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

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primarily necessary for solving <strong>the</strong> NBT. <strong>The</strong>refore, participants need to verify <strong>the</strong><br />

applicability <strong>of</strong> <strong>the</strong>se rules for each trial. For that, it is necessary to monitor in parallel <strong>the</strong><br />

different numerical properties <strong>of</strong> <strong>the</strong> triplet as well as to inhibit <strong>the</strong> magnitude processing. In<br />

<strong>the</strong> present study, participants were able to monitor for multiplicativity, presence <strong>of</strong> decadecrossing<br />

distance from <strong>the</strong> central <strong>number</strong> to <strong>the</strong> mean and <strong>number</strong> magnitude. Fur<strong>the</strong>rmore,<br />

part <strong>of</strong> <strong>the</strong> activation observed in <strong>the</strong> superior frontal gyrus may be due to inhibition processes<br />

(Konishi et al., 2003) suppressing magnitude manipulations as <strong>the</strong>se are not required in<br />

triplets for which <strong>the</strong> correct response can be inferred by using a procedural rule. For instance,<br />

in triplets without decade crossing participants may have inhibited <strong>the</strong> magnitude <strong>of</strong> tens<br />

because <strong>the</strong> comparison <strong>of</strong> unit distances is sufficient for responding correctly. Fur<strong>the</strong>rmore,<br />

in multiplicative triplets <strong>the</strong> central <strong>number</strong> is per definition <strong>the</strong> correct mean <strong>of</strong> <strong>the</strong> interval.<br />

<strong>The</strong>refore, no magnitude processing would be needed at all. Additionally, in triplets with a<br />

large distance to <strong>the</strong> mean, <strong>the</strong> central <strong>number</strong> is numerically too close to one <strong>of</strong> <strong>the</strong> outer<br />

<strong>number</strong>s to be <strong>the</strong> correct mean <strong>of</strong> <strong>the</strong> interval. Again, magnitude manipulations may be<br />

discontinued in <strong>the</strong>se cases 1 .<br />

In <strong>the</strong> particular case <strong>of</strong> <strong>the</strong> stronger activation in <strong>the</strong> angular gyrus found for<br />

multiplicatively related triplets, a second account for <strong>the</strong> current data is possible. Apart from<br />

<strong>the</strong> above-mentioned monitoring and inhibitory mechanisms, activation <strong>of</strong> <strong>the</strong> left angular<br />

gyrus has also been associated with arithmetic fact knowledge (Delazer et al. 2003; 2005).<br />

Such an interpretation is also compatible with <strong>the</strong> data pattern observed for multiplicativity.<br />

<strong>The</strong>refore, <strong>the</strong> increased activation in <strong>the</strong> (left) angular gyrus may also indicate table-related<br />

multiplication facts are accessed while performing <strong>the</strong> NBT (Cohen et al., 2000).<br />

In summary, when <strong>number</strong>s keep well-learned relations with each o<strong>the</strong>r and <strong>the</strong>se<br />

relations are more frequently activated and manipulated, activation in <strong>the</strong> left inferior parietal<br />

cortex, especially in <strong>the</strong> angular gyrus increased. Moreover, activation <strong>of</strong> <strong>the</strong> superior frontal<br />

gyrus increased when a triplet could be solved by applying procedural rules. When none <strong>of</strong><br />

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