Six-month-old infants discriminate between large sets of objects on the basis of numerosity when other extraneous variables are controlled, provided that the sets to be discriminated differ by a large ratio (8 vs. 16 but not 8 vs. 12). The capacities to represent approximate numerosity found in adult animals and humans evidently develop in human infants prior to language and symbolic counting.

Human beings are permanently required to process the world numerically and, consequently, to perform computations to adapt their behaviour and they have developed various calculation strategies, some of them based on specific manipulations of the fingers. In this chapter, we argue that the way we express physically numerical concepts by raising fingers while counting leads to embodied representations of numbers and calculation procedures in the adult brain. To illustrate this, we focus on number and finger interactions in the context of (...) simple arithmetic operations. We show that the fixed order of fingers on the hand provides human beings with unique facilities to increment numerical changes or represent a cardinal value while solving arithmetic problems. In order to specify the influence of finger representation on mental arithmetic both at the cognitive and neural level, we review past and recent findings from behavioural, electrophysiological, and brain imaging studies. We start with anthropological and developmental data showing the role of fingers in the acquisition of arithmetic knowledge, then address the issue of whether number and finger interactions are also observed in adults solving arithmetic problems mentally. We suggest that arithmetic performance depends on the integrity of finger representations in children and adults. Finally, we overview the results of recent functional magnetic resonance imaging studies showing a common brain substrate for finger and number representations during and after the acquisition of arithmetic skills. (shrink)