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

preclude any attentional bias towards the tens, making decade and unit digits equally relevant.
If two-digit numbers were represented internally in a holistic fashion, these changes should
not matter. However, if numbers were represented internally in a decomposed fashion, these
changes should be relevant and should produce significant unit-based effects, in particular the
compatibility effect. Note that this prediction is made although we could do nothing about the
third problem as the congruency effect is inevitably confounded with the examination of
internal representations.
METHOD
Participants: 19 students of the University of Salzburg (11 female) participated in the
experiment. Mean age was 21.8 years (SD: 2.4 years; range: 18 - 27 years). All participants
reported normal or corrected to normal vision and were right-handed.
Stimuli: In the current experiment two-digit numbers ranging from 31 to 79 had to be
compared to the two standard numbers 53 and 57. The stimulus set did not contain multipliers
of ten and - depending on the standard employed - either the number 53 or 57 was omitted.
Probe numbers smaller or larger than the standard were balanced in frequency of occurrence
as was the number of between- (e.g. 53_45) and within-decade trials (e.g. 53_58). This latter
requirement was met by selective repetitions of within-decade stimuli. Altogether, 72 probe
numbers had to be compared to either standard. 36 probe numbers were between-decade
stimuli, 18 smaller (31 - 49 excluding 40) and 18 larger than the standard (61 - 79 excluding
70). Additionally, 36 within-decade stimuli were presented, again 18 smaller and 18 larger
than the standard. To attain this balanced stimulus set, for the standard 57, each number from
51 - 56 was presented 3 times, and 58 and 59 both 9 times, and accordingly we included 9
times both 51 and 52 and 3 times 54 - 59 for the standard 53.
All probes were shown in Arabic notation using the “Times New Roman” font (size
24) and were presented at the centre of a 17‘ monitor.
48