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

Total reading time on target 2 : The ANOVA discerning the factors carry (required vs.
not required), problem element (first summand vs. second summand vs. result), and digit
identity (decade vs. unit digit) revealed reliable main effects of carry [F(1, 18) = 42.29, p <
.001] and problem element [F(2, 36) = 35.47, p < .001, see Figure 2, Panel A]. This indicated
that addition problems requiring a carry operation were associated with a higher average total
reading time per digit as compared to non-carry problems (354 ms vs. 267 ms, respectively).
Additionally, fixations were not distributed equally between the two summands and the result.
Post-hoc evaluations by the Games-Howell test indicated that total reading times were longest
on the second summand followed by the first summand and the result (450 ms vs. 293 ms vs.
187 ms, respectively). The main effect of digit identity was not significant [F(1, 18) = 1.40, p
= .25]. Moreover, the interaction of carry and problem element was reliable [F(2, 36) = 23.33,
p < .001, see Figure 2, Panel A]. Post-hoc comparisons by the Games-Howell test showed that
the increase in total reading time due to a required carry operation was most pronounced on
the second summand but did not differ between the first summand and the result (+ 156 ms
vs. + 64 ms vs. + 44 ms, respectively). Furthermore, problem element and digit identity
interacted significantly [F(2, 36) = 26.36, GG = 0.81, p < .001]. Post-hoc testing by the
Games Howell test indicated that the effect of digit identity (TRT on the unit digits – TRT on
the decade digits) was largest on the first summand but did not differ between the second
summand and the result (+ 399 ms vs. – 114 ms vs. – 170 ms, respectively). Additional t-tests
revealed that upon the first summand the unit digits were fixated reliably longer than the
decade digits (492 ms vs. 93 ms, respectively; t(18) = 7.22, p < .001), whereas this pattern
was reversed for the result. Here, longer TRT were observed on the decade digit than on the
unit digit (272 ms vs. 102 ms fixations, respectively; t(18) = 4.35, p < .001). However, for the
second summand no significant difference between the total reading times on either the unit
2 Please note that the analyses of the eye fixation behaviour were based on addition problems with a large
problem size only. As addition problems with a small problem size also involved single-digit numbers the
distribution of fixations across decade and unit digits would have been biased for these trials.
73