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

In line with this prediction, total reading times on the decade digit of the result were
specifically increased in carry as compared to non-carry addition problems. This finding
indeed corroborated the interpretation that the execution of the carry procedure may represent
the application of a procedural rule (i.e., “when the sum of the unit digits is equal or larger
than 10 add the decade digit of the unit sum to the sum of the decade digits of the
summands”). As for the unit-based calculations upon the unit digits of the summands,
inspection of the regressions was also informative on processes related to executing the carry.
In line with the argument that the execution of the carry may be specifically associated with
processing the decade digit of the result (seeming to reflect processes of updating the decade
sum of the summands by the carry) it was observed that most regressions from the result back
to the summands started from the decade digit. Moreover, it was found that most of these
regressions were directed to the decade digits of the summands and to the decade digit of the
second summand, in particular. On the one hand, this corroborates the interpretation that
processes concerning the execution of a carry in an addition verification paradigm involved
specific processing of the decade digit of the result and its constituents, i.e., the decade digits
of the summands. On the other hand, the results of analyzing the regressions also indicate that
the increase of total reading time as observed upon the decade digit of the second summand
may be driven by reinspections of this particular digit to come to the correct decade digit of
the result in carry addition problems (see Figure 2 B) rather than being associated with
initially evaluating whether a carry is needed or not.
Taken together, the present results are meaningful in three respects: First, in line with
the results of Moeller et al. (2009a) the unbalanced distribution of fixations between tens and
units corroborated the notion of tens and units being processed separately rather than
integrated as the holistic representation of the whole number they constitute. Second, the
results of analyzing the regressions indicated that, in the current paradigm, processes
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