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

Children with an IQ (measured by CFT1; Catell, Weiss & Osterland, 1997) more than
1 SD below the average were excluded from the initial sample. This affected 2 children in
Austria and 10 children in Italy.
Stimuli and design: The number-line task used was a paper-pencil version of a
number-to-position task, requiring children to estimate the position of a given number on an
empty number-line. Each stimulus of the task involved a 10-cm line with the left end labeled
“0”, and the right end labeled “100”. The numbers to be estimated were printed centrally
above the line in Arabic notation. Participants had to mark the position of the following
numbers on the hypothetical number line in the given order: 27, 2, 64, 35, 7, 13, 99, 75, 47, 3,
11, 82, 95, 9, 17, 6, 18, and 53. Most important for the current study was the fact that no
verbal number word was (explicitly) involved in the task neither at the presentation nor at the
response level.
Procedure: Participants were tested in a one-to-one single session with the
experimenter. Trials were presented sequentially one by one. Children were told to neither
count nor use any other strategy but estimating the position of the presented number on the
line. The number-line task started with an initial orienting problem, followed by the
experimental problems. On the orienting problem, children were asked to estimate the
position of the number 50 for practice purposes. Neither further information before the
practice trial (e.g., indicating 50 to be the middle of the scale) nor feedback on performance
after the practice trials or any of the critical trials was given.
Analysis: In a first step, the deviation of estimated position from true position for
every single item was measured automatically to the nearest millimetre and the individual
deviation error of the estimated from the actual value (in percent) was computed for each
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