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

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activation <strong>of</strong> <strong>the</strong> output layer is a combination <strong>of</strong> <strong>the</strong> activation <strong>of</strong> <strong>the</strong> hidden layer for <strong>the</strong><br />

comparisons <strong>of</strong> tens, units, and overall magnitude this indicated a very small and unspecific<br />

<strong>influence</strong> <strong>of</strong> <strong>the</strong> unit digits on <strong>the</strong> output in <strong>the</strong> hybrid model. For <strong>the</strong> compatibility effect this<br />

implies that its successful simulation by <strong>the</strong> hybrid model for <strong>the</strong> case <strong>of</strong> comparisons to a<br />

variable standard may not be primarily driven by specific activation differences <strong>of</strong> <strong>the</strong> unit<br />

digits between compatible and incompatible <strong>number</strong> pairs. Ra<strong>the</strong>r, <strong>the</strong> compatibility effect<br />

may be due to systematic differences in <strong>the</strong> difference between <strong>the</strong> activations for overall<br />

magnitude and that for <strong>the</strong> tens digit. As <strong>the</strong> separate representations <strong>of</strong> tens, units, and overall<br />

magnitude were assumed to be linear in <strong>the</strong> current computational models <strong>the</strong> latter difference<br />

never<strong>the</strong>less provides an indirect measure <strong>of</strong> <strong>the</strong> unit distance. <strong>The</strong>reby, <strong>the</strong> compatibility<br />

effect observed for <strong>the</strong> data produced by <strong>the</strong> hybrid model is not based on <strong>the</strong> direct<br />

comparisons <strong>of</strong> <strong>the</strong> unit digits <strong>of</strong> <strong>the</strong> two to-be-compared <strong>number</strong>s but by a derivate <strong>of</strong> <strong>the</strong><br />

comparisons <strong>of</strong> overall magnitude and <strong>the</strong> tens. However, this indirect <strong>influence</strong> <strong>of</strong> <strong>the</strong> unit<br />

digits on overall performance differs from <strong>the</strong> <strong>influence</strong> originally assumed by Nuerk and<br />

Willmes (2005) for <strong>the</strong> hybrid model.<br />

In summary, evaluation <strong>of</strong> <strong>the</strong> connection weights indicated <strong>the</strong> compatibility effect to<br />

originate from different sources in <strong>the</strong> strictly decomposed and <strong>the</strong> hybrid model.<br />

Interestingly, only <strong>the</strong> compatibility effect observed for <strong>the</strong> data by <strong>the</strong> decomposed model<br />

seemed to arise from <strong>the</strong> separate comparisons <strong>of</strong> tens and units <strong>of</strong> <strong>the</strong> to-be-compared twodigit<br />

<strong>number</strong>s. On <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> compatibility effect found for <strong>the</strong> hybrid model data<br />

seemed to be <strong>the</strong> result <strong>of</strong> differences between <strong>the</strong> representations <strong>of</strong> overall magnitude and<br />

<strong>the</strong> tens digits. Thus, only <strong>the</strong> comparison process realized by <strong>the</strong> decomposed model is in line<br />

with <strong>the</strong> original assumptions <strong>of</strong> <strong>the</strong> hybrid model as promoted by Nuerk and Willmes (2005;<br />

see also Knops, 2006). A probable reason for <strong>the</strong> obtained pattern <strong>of</strong> result may be linear<br />

dependency between overall magnitude, tens magnitude, and unit magnitude when assuming<br />

linear coding <strong>of</strong> all <strong>of</strong> <strong>the</strong>se symbolic representations.<br />

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