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

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Tippet (1996) have shown that patients with brain lesions extending to <strong>the</strong> right ventral<br />

prefrontal cortex were selectively impaired in tasks involving <strong>the</strong> generation <strong>of</strong> alternative<br />

solutions for a problem. Fur<strong>the</strong>rmore, Goel and Vartarian (2005) reported increased activation<br />

in this region when participants successfully generated alternative solutions for a task.<br />

In <strong>the</strong> present study, <strong>the</strong> right ventrolateral prefrontal cortex was <strong>the</strong> only region (see<br />

Figure 2B) showing more activation for non-bisectable triplets. <strong>The</strong>se results suggest that <strong>the</strong><br />

right ventrolateral prefrontal cortex is relevant for checking, whe<strong>the</strong>r <strong>the</strong> comparison between<br />

<strong>the</strong> mean <strong>of</strong> <strong>the</strong> interval and <strong>the</strong> central <strong>number</strong> should be completed or not. When <strong>the</strong> mean<br />

<strong>of</strong> <strong>the</strong> two outer <strong>number</strong>s is not an integer <strong>number</strong> (e.g. for 21_25_30 <strong>the</strong> mean <strong>of</strong> 21 and 30<br />

is 25.5), <strong>number</strong> magnitude comparison should be discontinued, because <strong>the</strong> central <strong>number</strong><br />

cannot be <strong>the</strong> correct response <strong>of</strong> <strong>the</strong> bisection. Behavioural data are in line with<br />

neur<strong>of</strong>unctional evidence showing that activation in <strong>the</strong> ventrolateral prefrontal cortex is<br />

specific for cognitive set changes (Goel & Vartarian, 2005). While responses to nonbisectable<br />

triplets presented in isolation were significantly faster than to bisectable triplets,<br />

response latencies for non-bisectable triplets following ano<strong>the</strong>r non-bisectable triplet did not<br />

differ from that for bisectable triplets. This increase in reaction time may reflect costs<br />

imposed by again activating <strong>the</strong> original cognitive set which specified a comparison between<br />

<strong>the</strong> mean <strong>of</strong> <strong>the</strong> interval and <strong>the</strong> central <strong>number</strong>.<br />

Since right ventrolateral prefrontal cortex is engaged in <strong>the</strong> rational use <strong>of</strong> cognitive<br />

resources and cognitive set changes, we suggest that this area may be considered part <strong>of</strong> <strong>the</strong><br />

neural system subserving procedural and conceptual knowledge about <strong>number</strong>s and <strong>the</strong>ir<br />

manipulations.<br />

CONCLUSIONS<br />

<strong>The</strong> results <strong>of</strong> <strong>the</strong> present study strongly suggest that different neurocognitive systems<br />

dedicated to (i) magnitude and symbolic base-10 processing, (ii) familiarity, monitoring and<br />

201

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