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Understanding Dyscalculia, Dyslexia’s Numeric Counterpart

Experts estimate that 3 to 7 percent of the global population has developmental dyscalculia, though it often goes undiagnosed. The disorder may be poorly understood, but it is very real—and so are its consequences.

Dyscalculia, which is classified as a specific learning disorder in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5), typically appears in childhood and affects a person’s ability to understand math and number-based information because their brain doesn’t process math-related concepts in the same way as those without the disorder, but they are no less intelligent.

Though dyscalculia is defined in the DSM-5 and accepted as a disorder, a lack of research has left many unanswered questions about its causes and treatment. People with dyscalculia often struggle with transitive inference—a form of deductive reasoning used to derive a relation between items. (If item A is larger than item B and item B is larger than item C, then item A is larger than item C.)

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They may also have trouble keeping track of time, distinguishing left from right and following sequential instructions, so they may struggle to drive a car, follow a recipe or learn dance steps. And they may have difficulty with putting sequences such as everyday familiar events in order.

It’s common for people with dyscalculia to also have mental health disorders, including anxiety and panic disorders and depression, as well as other neurodivergent conditions, such as attention deficit hyperactivity disorder, sensory processing disorder, autism spectrum disorder and dyslexia. Although dyslexia, difficulty with reading, is also classified as a specific learning disorder, it is much more widely known and remains less of a mystery than dyscalculia.

According to a 2018 study co-authored by Kinga Morsanyi, a senior lecturer in mathematical cognition at Loughborough University in England, a child with dyslexia is 100 times more likely to be diagnosed and given support than a child with dyscalculia. There are many reasons for this, including that dyscalculia is far less understood than dyslexia by educators and researchers (among whom there is no agreed-upon criteria that will inform diagnosis). To date, research is inconclusive, and there’s a debate around whether number blindness or number perception is at the root of the disorder.

Dyscalculia has neither one definitive cause nor one single set of symptoms, and the studies exploring the causes have yielded conflicting results. Further, dyscalculia research, scientists say, lags far behind dyslexia research, in part because of a lack of awareness and funding and also because math (beyond the very basic level) is not prioritized as much as reading.

“In our society, there’s an assumption that some people are math people and others aren’t,” but we don’t assume the same for reading, says Daniel Ansari, a professor of developmental cognitive neuroscience and head of the Numerical Cognition Laboratory at Western University in Ontario. “We need the same attitude when it comes to math,” he says.

Ansari says that many dyscalculia studies, including some of his own, are underpowered and have very small sample sizes. The way dyscalculia is defined in research studies also varies substantially, and some researchers find the DSM-5 definition too narrow.

While acknowledging that being able to label learning disorders is necessary for allocating resources to students, Ansari says it’s important to think about them as a continuum. “From a research point of view, looking at the overlap between difficulties is much more interesting than trying to create these separate categories,” he says.

Similarly, Gavin Price, an associate professor of psychology at the University of Exeter in England, who has published numerous studies with Ansari, asserts that views on the causes of dyscalculia vary: “There’s no consensus view. There’s no consensus diagnostic approach or criteria,” he says, and the studies that have been conducted show conflicting results.

Another factor contributing to the mystery is the complexity of math. Morsanyi points out that children typically learn to read within a few months, and once they have, that skill is mastered. If one wants to master math, however, the process is longer. Each skill level builds upon the previous one—multiplication and division build upon addition and subtraction—and there are many more levels of explicit skill knowledge in math than in reading.

“Part of the reason there’s such a challenge about dyscalculia and understanding the condition is that we haven’t had a good understanding of the skills we need when we’re learning math,” explains Camilla Gilmore, a professor of mathematical cognition at Loughborough University.

The true challenge of understanding dyscalculia, Price contends, has to do with the fact that it is a very heterogeneous disorder. “There’s a staggering complexity to dyscalculia, and if somebody is bad at math, there are thousands of pathways to that point,” Price says.

Currently a big debate persists in the field around whether dyscalculia is rooted in an innate disorder of number perception (an ability to readily estimate the number of objects) or number blindness (an inability to recognize numerical symbols and to connect them to the quantities they represent). The largest study to date, which included 1,303 children, points toward number blindness as the cause.

Regardless of whether number blindness or number perception is the root cause of dyscalculia, a large body of research has identified other cognitive skills integral to a person’s ability to do math.

Price says there used to be an emphasis on the importance of domain-specific mathematical skills, such as understanding and comparing numbers, being able to match numbers and quantities, and counting and retrieving number facts (simple addition, subtraction, multiplication or division of two numbers). But over the past five to 10 years, researchers have started to focus on how these numerical systems interact with domain-general cognitive skills, cognitive abilities that are not specific to math, such as executive function and memory.

This is where it gets even more complicated, Gilmore says, because the distinction between domain-specific and domain-general skills is not as clear-cut as once thought. “Although we can distinguish between the two, domain-general skills might be more context-based, so you might be good at them in a particular domain compared to other domains.”

A person may be good at holding nonnumerical information such as words in mind but have difficulty remembering numbers, for example. Or one could have difficulty focusing attention on numerical information but have no trouble focusing in another context, such as reading.

This leads to the critical contribution of executive function skills, which enable one to focus attention, remember instructions, control thought and juggle multiple tasks successfully.

For example, Gilmore and others have done research pointing to the importance of being able to exert inhibitory control, one aspect of executive function that relates to suppressing distracting information and unwanted responses when doing math. For example, a person must ignore colors when asked to add three sets of objects that are different colors.

Understanding dyscalculia is further complicated because doing math involves logic as well as numbers, and there are multiple studies that document a relationship between nonnumerical as well as numerical ordering performance and math skills. In 2018 Morsanyi co-authored a study that found children’s nonnumerical ordering ability in their first year of school was the strongest longitudinal predictor of math abilities one year later.

In December 2023 she co-authored another study in which children between the ages of four and five were trained on number ordering, daily event ordering and order working memory (in this case, the ability to re-create the correct sequence of a list of animals) during a three-week period. Math skills and math anxiety were measured before and after the training.

“We found that if you train children in processing skills, they get better at doing math,” Morsanyi says. “So this would be evidence that ordered processing forms the basis of mathematics—not the only basis of mathematics, because it’s very complicated, but a very important building block.”

To further complicate matters, there are numerous difficulties associated with dyscalculia, but not everyone experiences every difficulty, which means that there’s an immense number of variables to consider when researching the condition.

The mystery of dyscalculia will eventually be solved, researchers believe. They emphasize, however, that there must be a standard definition and more research with bigger sample sizes.

Price describes the current research landscape as patchy and inconsistent. “How do we study it if we don’t have a good definition or diagnosis, and how do we get that definition or diagnosis if we can’t study it accurately?” he asks.

Ansari also advocates for following in the footsteps of genomic researchers and establishing research consortiums that require that investigators around the world follow the same protocol.

“I feel confident that we are already making progress toward understanding dyscalculia and especially building awareness,” Ansari says. “In the end, it’s all about the children who are affected by it.”


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