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

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2. Study 6: Impairments <strong>of</strong> <strong>the</strong> mental <strong>number</strong> line for two-digit <strong>number</strong>s in neglect.<br />

In <strong>the</strong>ir seminal paper Zorzi et al. (2002; see also Zorzi, Priftis, Meneghello,<br />

Marenzi, & Umiltà., 2006) observed that hemi-spatial neglect not only distorts <strong>the</strong><br />

representation <strong>of</strong> intra- and extra-personal space but that this impairment generalizes<br />

to <strong>the</strong> spatial representation <strong>of</strong> <strong>number</strong> magnitude, <strong>the</strong>reby disrupting <strong>the</strong> mental<br />

<strong>number</strong> line. Interestingly, <strong>the</strong> spatial mental representation <strong>of</strong> <strong>number</strong> magnitude was<br />

affected by hemi-spatial neglect in <strong>the</strong> same way as mental representation <strong>of</strong> physical<br />

space. In a NBT with <strong>number</strong>s up to 29 Zorzi and co-workers (2002) observed that<br />

patients’ bisection errors mirrored <strong>the</strong> error pattern in physical line bisection: first,<br />

neglect patients mis<strong>place</strong>d <strong>the</strong> numerical mean <strong>of</strong> a given interval to <strong>the</strong> right (e.g.,<br />

indicating 7 to be <strong>the</strong> midpoint between 1 and 9), second, <strong>the</strong> deviation between <strong>the</strong><br />

correct and <strong>the</strong> indicated midpoint <strong>of</strong> a given interval increased as <strong>the</strong> range <strong>of</strong> <strong>the</strong><br />

interval increased, and third, a cross-over effect was observed for very small interval<br />

ranges. As <strong>the</strong> NBT requires orienting and navigating along <strong>the</strong> mental <strong>number</strong> line we<br />

were interested whe<strong>the</strong>r such neglect effects could also be observed for <strong>the</strong> whole<br />

range <strong>of</strong> two-digit <strong>number</strong>s. More particularly, we were interested whe<strong>the</strong>r hemispatial<br />

neglect had <strong>influence</strong>s on <strong>the</strong> processing <strong>of</strong> <strong>place</strong>-<strong>value</strong> information as well.<br />

According to Nuerk and colleagues (2001, see also Nuerk and Willmes, 2005) <strong>the</strong>re<br />

may not exist just one analoge mental <strong>number</strong> line but separate <strong>number</strong> lines for <strong>the</strong><br />

different power levels <strong>of</strong> <strong>the</strong> <strong>Arabic</strong> <strong>number</strong> system (i.e., tens, units, etc.).<br />

Consequently, evaluation <strong>of</strong> <strong>the</strong> performance <strong>of</strong> neglect patients in a two-digit <strong>number</strong><br />

bisection task may be informative for clarifying whe<strong>the</strong>r processing <strong>of</strong> structural<br />

aspects <strong>of</strong> <strong>the</strong> <strong>Arabic</strong> <strong>number</strong> system is also impaired in neglect patients. <strong>The</strong>refore,<br />

<strong>the</strong> impact <strong>of</strong> neglect on <strong>the</strong> processing <strong>of</strong> decade crossings within <strong>the</strong> to-be-judged on<br />

triplets is <strong>of</strong> particular interest as in <strong>the</strong>se triplets processing <strong>of</strong> <strong>place</strong>-<strong>value</strong><br />

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