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

al. 2006). Neglect not only impairs access to relatively smaller numbers in the one-digit or
small two-digit range, it does so for the full range of two-digit numbers.
The second hypothesis outlined in the introduction was that neglect patients may have
particular difficulties with two-digit number triplets which cross a decade boundary compared
to triplets from within one decade. Indeed, we did not only observe a general decade crossing
main effect, but a reliable interaction with participant group: Neglect patients exhibited a
larger decade crossing effect than their non-neglect counterparts; i.e. they had particular
difficulties when the numbers of a triplet were from different decades.
The effect of decade crossing on behavioural performance (Nuerk et al. 2002) and fMRI
signal (Wood et al., 2008) has been interpreted as resulting from a deeper processing of
number magnitude and the base-10 structure of the Arabic number system required when
different decade digits are encountered in the task. Processing different decades seems to
demand the integration of decomposed decade digit and unit digit magnitudes (cf. Nuerk &
Willmes, 2005 for a discussion). Neglect patients may have problems mentally representing
the magnitude of two-digit numbers in a decomposed fashion, as they may have problems
representing the decade digit’s magnitude. This may lead to the more pronounced decade
crossing effect observed for neglect patients in the current study.
A perceptual account for this larger decade crossing effect is that neglect patients may
have difficulties perceiving the decade digit which is located on the left within a two-digit
number. This perceptual account is however not consistent with the diagnostic data of our
patients: All neglect patients were able to read aloud the two-digit numbers of a triplet
presented above each other without errors. Moreover, in the NET, the neglect patients were
even able to read four-digit digital clock times without major problems (one single error in
two of six patients). Moreover, this perceptual account is also disproved by more fine-grained
analyses: (Decade digit driven) problem size was a highly significant predictor of neglect
patients’ performance. So, neglect patients did not only perceive the visual presence of the
220