Among individuals with dyscalculia, prevalence rates for other developmental problems are clearly higher than in the general population. Comorbidity itself therefore constitutes a central characteristic of dyscalculia. Thus, research designs are needed which explicitly account for comorbid problems in order to examine the specificity of any risk or protective factor. Multiple-deficit models seem best suited to explain the heterogeneity of dyscalculia. Numerical processing is proposed as a core deficit associated with problems in arithmetic skills. Individual manifestations of dyscalculia, however, arise from a complex interplay of deficits in numerical processing with other neurobiological, cognitive and environmental factors. The exact nature of these interactions has yet to be determined. Implications of multiple-deficit models for research and clinical practice are discussed.
- Multiple-deficit model