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

Thereby, possible interactions and interferences between the processing of the separate
representations were not implemented into the current versions of the decomposed as well as
the hybrid model. In turn, this rather minimalistic model architecture did not cover the entire
complexity of the hybrid model, in particular, for which specific inhibitory and excitatory
interrelations of the single representations are assumed (cf. Nuerk & Willmes, 2005). In this
sense, the decomposed comparisons of tens and units as assumed in the current models do
also not take into account possible comparison processes between the tens digit of the one
number and the unit digit of the other or even between the two digits constituting one number
which have been observed to occur when comparing two two-digit numbers (Wood, Nuerk, &
Mahr, 2005). Taken together, it has to be noted that the results of the present study have been
achieved using rather prototypical and simplified architectures for the three models of twodigit
number representations to-be-compared. Nevertheless, these results suggested that
computational modelling may be a fruitful methodological approach to evaluate the validity
of theoretical models on the structure of two-digit number magnitude representation.
Therefore, it is up to future studies to investigate whether the current findings also hold when
more specific aspects of the individual models are implemented into the architecture of the
computational models.
Another important point does not directly concern model architecture but more general
aspects of cognitive processing. Nuerk and co-workers have argued repeatedly that attentional
processes may play a role in two-digit number comparison (e.g., Nuerk & Willmes, 2005;
Moeller et al., 2009b). In particular, the size of the compatibility effect was found to be
influenced by the number of within-decade trials (e.g., 43_48) in the stimulus set. As in
within-decade trials the unit digit is decisive increasing number of within-decade trials means
that attentional focusing on the decade digits of the two to-be-compared numbers becomes
less and less beneficial. This results in a more balanced relevance of tens and units for the
decision and leads to a more pronounced compatibility effect. Additionally, in their current
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