The influence of the place-value structure of the Arabic number ...

INTRODUCTION
The understanding and processing of numerical quantities constitutes one of the most
far reaching steps in the development of numerical cognition. It is not only decisive for
performance in basic numerical tasks such as estimation or number comparison; but also it is
thought to serve as a building block for competences in higher levels of numerical cognition
such as calculation (e.g., Holloway & Ansari, 2008; Laski & Siegler, 2006). Thus, given the
importance of this basic numerical competency, understanding their developmental
trajectories and their cognitive underpinnings seems crucial. However, knowledge on how the
representation of symbolic number magnitude develops and on the factors which determine
this development (e.g., language) is still rather patchy.
The mental number line and its development
It is widely agreed that number magnitude processing operates upon a spatially
organized representation of numbers along a mental number line (MNL; e.g., Dehaene &
Cohen, 1995; Restle, 1970; but see van Opstal, Gevers, de Moor, & Verguts, 2008, for a
different view). Upon this MNL, relatively smaller numbers are associated with the left side,
whereas numbers are represented further and further to the right with increasing magnitude
(e.g., Dehaene, Bossini, & Gireaux, 1993; Zorzi, Priftis, & Umiltà, 2002; Zorzi, Priftis,
Meneghello, Marenzi, & Umiltà, 2006; Priftis, Zorzi, Meneghello, Marenzi, & Umiltà, 2006;
but see Shaki, Fisher, & Petrusic, 2009; Zebian, 2005 for evidence on a reversed orientation
of the mental number line in cultures reading from right to left). Commonly, this spatial
mapping of numbers is thought to develop around the age of 7 (Berch, Foley, Hill, & Ryan,
1999; van Galen, & Reitsma, 2008; but see Opfer, Thompson, & Furlong, in press; Opfer &
Furlong, this issue for evidence suggesting first spatial-numerical associations even in
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