain-specific numerical acuity, magnitude representation or number sense, which suggests that a specific impairment in numerical processing is the underlying cause of dyscalculia.

2. The domain general hypothesis, which proposes that cognitive deficits in areas like attention, memory, and executive functions contribute to mathematical difficulties.

However, there is no general consensus on the definition of MLD and the criteria for diagnosis. This study contributes to the discussion by comparing standardized differences between observed MLD cases and a control group, using a simulation. In this way, the researchers aim to answer the question whether there is a core deficit in MLD. First, the  challenges in diagnosing and defining MLD are explained. Finally, the results from the study will be discussed.

How is MLD defined?

The DSM-5 defines MLD as a specific learning disorder with impairment in mathematics. They adopted a dimensional approach, but still allow for the identification of the specific learning domains affected in MLD. According to the criteria set forth in the DSM-5, individuals can be diagnosed with a specific learning disorder, such as MLD, if they exhibit symptoms of the corresponding impairments for a minimum of six months, even after targeted interventions have been employed to address their difficulties. Specific learning disorders typically manifest in children with average intellectual abilities and result in lifelong challenges in activities that depend on certain learning skills.

How did the researchers test the hypothesis?

The children in the study were assessed at their school in three separate sessions that took place from January to May. The testing involved both group sessions and individual sessions. Group sessions were used for the fluid intelligence task and certain Math achievement subtests, and the order of test administration varied across classes. In the math achievement subtests, the mathematical abilities were tested with different subtests. The fluid intelligence test measured non-verbal reasoning. Following the group session, two individual sessions were conducted, each lasting about 50 minutes. These individual sessions included tasks related to reading, math tasks, and computerized tasks. Both paper-and-pencil and computerized tasks were evenly distributed and counterbalanced across the two individual sessions. 

Can we identify core deficits in children with MLD? 

The results of these tests supported the domain general hypothesis. The researchers did not find any core deficits, but rather a reflection of the global characteristics of the sampled population. This implies that children with MLD may have deficits in basic number processing or domain general skills, but these deficits are not present in all cases and therefore do not form core deficits. 

A limitation of the study is the large sample population and the usage of widely accepted criteria. Testing with children with a clinical diagnosis, using clinical diagnosis criteria, may lead to a more certain conclusion about the presence of core deficits. In further research, it is recommended to use a dimensional approach to study MLD and to explore comorbidities and changes in symptoms over time.