Sensori-motor skills were first linked to arithmetic via Gerstmann’s syndrome, which is argued to be a cluster of symptoms involving skills relying on the integration of motor and sensory skills (Lebrun, 2005). There are two dominant theories attempting to explain the co-occurrence of these symptoms; a functional account and localizationist account. In the functional account, theorists propose that finger awareness (a sensori-motor skill) and arithmetic are related due to the role of using fingers in counting and addition and subtraction (Butterworth, 1999). In this account, finger awareness would be better correlated with counting and arithmetic than other sensori-motor skills. Alternatively, the localizationist account proposes that sensori- motor skills and other symptoms of Gerstmann’s syndrome are correlated with
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arithmetic due to the proximity of brain regions associated with these skills (e.g. Dehaene, Piazza, Pinel, & Cohen, 2003). In this account, any sensori-motor ability relying on the parietal lobe will be related to numerical and calculation abilities. We aimed to assess these theories by including finger gnosis and sensori-motor skills including graphisthesia (argued to rely on the parietal lobe) and left-right orientation (a Gerstmann’s syndrome). Previous studies have not included all three factors within one design. Moreover, finger gnosis tasks used in previous studies have shown low reliability (Noël, 2005; Wasner et al., 2016) and one study examining graphisthesia included verbal and numerical information within it. Our study used a reliable finger gnosis task (Cronbach’s alpha = .74), removed verbal and numerical confounds in the graphisthesia task, and included other Gerstmann syndrome tasks to directly compare the relationship between these measures.
In our study, we found no evidence to support a functional account and limited evidence to support a localizationist account. The three skills were moderately and significantly correlated with arithmetic (rs = .34-.43) but these were reduced to a weak correlation after age was controlled for left-right orientation and graphisthesia (rs = .29; .25, respectively) and non-significant and negligible correlation with finger gnosis (r = .12, p < .05). Moreover, regression analyses showed that graphisthesia does not play a unique role in predicting arithmetic once other important factors (age, counting and symbolic number comparison) are included, and left-right orientation is a weak correlate of arithmetic.
All three skills were entered into the model and only left-right orientation remained a significant predictor, explaining an additional 2% of the variation in arithmetic. Importantly, our counting and comparison tasks showed good reliability and a good range of scores, and the finding that these exact skills are important predictors of arithmetic is in line with previous evidence (see Section 2.2.1). This suggests that our study is well placed to find a relationship between sensori-motor skills and arithmetic, should one exist, and therefore we argue that there is limited evidence to support either a functional or localizationist account of the relationship between sensori-motor skills and arithmetic development.
We found that left-right orientation remained a significant unique predictor of arithmetic after controlling for exact number abilities (R2 = .20). Although this is a
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small and likely clinically insignificant effect, it is worth considering what this means in regard to the localizationist theory. This theory proposes that skills relying on the parietal lobe, for instance Gerstmann symptoms, will predict arithmetic which also relies on the parietal lobe (see Dehaene et al., 2003). However, we found that the correlations between left-right orientation and finger gnosis and graphisthesia, also proposed to rely on the parietal lobe (Fayol et al., 1998; Noël, 2005) were weak. We tentatively suggest that it is possible that verbal abilities may explain in part the correlations seen between left-right orientation and arithmetic, as both of these rely on verbal abilities (Durand et al., 2005). The left-right orientation task involved considerable verbal information, whereas the graphisthesia task (point to objects) and the finger gnosis task (point to fingers) required less verbal information. However, we found weak relationships between the sensori-motor skills and vocabulary once age was controlled (although vocabulary was moderately and significantly correlated with arithmetic; partial r = .24). Further research should consider including spatial awareness and non-verbal IQ measures to assess why such a relationship may exist. We suggest that previous evidence which supports a relationship between finger gnosis and other sensori-motor skills is limited, explaining the difference in findings from some previous studies and our study. For example, Noël (2005) fails to account for the effect of age in a study which had variation within ages of the children and therefore likely over estimates the correlation between finger gnosis and left-right orientation. Our study highlights the importance of including age as a control measure due to the significant correlation with arithmetic (age explained 35% of the unique variation in arithmetic scores). Gracia-Bafalluy and Noël (2008) report a significant improvement in arithmetic scores after finger gnosis training, although this study had a small sample size (N = 33) and no baseline scores for the groups were reported (see Fischer, 2010). Fayol et al. (1998) report a relationship between a composite score of sensori-motor skills including graphisthesia and finger gnosis. However, this battery included some numerical processing which may have confounded the results, and the arithmetic measure was a composite of numerical tasks including approximate number abilities and complex verbal addition tasks (e.g. “Jack has 6 green pencils, 4 red pencils and 5 blue pencils. How many pencils has he got?” p. 66). Moreover, when the “pure” arithmetic task (addition and subtraction scores) was compared to the
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neuropsychological composite score, the relationship with arithmetic was far weaker than it was to the numerical composite.
More recent evidence, which has overcome such limitations, fails to report a significant and important relationship between finger gnosis and arithmetic. For example, Wasner et al. (2016) showed that finger gnosis explained 1-2% of the variation in arithmetic (N = 321) after controlling for age, number skills and memory; the same level we showed. Penner-Wilger et al. (2007) showed that finger gnosis and arithmetic was weakly correlated (r = .16, N = 146) which is equivalent to the correlation we found between finger gnosis and arithmetic. Similarly, Newman (2016) found no evidence for a correlation in a sample of 76 children once age was controlled. None of these studies have examined how sensori-motor skills, other than finger gnosis, relate to arithmetic and therefore we are the first to show that neither finger gnosis, nor other sensori-motor skills, appear to play an important role in arithmetic development.