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

manipulations cannot be distinguished from more general processes (e.g. response selection,
see Goebel et al., 2004). In these cases, differences in brain activation patterns associated with
either procedural or fact knowledge, or magnitude representations cannot definitely be
attributed to the critical involvement of these constructs, but also to task requirements and
stimuli used. Therefore, employing a within-task approach instead of a between-task approach
to examine the interactions between procedural and fact knowledge, as well as magnitude
representation would be desirable.
Addressing this issue, Nuerk, Geppert, van Herten, and Willmes (2002) presented a
modified version of the number bisection task (NBT) as initially used by Dehaene and Cohen
(1997) to assess spared numerical abilities in an acalculic patient. In Nuerk et al.’s (2002)
verification version of the NBT, healthy adult participants were to determine whether the
central number of a triplet also represents the arithmetic mean of the interval (e.g. 23_25_27)
or not (e.g. 23_25_29; see also Hoeckner et al., 2008 for results in hemineglect patients). As
performance in the NBT is supposed to rely exclusively on magnitude manipulations, the
NBT is commonly used to assess number magnitude representation (Cohen et al., 2000;
Dehaene and Cohen, 1997). However, Nuerk et al. (2002) showed that different number
representations specifically influenced speed and accuracy in the NBT. In their factorial
design, Nuerk et al. (2002) identified multiplicativity (i.e. whether or not a triplet was part of
a multiplication table) and bisection range (i.e. distance between the outer numbers) to be the
most important predictors of performance for correctly bisected triplets. Whereas for triplets
not correctly bisected, distance from the central number to the arithmetic mean of the interval
and bisection possibility (i.e. whether or not the interval can be bisected by an integer)
reliably predicted behavioural performance.
Additionally, Nuerk and colleagues (2002) conducted a regression analysis on item RT
to investigate the impact of item properties not manipulated in their stimulus set. Thereby,
decade crossing and measures of problem size were identified to generally influence
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