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

adjustment of the degrees of freedom. To further investigate in what way a carry operation
influenced the number of regressions (i.e., leftward saccades to a previous interest area)
initiated from either tens or units of both the second summand as well as the result a 2 x 2
ANOVA was conducted discerning the factors digit identity (decade vs. unit digit) and carry
(required vs. not required). Finally, despite the origin of the regressions also the target of the
regressions was appraised. For regressions from the second summand to the first summand a 2
x 2 ANOVA with the factors digit identity (decade vs. unit digit) and carry (required vs. not
required) was conducted while regressions originating from the result were analyzed by a 2 x
2 x 2 ANOVA involving the factors problem element (first vs. second summand), digit
identity (decade vs. unit digit), and carry (required vs. not required).
RESULTS
Participants who performed at or below chance level in at least one of the
experimental conditions where excluded from further analyses. This affected one participant.
For the other participants error rates ranged from 1.0 % to 13.3 % with the mean at 7.0 % and
a standard deviation of 3.4 %. Only response latencies followed by a correct classification
were considered for the RT analysis. Additionally, a trimming procedure eliminated all
latencies shorter than 200 ms and longer than 5000 ms in a first step. Subsequently, all RTs
falling below or above three standard deviations of an individual participant’s mean were
excluded from the analyses in a second step. For the analyses of the eye fixation data only
data from trials already included in the RT analysis were considered.
Classification performance
ANOVA: The ANOVA showed that both response latencies as well as error rates were
reliably influenced by problem size [RT: F(1, 18) = 86.26, p < .001; errors: F(1, 18) = 16.09,
p < .001, see Figure 1, Panel A]: addition problems with a relatively larger problem size
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