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

digit numbers were engaged. Additionally, the observed interaction of compatibility with unit
distance (i.e., a more pronounced compatibility effect for large as compared to small unit
distances) indicates that no common attentional congruity effect can be taken to be
responsible for that finding. Thus, a model accounting for the compatibility effect must allow
to differentiate between processing the tens numeral and the unit numeral – hence a model of
decomposed two-digit number processing.
Nuerk and co-workers repeatedly observed (logarithmic) overall distance to be a
reliable predictor of item RT in multiple stepwise regression analyses (cf. Nuerk et al., 2001;
2002; Moeller et al., 2009a; Wood et al., 2006). The authors interpreted the impact of overall
distance between the to-be-compared numbers to be due to a holistic representation of the
overall magnitude of the numbers involved, which cannot be accounted for by strictly
decomposed representations of tens and units (see Nuerk & Willmes, 2005, for a detailed
discussion of this argument). Based on these considerations, Nuerk and Willmes (2005)
proposed the hybrid model of two-digit number processing (see also Nuerk et al., 2001). The
decomposition part of the model accounts for the compatibility effect (which is hard to
reconcile with a purely holistic magnitude representation), while the holistic part of the model
would account for the influence of (logarithmic) overall distance.
Taken together, there is considerable empirical evidence for the existence of
decomposed processing in multi-digit numbers (e.g., Nuerk et al., 2001; Moeller et al., 2009a;
see also Domahs, Delazer, & Nuerk, 2006; Hoeckner et al., 2008; Nuerk et al., 2002;
Ratinckx, Nuerk, van Dijk, & Willmes, 2006; Verguts & de Moor, 2005; for further evidence
on decomposed processing other than the compatibility effect). So far there is no empirical
way to distinguish between the strictly decomposed and the hybrid model based on their
implications for number comparison. Another weakness is the qualitative nature of the
models of two-digit number processing. Neither the holistic nor the decomposed or the hybrid
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