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

Such congruency is important as most compatible trials are incongruent whereas most
incompatible trials are congruent (see Wood et al., 2005; Nuerk & Willmes, 2005). Therefore,
when using a fixed internal standard the congruency effect works against the unit-based
compatibility effect and helps to produce unit-based null effects.
Objectives
We have briefly outlined how unit-based null effects can most likely be produced.
However, there is the problem that such null effects observed under the conditions stated
above are not conclusive. If one does not find unit-based effects under unfavourable
conditions, this does not mean that unit-based effects do not exist at all. Consequently, the
absence of unit-based effects under unfavourable conditions does not imply holistic
processing, especially not when unit-based effects can be obtained under more favourable
conditions.
The current study aimed to evaluate the conclusion of a holistic internal representation
of two-digit numbers as drawn by Zhang and Wang (2005) under more favourable conditions.
In their study the authors did not control for the above three unfavourable conditions: (i) Only
small unit distances were used as the standards were 55 and 65. (ii) The unit digits were
largely irrelevant in their study as only 13 % of the trials required within-decade comparisons.
(iii) In the internal representation condition, only one two-digit number was presented so that
the congruency effect worked against unit-based effects.
Based on these considerations the objective of the study is straightforward: Do the
results of Zhang and Wang (2005) indicating a holistic internal representation of two-digit
numbers hold even under conditions more favourable to detect unit-based effects indicative of
decomposed internal representations of tens and units? To directly test this, the experimental
design of Zhang and Wang was changed in two essential aspects: (i) The standards 53 and 57
were chosen to allow for larger unit distances. (ii) 50% within-decade trials were used to
47