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

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DISCUSSION<br />

<strong>The</strong> effects <strong>of</strong> neglect on <strong>the</strong> bisection <strong>of</strong> numerical intervals in <strong>the</strong> present study can be<br />

summarized as follows: First, <strong>the</strong> ANOVA revealed that neglect patients benefited reliably<br />

less when <strong>the</strong> central <strong>number</strong> was smaller than <strong>the</strong> arithmetical middle (e.g. 21_22_35)<br />

compared to when it was larger (e.g. 21_34_35). Second, it was observed that neglect patients<br />

were especially impaired for triplets crossing a decade boundary (e.g. 25_28_31) compared to<br />

triplets within <strong>the</strong> same decade (e.g. 22_25_28). Finally, neglect patients were not generally<br />

impaired in all numerical representations: Nei<strong>the</strong>r <strong>the</strong> effect <strong>of</strong> distance to <strong>the</strong> arithmetical<br />

middle nor that <strong>of</strong> multiplicativity differed between neglect patients and non-neglect controls.<br />

According to Nuerk et al. (2002; see also Moeller, 2006), participants’ response<br />

latencies are shorter for triplets with <strong>the</strong> central <strong>number</strong> being numerically smaller than <strong>the</strong><br />

arithmetical middle compared to triplets with a central <strong>number</strong> larger than arithmetical<br />

middle. This general beneficial effect was replicated in <strong>the</strong> present study. However, neglect<br />

patients benefited reliably less than non-neglect controls when <strong>the</strong> central <strong>number</strong> was smaller<br />

than <strong>the</strong> arithmetical middle. From this it can be inferred that neglect patients neglect <strong>the</strong> left<br />

side <strong>of</strong> a given numerical interval.<br />

It can be hypo<strong>the</strong>sized that <strong>the</strong> effect <strong>of</strong> neglect on <strong>the</strong> mental numerical interval is<br />

stronger for <strong>number</strong>s far<strong>the</strong>r towards <strong>the</strong> left side <strong>of</strong> that interval than for <strong>number</strong>s which are<br />

on <strong>the</strong> left side <strong>of</strong> <strong>the</strong> interval but relatively close to <strong>the</strong> middle. Although <strong>the</strong>re was no<br />

reliable three-way interaction between group, size relative to <strong>the</strong> middle, and distance to <strong>the</strong><br />

middle, fine-grained analyses revealed that this hypo<strong>the</strong>sis tended to be true. While for<br />

<strong>number</strong>s close to <strong>the</strong> arithmetical middle, neglect patients and controls differed only<br />

marginally; for <strong>number</strong>s far from <strong>the</strong> middle, <strong>the</strong>re was a significant group effect: For those<br />

far distances, neglect patients benefited significantly less when <strong>the</strong> central <strong>number</strong> was<br />

smaller than <strong>the</strong> arithmetical middle than when it was larger. <strong>The</strong>se findings extend previous<br />

results from Zorzi et al. (2002; and later Priftis et al., 2006; Rossetti et al., 2004 and Zorzi et<br />

219

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