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

Pollatsek, 1989) states that an object or stimulus is processed as long as it is fixated. Thereby,
the number of fixations as well as their durations is a valid predictor of how important
information from a specific part of a stimulus (e.g., a particular digit) is in the context of
performing the task at hand.
Based on above considerations, the eye-tracking methodology should also offer the
possibility to differentiate between different basic processes underlying place-value
integration. A question pursued in Study 2 of the current thesis. Here, participants’ eye
fixation behaviour in an addition verification task was evaluated to investigate possible
origins of difficulty in carry addition problems. We were able to identify two distinct
processes associated with the increased difficulty of carry addition problems each reflecting
processes of place-value integration. On the one hand, performing carry addition problems
seemed to be associated with specific unit based calculations indicating the requirement of a
carry when reaching or exceeding a certain level (i.e., a unit sum of ≥ 10). This suggested that
particular processing of the unit digits of the summand was necessary whenever the sum of
these digits becomes a two-digit number and thus the decade digit of the unit sum has to be
carried to the decade position to update the decade digit of the result. On the other hand, the
results indexed a process of carry execution to add to overall difficulty as well. In carry
addition problems the decade digit of the result required specific processing, possibly being
associated by the updating of the sum of the decade digits of the summands by the carry from
the sum of the unit digits. Thus, being able to dissociate these different processes and to
associate them with the processing of specific digits (i.e., units of the summands vs. tens of
the result) again argues for a decomposed representation of number magnitude. When
assuming the magnitude of a two-digit number to be represented as an integrated entity not
retaining any place-value information there should performance in two-digit addition should
not be determined by processes that can certainly be attributed to the processing of either tens
or units. Thereby, the results of Study 2 not only corroborated earlier findings suggesting a
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