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

affected (e.g. Dehaene & Cohen, 1997; Delazer et al., 2006, but see Ashkenazi, Henik,
Ifergane, & Shelef, this issue for differing results). However, the left IPS was preserved in our
neglect patients as they all had right-hemispheric lesions. Thus, this left IPS area might have
compensated for the loss of the right IPS with regard to general magnitude and numerical
distance processing.
Nuerk et al. (2005) employed a magnitude comparison task in an Eriksen flanker
paradigm. They found that the magnitude of the distractors was processed. However, the
magnitude of the distractors was not spatially represented on a MNL as no SNARC effect was
observed for the distractors’ magnitudes while a robust distance effect was present.
Consequently, number magnitude can be processed without automatic activation of its spatial
code. This spatial code may only be activated in conditions in which spatial processing is
salient and does not require much attention.
In the current study, the mental numerical interval may be the most salient spatial
reference frame. If the right IPS region were mainly responsible for linking number
magnitude and spatial representation, damage to this right IPS region would be particularly
impairing for this most salient spatial reference frame. In contrast, magnitude processing
which is less spatially salient may be less impaired as the left IPS, which may be less involved
in spatial representation of magnitude, can take over. Although this hypothesis of differential
involvement of the two IPS in the spatial processing of magnitude offers an account for the
result pattern observed in the current study, it should be further investigated in the future.
Finally, the fact that we did not observe any group differences with regard to
multiplicativity may be due to two reasons: First, multiplication fact knowledge is presumably
located in the left gyrus angularis (cf. Dehaene et al., 2003; Delazer et al., 2003) which was
not lesioned in our neglect patients (see Table 1 for lesion sites of neglect patients). Second,
in contrast to previous studies, we did not even observe a main effect of multiplicativity. The
absence of an effect of multiplicativity may be explained by two related factors: first, the low
222