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

participants for between-decade trials an ANCOVA was conducted over all included items
incorporating above mentioned factors. Additionally, a stepwise regression analysis was run
over all included items including the following predictors: (i) overall absolute distance, (ii)
logarithm of the absolute distance, (iii) distance of the logarithmic magnitudes, (iv) decade
distance, (v) logarithmic decade distance, (vi) problem size, (vii) logarithmic problem size,
(viii) unit distance ranging from -6 for e.g. 71_57 to +6 for e.g. 53_69, (ix) absolute unit
distance and (x) compatibility.
As within-decade trials were only included to preclude participants from focussing
their attention exclusively on the decade digit, these were treated as filler items and no further
analysis was carried out.
RESULTS
Overall mean error rate was very low (standard 53: 3.0 %, standard 57: 3.5 %) and
will not be considered here in greater detail. However, in line with earlier findings (e.g. Nuerk
et al., 2001) a reliable compatibility effect was present for error rates, too [F(1, 18) = 7.06, p <
.05, compatible: 1.7 % vs. incompatible: 3.0 % errors].
ANCOVA: Although the incorporated covariate, i.e. problem size, accounted for a
significant part of the variance [F(1, 39) = 5.13, p < .05], a reliable compatibility effect [F(1,
39) = 8.22, p < .01] was observed in the ANCOVA: compatible trials (492 ms) were followed
by shorter response latencies than incompatible trials (504 ms) 2 . Neither the main effect of
standard number [F(1, 39) < 1] or unit distance [F(1, 39) < 1] nor any interaction [all F <
1.47, all p > .24] was significant. However, when differentially evaluating the compatibility
effect for small and large unit distances, separate ANCOVAs with problem size as a covariate
showed that the overall main effect of compatibility was mainly driven by a reliable
2 Note that the compatibility effect was also reliable when running the analysis over participants instead [12 ms,
F(1, 18) = 8.04, p < .01] indicating that it was not moderated by problem size differences.
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