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

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prominent role <strong>of</strong> <strong>the</strong> unit digits <strong>of</strong> <strong>the</strong> summands in mental addition (Klein et al., under<br />

revision). Ra<strong>the</strong>r, <strong>the</strong> data also served as a generalization <strong>of</strong> <strong>the</strong> findings by Moeller and coworkers<br />

(2009a) as <strong>the</strong>y provide fur<strong>the</strong>r eye tracking evidence validating <strong>the</strong> assumption <strong>of</strong><br />

parallel but decomposed processing <strong>of</strong> two-digit <strong>number</strong>s not only in a task as basic as<br />

<strong>number</strong> magnitude comparison but also in mental addition.<br />

So far, <strong>the</strong> evidence provided by <strong>the</strong> current <strong>the</strong>sis regarding <strong>the</strong> role <strong>of</strong> <strong>the</strong> <strong>place</strong>-<strong>value</strong><br />

<strong>structure</strong> <strong>of</strong> <strong>the</strong> <strong>Arabic</strong> <strong>number</strong> system within <strong>the</strong> human representation <strong>of</strong> multi-digit <strong>number</strong><br />

magnitude was empirical in nature. However, in Study 7 <strong>the</strong> question in which way two-digit<br />

<strong>number</strong> magnitude is represented (i.e., ei<strong>the</strong>r holistically <strong>the</strong>reby not retaining <strong>the</strong> <strong>place</strong>-<strong>value</strong><br />

structuring or decomposed or hybrid and thus referencing <strong>place</strong>-<strong>value</strong> principles) was pursued<br />

by a computational approach.<br />

Computational evidence on <strong>the</strong> nature <strong>of</strong> two-digit <strong>number</strong> magnitude representation<br />

On a more <strong>the</strong>oretical level <strong>the</strong> current <strong>the</strong>sis also added significantly to our<br />

understanding <strong>of</strong> how two-digit <strong>number</strong>s are represented. As already elaborated on above, <strong>the</strong><br />

empirical findings <strong>of</strong> <strong>the</strong> present <strong>the</strong>sis consistently provide evidence for <strong>the</strong> notion <strong>of</strong> twodigit<br />

<strong>number</strong> magnitude being represented and processed in a decomposed manner separating<br />

tens and units; and thus explicitly complying with <strong>the</strong> <strong>place</strong>-<strong>value</strong> <strong>structure</strong> <strong>of</strong> <strong>the</strong> <strong>Arabic</strong><br />

<strong>number</strong> system. However, currently <strong>the</strong>re are two <strong>the</strong>oretical frameworks capable <strong>of</strong><br />

accounting for such decomposed processing: <strong>The</strong> notion <strong>of</strong> a strictly decomposed<br />

representation <strong>of</strong> multi-digit <strong>number</strong>s separated into <strong>the</strong>ir constituting digits (cf. Verguts & De<br />

Moor, 2005) as well as <strong>the</strong> hybrid model <strong>of</strong> multi-digit <strong>number</strong> representation assuming an<br />

additional holistic representation <strong>of</strong> <strong>the</strong> overall magnitude <strong>of</strong> a <strong>number</strong> despite <strong>the</strong> separate<br />

representations <strong>of</strong> units, tens, hundreds, etc. (cf. Nuerk & Willmes, 2005; Nuerk et al., 2001).<br />

As <strong>the</strong>re is currently no empirical paradigm allowing for differentiating between <strong>the</strong>se two<br />

<strong>the</strong>oretical models, we addressed this question by a computational approach. Three<br />

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