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

may be determined by the presentational format employed in the respective studies. These
authors argue that evidence suggesting separate processing of decade and unit digit
magnitudes comes from studies in which both to-be-compared numbers were presented
externally (e.g., 37_53). Additionally, they presented empirical evidence indicating holistic
rather than decomposed processing of tens and units when only one number is presented and
had to be compared to an internally memorized standard (Zhang & Wang, 2005). In the first
study, when participants had to compare a given probe to an internal standard, empirical
evidence for decomposed processing of two-digit number magnitude was observed as
indicated by a standard unit-decade compatibility effect and its characteristic interaction with
unit distance (i.e., a more pronounced compatibility effect for large unit distances). These
results are hard to reconcile with the notion of a holistic internal representation of two-digit
number magnitude in which the place-value structure of the Arabic number system is not
retained.
In Study 2 the influence of place-value information on the solving of basic arithmetic
addition problems was investigated. It was hypothesized that place-value information is
especially important in addition problems in which the execution of a carry operation is
needed. In such trials the decade digit of the unit digit sum has to be carried to the result’s
decade digit to calculate the correct result, thereby, requiring processes of place-value, i.e.,
unit-decade integration. More particularly, it was expected that the basic processes of (i)
calculating the unit sum to determine whether a carry is needed or not, and (ii) the updating of
the decade digit of the result should be dissociable by evaluating participants’ eye fixation
behaviour. Based on the eye-mind and immediacy assumption (cf. Rayner & Pollatsek, 1989),
a more pronounced increase in the number of fixations on the unit digits of the summands
should be found if the difficulty of carry addition problems arises from computing the twodigit
sum of these unit digits. Otherwise, if updating the decade digit of the result causes the
difficulty of carry addition problems, there should be a steeper increase in the number of
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