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

to-be-evaluated triplet crossed a decade boundary). These findings again indicated that the
mental number line incorporates structural information on the place-value organization of the
Arabic number system – or as Nuerk, Weger, and Willmes (2001) put it, the existence of
“decade breaks in the mental number line (p. B25).
Further evidence for decomposed processing of tens and units
The results of Studies 1 and 6 were based on tasks for which there is already evidence
suggesting decomposed processing of number magnitude, i.e., the number magnitude
comparison task (e.g., Nuerk et al., 2001; Ratinckx, Nuerk, van Dijk, Willmes, 2006;
Moeller, Fischer, Nuerk, & Willmes, 2009a) and the number bisection task (see Nuerk,
Geppert, van Herten, & Willmes 2002, Moeller, 2006). However, the present thesis also
aimed at gaining further evidence for the importance of structural place-value information
from tasks previously not primarily considered to be sensitive to place-value related
influences. At the level of basic arithmetic operations, i.e., addition, it was observed that the
need of a carry operation (requiring specific processes of place-value integration, e.g., 36 +
48) specifically increased processing demands on the unit digits of the summands. Moreover,
as observed in Study 4 of the current thesis it seems that children’s performance in number
line estimation tasks is accounted for best by a model suggesting two separate representations
of single- and two-digit numbers. Thereby, the results again indicated that place-value
attributes of the Arabic number system are retained in the human representation of numerical
magnitude.
Longitudinal developmental aspects of place-value understanding
The preceding paragraphs were aimed at establishing decomposed processing of multidigit
numbers as a general processing principle. Additionally, first evidence for influences of
children’s place-value knowledge on numerical development was described (cf. Study 4).
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