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

previous studies on two-digit number comparison Nuerk et al. (2001) did not use a fixed
standard (e.g., 55 or 66, cf. Dehaene et al., 1990) to which a presented number had to be
compared. Instead, participants had to single out the larger number of a pair of two-digit
numbers. Generally, when comparing two two-digit numbers separate comparisons of tens
and units may result in either compatible or incompatible decision biases. For instance, in the
number pair 38_53 the larger number contains the smaller unit digit. Thereby, although the
overall relation also holds for the comparison of the tens digits it this is not the case for
comparing the unit digits (i.e., 28 < 53 and 2 < 5, but 8 > 3). Thus, separate comparisons of
tens and unit result in antidromic, i.e., incompatible decision biases. On the other hand, in a
number pair such as 42_57 the decision biases for the separate comparisons of tens and units
are both congruent with the overall decision (i.e., 42 > 57, 4 < 5, and 2 < 7). Nuerk and coworkers
observed that although overall distance was held constant between compatible and
incompatible number pairs (e.g., 15 in both examples above) incompatible number pairs were
followed by longer response latencies and more errors than their compatible counterparts. As
overall distance was matched between compatible and incompatible number pairs, no
compatibility effect should be obtained if an exclusively analogue (holistic) magnitude
representation were engaged. Replications of the compatibility effect for Arabic stimuli
arranged in different layouts (Nuerk, Weger, Willmes, 2004a; Ratinckx, Nuerk, van Dijk &
Willmes, 2006) and also for number words (Nuerk, Weger & Willmes, 2002a; 2005; Macizo,
& Herrera, in press) indicated that it is not a purely perceptual effect. Additionally,
interactions of the compatibility effect with distance measures of tens and units implicated
that it is not a common attentional congruity effect (i.e., large unit distances were associated
with a more pronounced compatibility effect for RTs, whereas the same relation was
observed for small decade distances and the compatibility effect for error rates). In other
words, the results cannot be explained by exclusively assuming a response conflict because
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